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llvm-6502/lib/Transforms/IPO/SimplifyLibCalls.cpp
Jeff Cohen 66c5fd6c53 When a function takes a variable number of pointer arguments, with a zero 
pointer marking the end of the list, the zero *must* be cast to the pointer
type.  An un-cast zero is a 32-bit int, and at least on x86_64, gcc will
not extend the zero to 64 bits, thus allowing the upper 32 bits to be
random junk.

The new END_WITH_NULL macro may be used to annotate a such a function
so that GCC (version 4 or newer) will detect the use of un-casted zero
at compile time.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@23888 91177308-0d34-0410-b5e6-96231b3b80d8
2005-10-23 04:37:20 +00:00

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//===- SimplifyLibCalls.cpp - Optimize specific well-known library calls --===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by Reid Spencer and is distributed under the
// University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements a module pass that applies a variety of small
// optimizations for calls to specific well-known function calls (e.g. runtime
// library functions). For example, a call to the function "exit(3)" that
// occurs within the main() function can be transformed into a simple "return 3"
// instruction. Any optimization that takes this form (replace call to library
// function with simpler code that provides the same result) belongs in this
// file.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "simplify-libcalls"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Instructions.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/ADT/hash_map"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/Debug.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Transforms/IPO.h"
#include <iostream>
using namespace llvm;
namespace {
/// This statistic keeps track of the total number of library calls that have
/// been simplified regardless of which call it is.
Statistic<> SimplifiedLibCalls("simplify-libcalls",
"Number of library calls simplified");
// Forward declarations
class LibCallOptimization;
class SimplifyLibCalls;
/// This hash map is populated by the constructor for LibCallOptimization class.
/// Therefore all subclasses are registered here at static initialization time
/// and this list is what the SimplifyLibCalls pass uses to apply the individual
/// optimizations to the call sites.
/// @brief The list of optimizations deriving from LibCallOptimization
static hash_map<std::string,LibCallOptimization*> optlist;
/// This class is the abstract base class for the set of optimizations that
/// corresponds to one library call. The SimplifyLibCalls pass will call the
/// ValidateCalledFunction method to ask the optimization if a given Function
/// is the kind that the optimization can handle. If the subclass returns true,
/// then SImplifyLibCalls will also call the OptimizeCall method to perform,
/// or attempt to perform, the optimization(s) for the library call. Otherwise,
/// OptimizeCall won't be called. Subclasses are responsible for providing the
/// name of the library call (strlen, strcpy, etc.) to the LibCallOptimization
/// constructor. This is used to efficiently select which call instructions to
/// optimize. The criteria for a "lib call" is "anything with well known
/// semantics", typically a library function that is defined by an international
/// standard. Because the semantics are well known, the optimizations can
/// generally short-circuit actually calling the function if there's a simpler
/// way (e.g. strlen(X) can be reduced to a constant if X is a constant global).
/// @brief Base class for library call optimizations
class LibCallOptimization
{
public:
/// The \p fname argument must be the name of the library function being
/// optimized by the subclass.
/// @brief Constructor that registers the optimization.
LibCallOptimization(const char* fname, const char* description )
: func_name(fname)
#ifndef NDEBUG
, occurrences("simplify-libcalls",description)
#endif
{
// Register this call optimizer in the optlist (a hash_map)
optlist[fname] = this;
}
/// @brief Deregister from the optlist
virtual ~LibCallOptimization() { optlist.erase(func_name); }
/// The implementation of this function in subclasses should determine if
/// \p F is suitable for the optimization. This method is called by
/// SimplifyLibCalls::runOnModule to short circuit visiting all the call
/// sites of such a function if that function is not suitable in the first
/// place. If the called function is suitabe, this method should return true;
/// false, otherwise. This function should also perform any lazy
/// initialization that the LibCallOptimization needs to do, if its to return
/// true. This avoids doing initialization until the optimizer is actually
/// going to be called upon to do some optimization.
/// @brief Determine if the function is suitable for optimization
virtual bool ValidateCalledFunction(
const Function* F, ///< The function that is the target of call sites
SimplifyLibCalls& SLC ///< The pass object invoking us
) = 0;
/// The implementations of this function in subclasses is the heart of the
/// SimplifyLibCalls algorithm. Sublcasses of this class implement
/// OptimizeCall to determine if (a) the conditions are right for optimizing
/// the call and (b) to perform the optimization. If an action is taken
/// against ci, the subclass is responsible for returning true and ensuring
/// that ci is erased from its parent.
/// @brief Optimize a call, if possible.
virtual bool OptimizeCall(
CallInst* ci, ///< The call instruction that should be optimized.
SimplifyLibCalls& SLC ///< The pass object invoking us
) = 0;
/// @brief Get the name of the library call being optimized
const char * getFunctionName() const { return func_name; }
#ifndef NDEBUG
/// @brief Called by SimplifyLibCalls to update the occurrences statistic.
void succeeded() { DEBUG(++occurrences); }
#endif
private:
const char* func_name; ///< Name of the library call we optimize
#ifndef NDEBUG
Statistic<> occurrences; ///< debug statistic (-debug-only=simplify-libcalls)
#endif
};
/// This class is an LLVM Pass that applies each of the LibCallOptimization
/// instances to all the call sites in a module, relatively efficiently. The
/// purpose of this pass is to provide optimizations for calls to well-known
/// functions with well-known semantics, such as those in the c library. The
/// class provides the basic infrastructure for handling runOnModule. Whenever
/// this pass finds a function call, it asks the appropriate optimizer to
/// validate the call (ValidateLibraryCall). If it is validated, then
/// the OptimizeCall method is also called.
/// @brief A ModulePass for optimizing well-known function calls.
class SimplifyLibCalls : public ModulePass
{
public:
/// We need some target data for accurate signature details that are
/// target dependent. So we require target data in our AnalysisUsage.
/// @brief Require TargetData from AnalysisUsage.
virtual void getAnalysisUsage(AnalysisUsage& Info) const
{
// Ask that the TargetData analysis be performed before us so we can use
// the target data.
Info.addRequired<TargetData>();
}
/// For this pass, process all of the function calls in the module, calling
/// ValidateLibraryCall and OptimizeCall as appropriate.
/// @brief Run all the lib call optimizations on a Module.
virtual bool runOnModule(Module &M)
{
reset(M);
bool result = false;
// The call optimizations can be recursive. That is, the optimization might
// generate a call to another function which can also be optimized. This way
// we make the LibCallOptimization instances very specific to the case they
// handle. It also means we need to keep running over the function calls in
// the module until we don't get any more optimizations possible.
bool found_optimization = false;
do
{
found_optimization = false;
for (Module::iterator FI = M.begin(), FE = M.end(); FI != FE; ++FI)
{
// All the "well-known" functions are external and have external linkage
// because they live in a runtime library somewhere and were (probably)
// not compiled by LLVM. So, we only act on external functions that
// have external linkage and non-empty uses.
if (!FI->isExternal() || !FI->hasExternalLinkage() || FI->use_empty())
continue;
// Get the optimization class that pertains to this function
LibCallOptimization* CO = optlist[FI->getName().c_str()];
if (!CO)
continue;
// Make sure the called function is suitable for the optimization
if (!CO->ValidateCalledFunction(FI,*this))
continue;
// Loop over each of the uses of the function
for (Value::use_iterator UI = FI->use_begin(), UE = FI->use_end();
UI != UE ; )
{
// If the use of the function is a call instruction
if (CallInst* CI = dyn_cast<CallInst>(*UI++))
{
// Do the optimization on the LibCallOptimization.
if (CO->OptimizeCall(CI,*this))
{
++SimplifiedLibCalls;
found_optimization = result = true;
#ifndef NDEBUG
CO->succeeded();
#endif
}
}
}
}
} while (found_optimization);
return result;
}
/// @brief Return the *current* module we're working on.
Module* getModule() const { return M; }
/// @brief Return the *current* target data for the module we're working on.
TargetData* getTargetData() const { return TD; }
/// @brief Return the size_t type -- syntactic shortcut
const Type* getIntPtrType() const { return TD->getIntPtrType(); }
/// @brief Return a Function* for the fputc libcall
Function* get_fputc(const Type* FILEptr_type)
{
if (!fputc_func)
{
std::vector<const Type*> args;
args.push_back(Type::IntTy);
args.push_back(FILEptr_type);
FunctionType* fputc_type =
FunctionType::get(Type::IntTy, args, false);
fputc_func = M->getOrInsertFunction("fputc",fputc_type);
}
return fputc_func;
}
/// @brief Return a Function* for the fwrite libcall
Function* get_fwrite(const Type* FILEptr_type)
{
if (!fwrite_func)
{
std::vector<const Type*> args;
args.push_back(PointerType::get(Type::SByteTy));
args.push_back(TD->getIntPtrType());
args.push_back(TD->getIntPtrType());
args.push_back(FILEptr_type);
FunctionType* fwrite_type =
FunctionType::get(TD->getIntPtrType(), args, false);
fwrite_func = M->getOrInsertFunction("fwrite",fwrite_type);
}
return fwrite_func;
}
/// @brief Return a Function* for the sqrt libcall
Function* get_sqrt()
{
if (!sqrt_func)
{
std::vector<const Type*> args;
args.push_back(Type::DoubleTy);
FunctionType* sqrt_type =
FunctionType::get(Type::DoubleTy, args, false);
sqrt_func = M->getOrInsertFunction("sqrt",sqrt_type);
}
return sqrt_func;
}
/// @brief Return a Function* for the strlen libcall
Function* get_strcpy()
{
if (!strcpy_func)
{
std::vector<const Type*> args;
args.push_back(PointerType::get(Type::SByteTy));
args.push_back(PointerType::get(Type::SByteTy));
FunctionType* strcpy_type =
FunctionType::get(PointerType::get(Type::SByteTy), args, false);
strcpy_func = M->getOrInsertFunction("strcpy",strcpy_type);
}
return strcpy_func;
}
/// @brief Return a Function* for the strlen libcall
Function* get_strlen()
{
if (!strlen_func)
{
std::vector<const Type*> args;
args.push_back(PointerType::get(Type::SByteTy));
FunctionType* strlen_type =
FunctionType::get(TD->getIntPtrType(), args, false);
strlen_func = M->getOrInsertFunction("strlen",strlen_type);
}
return strlen_func;
}
/// @brief Return a Function* for the memchr libcall
Function* get_memchr()
{
if (!memchr_func)
{
std::vector<const Type*> args;
args.push_back(PointerType::get(Type::SByteTy));
args.push_back(Type::IntTy);
args.push_back(TD->getIntPtrType());
FunctionType* memchr_type = FunctionType::get(
PointerType::get(Type::SByteTy), args, false);
memchr_func = M->getOrInsertFunction("memchr",memchr_type);
}
return memchr_func;
}
/// @brief Return a Function* for the memcpy libcall
Function* get_memcpy() {
if (!memcpy_func) {
const Type *SBP = PointerType::get(Type::SByteTy);
memcpy_func = M->getOrInsertFunction("llvm.memcpy", Type::VoidTy,SBP, SBP,
Type::UIntTy, Type::UIntTy,
(Type *)0);
}
return memcpy_func;
}
Function* get_floorf() {
if (!floorf_func)
floorf_func = M->getOrInsertFunction("floorf", Type::FloatTy,
Type::FloatTy, (Type *)0);
return floorf_func;
}
private:
/// @brief Reset our cached data for a new Module
void reset(Module& mod)
{
M = &mod;
TD = &getAnalysis<TargetData>();
fputc_func = 0;
fwrite_func = 0;
memcpy_func = 0;
memchr_func = 0;
sqrt_func = 0;
strcpy_func = 0;
strlen_func = 0;
floorf_func = 0;
}
private:
Function* fputc_func; ///< Cached fputc function
Function* fwrite_func; ///< Cached fwrite function
Function* memcpy_func; ///< Cached llvm.memcpy function
Function* memchr_func; ///< Cached memchr function
Function* sqrt_func; ///< Cached sqrt function
Function* strcpy_func; ///< Cached strcpy function
Function* strlen_func; ///< Cached strlen function
Function* floorf_func; ///< Cached floorf function
Module* M; ///< Cached Module
TargetData* TD; ///< Cached TargetData
};
// Register the pass
RegisterOpt<SimplifyLibCalls>
X("simplify-libcalls","Simplify well-known library calls");
} // anonymous namespace
// The only public symbol in this file which just instantiates the pass object
ModulePass *llvm::createSimplifyLibCallsPass()
{
return new SimplifyLibCalls();
}
// Classes below here, in the anonymous namespace, are all subclasses of the
// LibCallOptimization class, each implementing all optimizations possible for a
// single well-known library call. Each has a static singleton instance that
// auto registers it into the "optlist" global above.
namespace {
// Forward declare utility functions.
bool getConstantStringLength(Value* V, uint64_t& len, ConstantArray** A = 0 );
Value *CastToCStr(Value *V, Instruction &IP);
/// This LibCallOptimization will find instances of a call to "exit" that occurs
/// within the "main" function and change it to a simple "ret" instruction with
/// the same value passed to the exit function. When this is done, it splits the
/// basic block at the exit(3) call and deletes the call instruction.
/// @brief Replace calls to exit in main with a simple return
struct ExitInMainOptimization : public LibCallOptimization
{
ExitInMainOptimization() : LibCallOptimization("exit",
"Number of 'exit' calls simplified") {}
// Make sure the called function looks like exit (int argument, int return
// type, external linkage, not varargs).
virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& SLC)
{
if (f->arg_size() >= 1)
if (f->arg_begin()->getType()->isInteger())
return true;
return false;
}
virtual bool OptimizeCall(CallInst* ci, SimplifyLibCalls& SLC)
{
// To be careful, we check that the call to exit is coming from "main", that
// main has external linkage, and the return type of main and the argument
// to exit have the same type.
Function *from = ci->getParent()->getParent();
if (from->hasExternalLinkage())
if (from->getReturnType() == ci->getOperand(1)->getType())
if (from->getName() == "main")
{
// Okay, time to actually do the optimization. First, get the basic
// block of the call instruction
BasicBlock* bb = ci->getParent();
// Create a return instruction that we'll replace the call with.
// Note that the argument of the return is the argument of the call
// instruction.
ReturnInst* ri = new ReturnInst(ci->getOperand(1), ci);
// Split the block at the call instruction which places it in a new
// basic block.
bb->splitBasicBlock(ci);
// The block split caused a branch instruction to be inserted into
// the end of the original block, right after the return instruction
// that we put there. That's not a valid block, so delete the branch
// instruction.
bb->getInstList().pop_back();
// Now we can finally get rid of the call instruction which now lives
// in the new basic block.
ci->eraseFromParent();
// Optimization succeeded, return true.
return true;
}
// We didn't pass the criteria for this optimization so return false
return false;
}
} ExitInMainOptimizer;
/// This LibCallOptimization will simplify a call to the strcat library
/// function. The simplification is possible only if the string being
/// concatenated is a constant array or a constant expression that results in
/// a constant string. In this case we can replace it with strlen + llvm.memcpy
/// of the constant string. Both of these calls are further reduced, if possible
/// on subsequent passes.
/// @brief Simplify the strcat library function.
struct StrCatOptimization : public LibCallOptimization
{
public:
/// @brief Default constructor
StrCatOptimization() : LibCallOptimization("strcat",
"Number of 'strcat' calls simplified") {}
public:
/// @brief Make sure that the "strcat" function has the right prototype
virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& SLC)
{
if (f->getReturnType() == PointerType::get(Type::SByteTy))
if (f->arg_size() == 2)
{
Function::const_arg_iterator AI = f->arg_begin();
if (AI++->getType() == PointerType::get(Type::SByteTy))
if (AI->getType() == PointerType::get(Type::SByteTy))
{
// Indicate this is a suitable call type.
return true;
}
}
return false;
}
/// @brief Optimize the strcat library function
virtual bool OptimizeCall(CallInst* ci, SimplifyLibCalls& SLC)
{
// Extract some information from the instruction
Module* M = ci->getParent()->getParent()->getParent();
Value* dest = ci->getOperand(1);
Value* src = ci->getOperand(2);
// Extract the initializer (while making numerous checks) from the
// source operand of the call to strcat. If we get null back, one of
// a variety of checks in get_GVInitializer failed
uint64_t len = 0;
if (!getConstantStringLength(src,len))
return false;
// Handle the simple, do-nothing case
if (len == 0)
{
ci->replaceAllUsesWith(dest);
ci->eraseFromParent();
return true;
}
// Increment the length because we actually want to memcpy the null
// terminator as well.
len++;
// We need to find the end of the destination string. That's where the
// memory is to be moved to. We just generate a call to strlen (further
// optimized in another pass). Note that the SLC.get_strlen() call
// caches the Function* for us.
CallInst* strlen_inst =
new CallInst(SLC.get_strlen(), dest, dest->getName()+".len",ci);
// Now that we have the destination's length, we must index into the
// destination's pointer to get the actual memcpy destination (end of
// the string .. we're concatenating).
std::vector<Value*> idx;
idx.push_back(strlen_inst);
GetElementPtrInst* gep =
new GetElementPtrInst(dest,idx,dest->getName()+".indexed",ci);
// We have enough information to now generate the memcpy call to
// do the concatenation for us.
std::vector<Value*> vals;
vals.push_back(gep); // destination
vals.push_back(ci->getOperand(2)); // source
vals.push_back(ConstantUInt::get(Type::UIntTy,len)); // length
vals.push_back(ConstantUInt::get(Type::UIntTy,1)); // alignment
new CallInst(SLC.get_memcpy(), vals, "", ci);
// Finally, substitute the first operand of the strcat call for the
// strcat call itself since strcat returns its first operand; and,
// kill the strcat CallInst.
ci->replaceAllUsesWith(dest);
ci->eraseFromParent();
return true;
}
} StrCatOptimizer;
/// This LibCallOptimization will simplify a call to the strchr library
/// function. It optimizes out cases where the arguments are both constant
/// and the result can be determined statically.
/// @brief Simplify the strcmp library function.
struct StrChrOptimization : public LibCallOptimization
{
public:
StrChrOptimization() : LibCallOptimization("strchr",
"Number of 'strchr' calls simplified") {}
/// @brief Make sure that the "strchr" function has the right prototype
virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& SLC)
{
if (f->getReturnType() == PointerType::get(Type::SByteTy) &&
f->arg_size() == 2)
return true;
return false;
}
/// @brief Perform the strchr optimizations
virtual bool OptimizeCall(CallInst* ci, SimplifyLibCalls& SLC)
{
// If there aren't three operands, bail
if (ci->getNumOperands() != 3)
return false;
// Check that the first argument to strchr is a constant array of sbyte.
// If it is, get the length and data, otherwise return false.
uint64_t len = 0;
ConstantArray* CA;
if (!getConstantStringLength(ci->getOperand(1),len,&CA))
return false;
// Check that the second argument to strchr is a constant int, return false
// if it isn't
ConstantSInt* CSI = dyn_cast<ConstantSInt>(ci->getOperand(2));
if (!CSI)
{
// Just lower this to memchr since we know the length of the string as
// it is constant.
Function* f = SLC.get_memchr();
std::vector<Value*> args;
args.push_back(ci->getOperand(1));
args.push_back(ci->getOperand(2));
args.push_back(ConstantUInt::get(SLC.getIntPtrType(),len));
ci->replaceAllUsesWith( new CallInst(f,args,ci->getName(),ci));
ci->eraseFromParent();
return true;
}
// Get the character we're looking for
int64_t chr = CSI->getValue();
// Compute the offset
uint64_t offset = 0;
bool char_found = false;
for (uint64_t i = 0; i < len; ++i)
{
if (ConstantSInt* CI = dyn_cast<ConstantSInt>(CA->getOperand(i)))
{
// Check for the null terminator
if (CI->isNullValue())
break; // we found end of string
else if (CI->getValue() == chr)
{
char_found = true;
offset = i;
break;
}
}
}
// strchr(s,c) -> offset_of_in(c,s)
// (if c is a constant integer and s is a constant string)
if (char_found)
{
std::vector<Value*> indices;
indices.push_back(ConstantUInt::get(Type::ULongTy,offset));
GetElementPtrInst* GEP = new GetElementPtrInst(ci->getOperand(1),indices,
ci->getOperand(1)->getName()+".strchr",ci);
ci->replaceAllUsesWith(GEP);
}
else
ci->replaceAllUsesWith(
ConstantPointerNull::get(PointerType::get(Type::SByteTy)));
ci->eraseFromParent();
return true;
}
} StrChrOptimizer;
/// This LibCallOptimization will simplify a call to the strcmp library
/// function. It optimizes out cases where one or both arguments are constant
/// and the result can be determined statically.
/// @brief Simplify the strcmp library function.
struct StrCmpOptimization : public LibCallOptimization
{
public:
StrCmpOptimization() : LibCallOptimization("strcmp",
"Number of 'strcmp' calls simplified") {}
/// @brief Make sure that the "strcmp" function has the right prototype
virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& SLC)
{
if (f->getReturnType() == Type::IntTy && f->arg_size() == 2)
return true;
return false;
}
/// @brief Perform the strcmp optimization
virtual bool OptimizeCall(CallInst* ci, SimplifyLibCalls& SLC)
{
// First, check to see if src and destination are the same. If they are,
// then the optimization is to replace the CallInst with a constant 0
// because the call is a no-op.
Value* s1 = ci->getOperand(1);
Value* s2 = ci->getOperand(2);
if (s1 == s2)
{
// strcmp(x,x) -> 0
ci->replaceAllUsesWith(ConstantInt::get(Type::IntTy,0));
ci->eraseFromParent();
return true;
}
bool isstr_1 = false;
uint64_t len_1 = 0;
ConstantArray* A1;
if (getConstantStringLength(s1,len_1,&A1))
{
isstr_1 = true;
if (len_1 == 0)
{
// strcmp("",x) -> *x
LoadInst* load =
new LoadInst(CastToCStr(s2,*ci), ci->getName()+".load",ci);
CastInst* cast =
new CastInst(load,Type::IntTy,ci->getName()+".int",ci);
ci->replaceAllUsesWith(cast);
ci->eraseFromParent();
return true;
}
}
bool isstr_2 = false;
uint64_t len_2 = 0;
ConstantArray* A2;
if (getConstantStringLength(s2,len_2,&A2))
{
isstr_2 = true;
if (len_2 == 0)
{
// strcmp(x,"") -> *x
LoadInst* load =
new LoadInst(CastToCStr(s1,*ci),ci->getName()+".val",ci);
CastInst* cast =
new CastInst(load,Type::IntTy,ci->getName()+".int",ci);
ci->replaceAllUsesWith(cast);
ci->eraseFromParent();
return true;
}
}
if (isstr_1 && isstr_2)
{
// strcmp(x,y) -> cnst (if both x and y are constant strings)
std::string str1 = A1->getAsString();
std::string str2 = A2->getAsString();
int result = strcmp(str1.c_str(), str2.c_str());
ci->replaceAllUsesWith(ConstantSInt::get(Type::IntTy,result));
ci->eraseFromParent();
return true;
}
return false;
}
} StrCmpOptimizer;
/// This LibCallOptimization will simplify a call to the strncmp library
/// function. It optimizes out cases where one or both arguments are constant
/// and the result can be determined statically.
/// @brief Simplify the strncmp library function.
struct StrNCmpOptimization : public LibCallOptimization
{
public:
StrNCmpOptimization() : LibCallOptimization("strncmp",
"Number of 'strncmp' calls simplified") {}
/// @brief Make sure that the "strncmp" function has the right prototype
virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& SLC)
{
if (f->getReturnType() == Type::IntTy && f->arg_size() == 3)
return true;
return false;
}
/// @brief Perform the strncpy optimization
virtual bool OptimizeCall(CallInst* ci, SimplifyLibCalls& SLC)
{
// First, check to see if src and destination are the same. If they are,
// then the optimization is to replace the CallInst with a constant 0
// because the call is a no-op.
Value* s1 = ci->getOperand(1);
Value* s2 = ci->getOperand(2);
if (s1 == s2)
{
// strncmp(x,x,l) -> 0
ci->replaceAllUsesWith(ConstantInt::get(Type::IntTy,0));
ci->eraseFromParent();
return true;
}
// Check the length argument, if it is Constant zero then the strings are
// considered equal.
uint64_t len_arg = 0;
bool len_arg_is_const = false;
if (ConstantInt* len_CI = dyn_cast<ConstantInt>(ci->getOperand(3)))
{
len_arg_is_const = true;
len_arg = len_CI->getRawValue();
if (len_arg == 0)
{
// strncmp(x,y,0) -> 0
ci->replaceAllUsesWith(ConstantInt::get(Type::IntTy,0));
ci->eraseFromParent();
return true;
}
}
bool isstr_1 = false;
uint64_t len_1 = 0;
ConstantArray* A1;
if (getConstantStringLength(s1,len_1,&A1))
{
isstr_1 = true;
if (len_1 == 0)
{
// strncmp("",x) -> *x
LoadInst* load = new LoadInst(s1,ci->getName()+".load",ci);
CastInst* cast =
new CastInst(load,Type::IntTy,ci->getName()+".int",ci);
ci->replaceAllUsesWith(cast);
ci->eraseFromParent();
return true;
}
}
bool isstr_2 = false;
uint64_t len_2 = 0;
ConstantArray* A2;
if (getConstantStringLength(s2,len_2,&A2))
{
isstr_2 = true;
if (len_2 == 0)
{
// strncmp(x,"") -> *x
LoadInst* load = new LoadInst(s2,ci->getName()+".val",ci);
CastInst* cast =
new CastInst(load,Type::IntTy,ci->getName()+".int",ci);
ci->replaceAllUsesWith(cast);
ci->eraseFromParent();
return true;
}
}
if (isstr_1 && isstr_2 && len_arg_is_const)
{
// strncmp(x,y,const) -> constant
std::string str1 = A1->getAsString();
std::string str2 = A2->getAsString();
int result = strncmp(str1.c_str(), str2.c_str(), len_arg);
ci->replaceAllUsesWith(ConstantSInt::get(Type::IntTy,result));
ci->eraseFromParent();
return true;
}
return false;
}
} StrNCmpOptimizer;
/// This LibCallOptimization will simplify a call to the strcpy library
/// function. Two optimizations are possible:
/// (1) If src and dest are the same and not volatile, just return dest
/// (2) If the src is a constant then we can convert to llvm.memmove
/// @brief Simplify the strcpy library function.
struct StrCpyOptimization : public LibCallOptimization
{
public:
StrCpyOptimization() : LibCallOptimization("strcpy",
"Number of 'strcpy' calls simplified") {}
/// @brief Make sure that the "strcpy" function has the right prototype
virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& SLC)
{
if (f->getReturnType() == PointerType::get(Type::SByteTy))
if (f->arg_size() == 2)
{
Function::const_arg_iterator AI = f->arg_begin();
if (AI++->getType() == PointerType::get(Type::SByteTy))
if (AI->getType() == PointerType::get(Type::SByteTy))
{
// Indicate this is a suitable call type.
return true;
}
}
return false;
}
/// @brief Perform the strcpy optimization
virtual bool OptimizeCall(CallInst* ci, SimplifyLibCalls& SLC)
{
// First, check to see if src and destination are the same. If they are,
// then the optimization is to replace the CallInst with the destination
// because the call is a no-op. Note that this corresponds to the
// degenerate strcpy(X,X) case which should have "undefined" results
// according to the C specification. However, it occurs sometimes and
// we optimize it as a no-op.
Value* dest = ci->getOperand(1);
Value* src = ci->getOperand(2);
if (dest == src)
{
ci->replaceAllUsesWith(dest);
ci->eraseFromParent();
return true;
}
// Get the length of the constant string referenced by the second operand,
// the "src" parameter. Fail the optimization if we can't get the length
// (note that getConstantStringLength does lots of checks to make sure this
// is valid).
uint64_t len = 0;
if (!getConstantStringLength(ci->getOperand(2),len))
return false;
// If the constant string's length is zero we can optimize this by just
// doing a store of 0 at the first byte of the destination
if (len == 0)
{
new StoreInst(ConstantInt::get(Type::SByteTy,0),ci->getOperand(1),ci);
ci->replaceAllUsesWith(dest);
ci->eraseFromParent();
return true;
}
// Increment the length because we actually want to memcpy the null
// terminator as well.
len++;
// Extract some information from the instruction
Module* M = ci->getParent()->getParent()->getParent();
// We have enough information to now generate the memcpy call to
// do the concatenation for us.
std::vector<Value*> vals;
vals.push_back(dest); // destination
vals.push_back(src); // source
vals.push_back(ConstantUInt::get(Type::UIntTy,len)); // length
vals.push_back(ConstantUInt::get(Type::UIntTy,1)); // alignment
new CallInst(SLC.get_memcpy(), vals, "", ci);
// Finally, substitute the first operand of the strcat call for the
// strcat call itself since strcat returns its first operand; and,
// kill the strcat CallInst.
ci->replaceAllUsesWith(dest);
ci->eraseFromParent();
return true;
}
} StrCpyOptimizer;
/// This LibCallOptimization will simplify a call to the strlen library
/// function by replacing it with a constant value if the string provided to
/// it is a constant array.
/// @brief Simplify the strlen library function.
struct StrLenOptimization : public LibCallOptimization
{
StrLenOptimization() : LibCallOptimization("strlen",
"Number of 'strlen' calls simplified") {}
/// @brief Make sure that the "strlen" function has the right prototype
virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& SLC)
{
if (f->getReturnType() == SLC.getTargetData()->getIntPtrType())
if (f->arg_size() == 1)
if (Function::const_arg_iterator AI = f->arg_begin())
if (AI->getType() == PointerType::get(Type::SByteTy))
return true;
return false;
}
/// @brief Perform the strlen optimization
virtual bool OptimizeCall(CallInst* ci, SimplifyLibCalls& SLC)
{
// Make sure we're dealing with an sbyte* here.
Value* str = ci->getOperand(1);
if (str->getType() != PointerType::get(Type::SByteTy))
return false;
// Does the call to strlen have exactly one use?
if (ci->hasOneUse())
// Is that single use a binary operator?
if (BinaryOperator* bop = dyn_cast<BinaryOperator>(ci->use_back()))
// Is it compared against a constant integer?
if (ConstantInt* CI = dyn_cast<ConstantInt>(bop->getOperand(1)))
{
// Get the value the strlen result is compared to
uint64_t val = CI->getRawValue();
// If its compared against length 0 with == or !=
if (val == 0 &&
(bop->getOpcode() == Instruction::SetEQ ||
bop->getOpcode() == Instruction::SetNE))
{
// strlen(x) != 0 -> *x != 0
// strlen(x) == 0 -> *x == 0
LoadInst* load = new LoadInst(str,str->getName()+".first",ci);
BinaryOperator* rbop = BinaryOperator::create(bop->getOpcode(),
load, ConstantSInt::get(Type::SByteTy,0),
bop->getName()+".strlen", ci);
bop->replaceAllUsesWith(rbop);
bop->eraseFromParent();
ci->eraseFromParent();
return true;
}
}
// Get the length of the constant string operand
uint64_t len = 0;
if (!getConstantStringLength(ci->getOperand(1),len))
return false;
// strlen("xyz") -> 3 (for example)
const Type *Ty = SLC.getTargetData()->getIntPtrType();
if (Ty->isSigned())
ci->replaceAllUsesWith(ConstantSInt::get(Ty, len));
else
ci->replaceAllUsesWith(ConstantUInt::get(Ty, len));
ci->eraseFromParent();
return true;
}
} StrLenOptimizer;
/// IsOnlyUsedInEqualsComparison - Return true if it only matters that the value
/// is equal or not-equal to zero.
static bool IsOnlyUsedInEqualsZeroComparison(Instruction *I) {
for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
UI != E; ++UI) {
Instruction *User = cast<Instruction>(*UI);
if (User->getOpcode() == Instruction::SetNE ||
User->getOpcode() == Instruction::SetEQ) {
if (isa<Constant>(User->getOperand(1)) &&
cast<Constant>(User->getOperand(1))->isNullValue())
continue;
} else if (CastInst *CI = dyn_cast<CastInst>(User))
if (CI->getType() == Type::BoolTy)
continue;
// Unknown instruction.
return false;
}
return true;
}
/// This memcmpOptimization will simplify a call to the memcmp library
/// function.
struct memcmpOptimization : public LibCallOptimization {
/// @brief Default Constructor
memcmpOptimization()
: LibCallOptimization("memcmp", "Number of 'memcmp' calls simplified") {}
/// @brief Make sure that the "memcmp" function has the right prototype
virtual bool ValidateCalledFunction(const Function *F, SimplifyLibCalls &TD) {
Function::const_arg_iterator AI = F->arg_begin();
if (F->arg_size() != 3 || !isa<PointerType>(AI->getType())) return false;
if (!isa<PointerType>((++AI)->getType())) return false;
if (!(++AI)->getType()->isInteger()) return false;
if (!F->getReturnType()->isInteger()) return false;
return true;
}
/// Because of alignment and instruction information that we don't have, we
/// leave the bulk of this to the code generators.
///
/// Note that we could do much more if we could force alignment on otherwise
/// small aligned allocas, or if we could indicate that loads have a small
/// alignment.
virtual bool OptimizeCall(CallInst *CI, SimplifyLibCalls &TD) {
Value *LHS = CI->getOperand(1), *RHS = CI->getOperand(2);
// If the two operands are the same, return zero.
if (LHS == RHS) {
// memcmp(s,s,x) -> 0
CI->replaceAllUsesWith(Constant::getNullValue(CI->getType()));
CI->eraseFromParent();
return true;
}
// Make sure we have a constant length.
ConstantInt *LenC = dyn_cast<ConstantInt>(CI->getOperand(3));
if (!LenC) return false;
uint64_t Len = LenC->getRawValue();
// If the length is zero, this returns 0.
switch (Len) {
case 0:
// memcmp(s1,s2,0) -> 0
CI->replaceAllUsesWith(Constant::getNullValue(CI->getType()));
CI->eraseFromParent();
return true;
case 1: {
// memcmp(S1,S2,1) -> *(ubyte*)S1 - *(ubyte*)S2
const Type *UCharPtr = PointerType::get(Type::UByteTy);
CastInst *Op1Cast = new CastInst(LHS, UCharPtr, LHS->getName(), CI);
CastInst *Op2Cast = new CastInst(RHS, UCharPtr, RHS->getName(), CI);
Value *S1V = new LoadInst(Op1Cast, LHS->getName()+".val", CI);
Value *S2V = new LoadInst(Op2Cast, RHS->getName()+".val", CI);
Value *RV = BinaryOperator::createSub(S1V, S2V, CI->getName()+".diff",CI);
if (RV->getType() != CI->getType())
RV = new CastInst(RV, CI->getType(), RV->getName(), CI);
CI->replaceAllUsesWith(RV);
CI->eraseFromParent();
return true;
}
case 2:
if (IsOnlyUsedInEqualsZeroComparison(CI)) {
// TODO: IF both are aligned, use a short load/compare.
// memcmp(S1,S2,2) -> S1[0]-S2[0] | S1[1]-S2[1] iff only ==/!= 0 matters
const Type *UCharPtr = PointerType::get(Type::UByteTy);
CastInst *Op1Cast = new CastInst(LHS, UCharPtr, LHS->getName(), CI);
CastInst *Op2Cast = new CastInst(RHS, UCharPtr, RHS->getName(), CI);
Value *S1V1 = new LoadInst(Op1Cast, LHS->getName()+".val1", CI);
Value *S2V1 = new LoadInst(Op2Cast, RHS->getName()+".val1", CI);
Value *D1 = BinaryOperator::createSub(S1V1, S2V1,
CI->getName()+".d1", CI);
Constant *One = ConstantInt::get(Type::IntTy, 1);
Value *G1 = new GetElementPtrInst(Op1Cast, One, "next1v", CI);
Value *G2 = new GetElementPtrInst(Op2Cast, One, "next2v", CI);
Value *S1V2 = new LoadInst(G1, LHS->getName()+".val2", CI);
Value *S2V2 = new LoadInst(G1, RHS->getName()+".val2", CI);
Value *D2 = BinaryOperator::createSub(S1V2, S2V2,
CI->getName()+".d1", CI);
Value *Or = BinaryOperator::createOr(D1, D2, CI->getName()+".res", CI);
if (Or->getType() != CI->getType())
Or = new CastInst(Or, CI->getType(), Or->getName(), CI);
CI->replaceAllUsesWith(Or);
CI->eraseFromParent();
return true;
}
break;
default:
break;
}
return false;
}
} memcmpOptimizer;
/// This LibCallOptimization will simplify a call to the memcpy library
/// function by expanding it out to a single store of size 0, 1, 2, 4, or 8
/// bytes depending on the length of the string and the alignment. Additional
/// optimizations are possible in code generation (sequence of immediate store)
/// @brief Simplify the memcpy library function.
struct LLVMMemCpyOptimization : public LibCallOptimization
{
/// @brief Default Constructor
LLVMMemCpyOptimization() : LibCallOptimization("llvm.memcpy",
"Number of 'llvm.memcpy' calls simplified") {}
protected:
/// @brief Subclass Constructor
LLVMMemCpyOptimization(const char* fname, const char* desc)
: LibCallOptimization(fname, desc) {}
public:
/// @brief Make sure that the "memcpy" function has the right prototype
virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& TD)
{
// Just make sure this has 4 arguments per LLVM spec.
return (f->arg_size() == 4);
}
/// Because of alignment and instruction information that we don't have, we
/// leave the bulk of this to the code generators. The optimization here just
/// deals with a few degenerate cases where the length of the string and the
/// alignment match the sizes of our intrinsic types so we can do a load and
/// store instead of the memcpy call.
/// @brief Perform the memcpy optimization.
virtual bool OptimizeCall(CallInst* ci, SimplifyLibCalls& TD)
{
// Make sure we have constant int values to work with
ConstantInt* LEN = dyn_cast<ConstantInt>(ci->getOperand(3));
if (!LEN)
return false;
ConstantInt* ALIGN = dyn_cast<ConstantInt>(ci->getOperand(4));
if (!ALIGN)
return false;
// If the length is larger than the alignment, we can't optimize
uint64_t len = LEN->getRawValue();
uint64_t alignment = ALIGN->getRawValue();
if (alignment == 0)
alignment = 1; // Alignment 0 is identity for alignment 1
if (len > alignment)
return false;
// Get the type we will cast to, based on size of the string
Value* dest = ci->getOperand(1);
Value* src = ci->getOperand(2);
Type* castType = 0;
switch (len)
{
case 0:
// memcpy(d,s,0,a) -> noop
ci->eraseFromParent();
return true;
case 1: castType = Type::SByteTy; break;
case 2: castType = Type::ShortTy; break;
case 4: castType = Type::IntTy; break;
case 8: castType = Type::LongTy; break;
default:
return false;
}
// Cast source and dest to the right sized primitive and then load/store
CastInst* SrcCast =
new CastInst(src,PointerType::get(castType),src->getName()+".cast",ci);
CastInst* DestCast =
new CastInst(dest,PointerType::get(castType),dest->getName()+".cast",ci);
LoadInst* LI = new LoadInst(SrcCast,SrcCast->getName()+".val",ci);
StoreInst* SI = new StoreInst(LI, DestCast, ci);
ci->eraseFromParent();
return true;
}
} LLVMMemCpyOptimizer;
/// This LibCallOptimization will simplify a call to the memmove library
/// function. It is identical to MemCopyOptimization except for the name of
/// the intrinsic.
/// @brief Simplify the memmove library function.
struct LLVMMemMoveOptimization : public LLVMMemCpyOptimization
{
/// @brief Default Constructor
LLVMMemMoveOptimization() : LLVMMemCpyOptimization("llvm.memmove",
"Number of 'llvm.memmove' calls simplified") {}
} LLVMMemMoveOptimizer;
/// This LibCallOptimization will simplify a call to the memset library
/// function by expanding it out to a single store of size 0, 1, 2, 4, or 8
/// bytes depending on the length argument.
struct LLVMMemSetOptimization : public LibCallOptimization
{
/// @brief Default Constructor
LLVMMemSetOptimization() : LibCallOptimization("llvm.memset",
"Number of 'llvm.memset' calls simplified") {}
public:
/// @brief Make sure that the "memset" function has the right prototype
virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& TD)
{
// Just make sure this has 3 arguments per LLVM spec.
return (f->arg_size() == 4);
}
/// Because of alignment and instruction information that we don't have, we
/// leave the bulk of this to the code generators. The optimization here just
/// deals with a few degenerate cases where the length parameter is constant
/// and the alignment matches the sizes of our intrinsic types so we can do
/// store instead of the memcpy call. Other calls are transformed into the
/// llvm.memset intrinsic.
/// @brief Perform the memset optimization.
virtual bool OptimizeCall(CallInst* ci, SimplifyLibCalls& TD)
{
// Make sure we have constant int values to work with
ConstantInt* LEN = dyn_cast<ConstantInt>(ci->getOperand(3));
if (!LEN)
return false;
ConstantInt* ALIGN = dyn_cast<ConstantInt>(ci->getOperand(4));
if (!ALIGN)
return false;
// Extract the length and alignment
uint64_t len = LEN->getRawValue();
uint64_t alignment = ALIGN->getRawValue();
// Alignment 0 is identity for alignment 1
if (alignment == 0)
alignment = 1;
// If the length is zero, this is a no-op
if (len == 0)
{
// memset(d,c,0,a) -> noop
ci->eraseFromParent();
return true;
}
// If the length is larger than the alignment, we can't optimize
if (len > alignment)
return false;
// Make sure we have a constant ubyte to work with so we can extract
// the value to be filled.
ConstantUInt* FILL = dyn_cast<ConstantUInt>(ci->getOperand(2));
if (!FILL)
return false;
if (FILL->getType() != Type::UByteTy)
return false;
// memset(s,c,n) -> store s, c (for n=1,2,4,8)
// Extract the fill character
uint64_t fill_char = FILL->getValue();
uint64_t fill_value = fill_char;
// Get the type we will cast to, based on size of memory area to fill, and
// and the value we will store there.
Value* dest = ci->getOperand(1);
Type* castType = 0;
switch (len)
{
case 1:
castType = Type::UByteTy;
break;
case 2:
castType = Type::UShortTy;
fill_value |= fill_char << 8;
break;
case 4:
castType = Type::UIntTy;
fill_value |= fill_char << 8 | fill_char << 16 | fill_char << 24;
break;
case 8:
castType = Type::ULongTy;
fill_value |= fill_char << 8 | fill_char << 16 | fill_char << 24;
fill_value |= fill_char << 32 | fill_char << 40 | fill_char << 48;
fill_value |= fill_char << 56;
break;
default:
return false;
}
// Cast dest to the right sized primitive and then load/store
CastInst* DestCast =
new CastInst(dest,PointerType::get(castType),dest->getName()+".cast",ci);
new StoreInst(ConstantUInt::get(castType,fill_value),DestCast, ci);
ci->eraseFromParent();
return true;
}
} LLVMMemSetOptimizer;
/// This LibCallOptimization will simplify calls to the "pow" library
/// function. It looks for cases where the result of pow is well known and
/// substitutes the appropriate value.
/// @brief Simplify the pow library function.
struct PowOptimization : public LibCallOptimization
{
public:
/// @brief Default Constructor
PowOptimization() : LibCallOptimization("pow",
"Number of 'pow' calls simplified") {}
/// @brief Make sure that the "pow" function has the right prototype
virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& SLC)
{
// Just make sure this has 2 arguments
return (f->arg_size() == 2);
}
/// @brief Perform the pow optimization.
virtual bool OptimizeCall(CallInst* ci, SimplifyLibCalls& SLC)
{
const Type *Ty = cast<Function>(ci->getOperand(0))->getReturnType();
Value* base = ci->getOperand(1);
Value* expn = ci->getOperand(2);
if (ConstantFP *Op1 = dyn_cast<ConstantFP>(base)) {
double Op1V = Op1->getValue();
if (Op1V == 1.0)
{
// pow(1.0,x) -> 1.0
ci->replaceAllUsesWith(ConstantFP::get(Ty,1.0));
ci->eraseFromParent();
return true;
}
}
else if (ConstantFP* Op2 = dyn_cast<ConstantFP>(expn))
{
double Op2V = Op2->getValue();
if (Op2V == 0.0)
{
// pow(x,0.0) -> 1.0
ci->replaceAllUsesWith(ConstantFP::get(Ty,1.0));
ci->eraseFromParent();
return true;
}
else if (Op2V == 0.5)
{
// pow(x,0.5) -> sqrt(x)
CallInst* sqrt_inst = new CallInst(SLC.get_sqrt(), base,
ci->getName()+".pow",ci);
ci->replaceAllUsesWith(sqrt_inst);
ci->eraseFromParent();
return true;
}
else if (Op2V == 1.0)
{
// pow(x,1.0) -> x
ci->replaceAllUsesWith(base);
ci->eraseFromParent();
return true;
}
else if (Op2V == -1.0)
{
// pow(x,-1.0) -> 1.0/x
BinaryOperator* div_inst= BinaryOperator::createDiv(
ConstantFP::get(Ty,1.0), base, ci->getName()+".pow", ci);
ci->replaceAllUsesWith(div_inst);
ci->eraseFromParent();
return true;
}
}
return false; // opt failed
}
} PowOptimizer;
/// This LibCallOptimization will simplify calls to the "fprintf" library
/// function. It looks for cases where the result of fprintf is not used and the
/// operation can be reduced to something simpler.
/// @brief Simplify the pow library function.
struct FPrintFOptimization : public LibCallOptimization
{
public:
/// @brief Default Constructor
FPrintFOptimization() : LibCallOptimization("fprintf",
"Number of 'fprintf' calls simplified") {}
/// @brief Make sure that the "fprintf" function has the right prototype
virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& SLC)
{
// Just make sure this has at least 2 arguments
return (f->arg_size() >= 2);
}
/// @brief Perform the fprintf optimization.
virtual bool OptimizeCall(CallInst* ci, SimplifyLibCalls& SLC)
{
// If the call has more than 3 operands, we can't optimize it
if (ci->getNumOperands() > 4 || ci->getNumOperands() <= 2)
return false;
// If the result of the fprintf call is used, none of these optimizations
// can be made.
if (!ci->use_empty())
return false;
// All the optimizations depend on the length of the second argument and the
// fact that it is a constant string array. Check that now
uint64_t len = 0;
ConstantArray* CA = 0;
if (!getConstantStringLength(ci->getOperand(2), len, &CA))
return false;
if (ci->getNumOperands() == 3)
{
// Make sure there's no % in the constant array
for (unsigned i = 0; i < len; ++i)
{
if (ConstantInt* CI = dyn_cast<ConstantInt>(CA->getOperand(i)))
{
// Check for the null terminator
if (CI->getRawValue() == '%')
return false; // we found end of string
}
else
return false;
}
// fprintf(file,fmt) -> fwrite(fmt,strlen(fmt),file)
const Type* FILEptr_type = ci->getOperand(1)->getType();
Function* fwrite_func = SLC.get_fwrite(FILEptr_type);
if (!fwrite_func)
return false;
// Make sure that the fprintf() and fwrite() functions both take the
// same type of char pointer.
if (ci->getOperand(2)->getType() !=
fwrite_func->getFunctionType()->getParamType(0))
return false;
std::vector<Value*> args;
args.push_back(ci->getOperand(2));
args.push_back(ConstantUInt::get(SLC.getIntPtrType(),len));
args.push_back(ConstantUInt::get(SLC.getIntPtrType(),1));
args.push_back(ci->getOperand(1));
new CallInst(fwrite_func,args,ci->getName(),ci);
ci->replaceAllUsesWith(ConstantSInt::get(Type::IntTy,len));
ci->eraseFromParent();
return true;
}
// The remaining optimizations require the format string to be length 2
// "%s" or "%c".
if (len != 2)
return false;
// The first character has to be a %
if (ConstantInt* CI = dyn_cast<ConstantInt>(CA->getOperand(0)))
if (CI->getRawValue() != '%')
return false;
// Get the second character and switch on its value
ConstantInt* CI = dyn_cast<ConstantInt>(CA->getOperand(1));
switch (CI->getRawValue())
{
case 's':
{
uint64_t len = 0;
ConstantArray* CA = 0;
if (!getConstantStringLength(ci->getOperand(3), len, &CA))
return false;
// fprintf(file,"%s",str) -> fwrite(fmt,strlen(fmt),1,file)
const Type* FILEptr_type = ci->getOperand(1)->getType();
Function* fwrite_func = SLC.get_fwrite(FILEptr_type);
if (!fwrite_func)
return false;
std::vector<Value*> args;
args.push_back(CastToCStr(ci->getOperand(3), *ci));
args.push_back(ConstantUInt::get(SLC.getIntPtrType(),len));
args.push_back(ConstantUInt::get(SLC.getIntPtrType(),1));
args.push_back(ci->getOperand(1));
new CallInst(fwrite_func,args,ci->getName(),ci);
ci->replaceAllUsesWith(ConstantSInt::get(Type::IntTy,len));
break;
}
case 'c':
{
ConstantInt* CI = dyn_cast<ConstantInt>(ci->getOperand(3));
if (!CI)
return false;
const Type* FILEptr_type = ci->getOperand(1)->getType();
Function* fputc_func = SLC.get_fputc(FILEptr_type);
if (!fputc_func)
return false;
CastInst* cast = new CastInst(CI,Type::IntTy,CI->getName()+".int",ci);
new CallInst(fputc_func,cast,ci->getOperand(1),"",ci);
ci->replaceAllUsesWith(ConstantSInt::get(Type::IntTy,1));
break;
}
default:
return false;
}
ci->eraseFromParent();
return true;
}
} FPrintFOptimizer;
/// This LibCallOptimization will simplify calls to the "sprintf" library
/// function. It looks for cases where the result of sprintf is not used and the
/// operation can be reduced to something simpler.
/// @brief Simplify the pow library function.
struct SPrintFOptimization : public LibCallOptimization
{
public:
/// @brief Default Constructor
SPrintFOptimization() : LibCallOptimization("sprintf",
"Number of 'sprintf' calls simplified") {}
/// @brief Make sure that the "fprintf" function has the right prototype
virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& SLC)
{
// Just make sure this has at least 2 arguments
return (f->getReturnType() == Type::IntTy && f->arg_size() >= 2);
}
/// @brief Perform the sprintf optimization.
virtual bool OptimizeCall(CallInst* ci, SimplifyLibCalls& SLC)
{
// If the call has more than 3 operands, we can't optimize it
if (ci->getNumOperands() > 4 || ci->getNumOperands() < 3)
return false;
// All the optimizations depend on the length of the second argument and the
// fact that it is a constant string array. Check that now
uint64_t len = 0;
ConstantArray* CA = 0;
if (!getConstantStringLength(ci->getOperand(2), len, &CA))
return false;
if (ci->getNumOperands() == 3)
{
if (len == 0)
{
// If the length is 0, we just need to store a null byte
new StoreInst(ConstantInt::get(Type::SByteTy,0),ci->getOperand(1),ci);
ci->replaceAllUsesWith(ConstantSInt::get(Type::IntTy,0));
ci->eraseFromParent();
return true;
}
// Make sure there's no % in the constant array
for (unsigned i = 0; i < len; ++i)
{
if (ConstantInt* CI = dyn_cast<ConstantInt>(CA->getOperand(i)))
{
// Check for the null terminator
if (CI->getRawValue() == '%')
return false; // we found a %, can't optimize
}
else
return false; // initializer is not constant int, can't optimize
}
// Increment length because we want to copy the null byte too
len++;
// sprintf(str,fmt) -> llvm.memcpy(str,fmt,strlen(fmt),1)
Function* memcpy_func = SLC.get_memcpy();
if (!memcpy_func)
return false;
std::vector<Value*> args;
args.push_back(ci->getOperand(1));
args.push_back(ci->getOperand(2));
args.push_back(ConstantUInt::get(Type::UIntTy,len));
args.push_back(ConstantUInt::get(Type::UIntTy,1));
new CallInst(memcpy_func,args,"",ci);
ci->replaceAllUsesWith(ConstantSInt::get(Type::IntTy,len));
ci->eraseFromParent();
return true;
}
// The remaining optimizations require the format string to be length 2
// "%s" or "%c".
if (len != 2)
return false;
// The first character has to be a %
if (ConstantInt* CI = dyn_cast<ConstantInt>(CA->getOperand(0)))
if (CI->getRawValue() != '%')
return false;
// Get the second character and switch on its value
ConstantInt* CI = dyn_cast<ConstantInt>(CA->getOperand(1));
switch (CI->getRawValue()) {
case 's': {
// sprintf(dest,"%s",str) -> llvm.memcpy(dest, str, strlen(str)+1, 1)
Function* strlen_func = SLC.get_strlen();
Function* memcpy_func = SLC.get_memcpy();
if (!strlen_func || !memcpy_func)
return false;
Value *Len = new CallInst(strlen_func, CastToCStr(ci->getOperand(3), *ci),
ci->getOperand(3)->getName()+".len", ci);
Value *Len1 = BinaryOperator::createAdd(Len,
ConstantInt::get(Len->getType(), 1),
Len->getName()+"1", ci);
if (Len1->getType() != Type::UIntTy)
Len1 = new CastInst(Len1, Type::UIntTy, Len1->getName(), ci);
std::vector<Value*> args;
args.push_back(CastToCStr(ci->getOperand(1), *ci));
args.push_back(CastToCStr(ci->getOperand(3), *ci));
args.push_back(Len1);
args.push_back(ConstantUInt::get(Type::UIntTy,1));
new CallInst(memcpy_func, args, "", ci);
// The strlen result is the unincremented number of bytes in the string.
if (!ci->use_empty()) {
if (Len->getType() != ci->getType())
Len = new CastInst(Len, ci->getType(), Len->getName(), ci);
ci->replaceAllUsesWith(Len);
}
ci->eraseFromParent();
return true;
}
case 'c': {
// sprintf(dest,"%c",chr) -> store chr, dest
CastInst* cast = new CastInst(ci->getOperand(3),Type::SByteTy,"char",ci);
new StoreInst(cast, ci->getOperand(1), ci);
GetElementPtrInst* gep = new GetElementPtrInst(ci->getOperand(1),
ConstantUInt::get(Type::UIntTy,1),ci->getOperand(1)->getName()+".end",
ci);
new StoreInst(ConstantInt::get(Type::SByteTy,0),gep,ci);
ci->replaceAllUsesWith(ConstantSInt::get(Type::IntTy,1));
ci->eraseFromParent();
return true;
}
}
return false;
}
} SPrintFOptimizer;
/// This LibCallOptimization will simplify calls to the "fputs" library
/// function. It looks for cases where the result of fputs is not used and the
/// operation can be reduced to something simpler.
/// @brief Simplify the pow library function.
struct PutsOptimization : public LibCallOptimization
{
public:
/// @brief Default Constructor
PutsOptimization() : LibCallOptimization("fputs",
"Number of 'fputs' calls simplified") {}
/// @brief Make sure that the "fputs" function has the right prototype
virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& SLC)
{
// Just make sure this has 2 arguments
return (f->arg_size() == 2);
}
/// @brief Perform the fputs optimization.
virtual bool OptimizeCall(CallInst* ci, SimplifyLibCalls& SLC)
{
// If the result is used, none of these optimizations work
if (!ci->use_empty())
return false;
// All the optimizations depend on the length of the first argument and the
// fact that it is a constant string array. Check that now
uint64_t len = 0;
if (!getConstantStringLength(ci->getOperand(1), len))
return false;
switch (len)
{
case 0:
// fputs("",F) -> noop
break;
case 1:
{
// fputs(s,F) -> fputc(s[0],F) (if s is constant and strlen(s) == 1)
const Type* FILEptr_type = ci->getOperand(2)->getType();
Function* fputc_func = SLC.get_fputc(FILEptr_type);
if (!fputc_func)
return false;
LoadInst* loadi = new LoadInst(ci->getOperand(1),
ci->getOperand(1)->getName()+".byte",ci);
CastInst* casti = new CastInst(loadi,Type::IntTy,
loadi->getName()+".int",ci);
new CallInst(fputc_func,casti,ci->getOperand(2),"",ci);
break;
}
default:
{
// fputs(s,F) -> fwrite(s,1,len,F) (if s is constant and strlen(s) > 1)
const Type* FILEptr_type = ci->getOperand(2)->getType();
Function* fwrite_func = SLC.get_fwrite(FILEptr_type);
if (!fwrite_func)
return false;
std::vector<Value*> parms;
parms.push_back(ci->getOperand(1));
parms.push_back(ConstantUInt::get(SLC.getIntPtrType(),len));
parms.push_back(ConstantUInt::get(SLC.getIntPtrType(),1));
parms.push_back(ci->getOperand(2));
new CallInst(fwrite_func,parms,"",ci);
break;
}
}
ci->eraseFromParent();
return true; // success
}
} PutsOptimizer;
/// This LibCallOptimization will simplify calls to the "isdigit" library
/// function. It simply does range checks the parameter explicitly.
/// @brief Simplify the isdigit library function.
struct isdigitOptimization : public LibCallOptimization {
public:
isdigitOptimization() : LibCallOptimization("isdigit",
"Number of 'isdigit' calls simplified") {}
/// @brief Make sure that the "isdigit" function has the right prototype
virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& SLC)
{
// Just make sure this has 1 argument
return (f->arg_size() == 1);
}
/// @brief Perform the toascii optimization.
virtual bool OptimizeCall(CallInst* ci, SimplifyLibCalls& SLC)
{
if (ConstantInt* CI = dyn_cast<ConstantInt>(ci->getOperand(1)))
{
// isdigit(c) -> 0 or 1, if 'c' is constant
uint64_t val = CI->getRawValue();
if (val >= '0' && val <='9')
ci->replaceAllUsesWith(ConstantSInt::get(Type::IntTy,1));
else
ci->replaceAllUsesWith(ConstantSInt::get(Type::IntTy,0));
ci->eraseFromParent();
return true;
}
// isdigit(c) -> (unsigned)c - '0' <= 9
CastInst* cast =
new CastInst(ci->getOperand(1),Type::UIntTy,
ci->getOperand(1)->getName()+".uint",ci);
BinaryOperator* sub_inst = BinaryOperator::createSub(cast,
ConstantUInt::get(Type::UIntTy,0x30),
ci->getOperand(1)->getName()+".sub",ci);
SetCondInst* setcond_inst = new SetCondInst(Instruction::SetLE,sub_inst,
ConstantUInt::get(Type::UIntTy,9),
ci->getOperand(1)->getName()+".cmp",ci);
CastInst* c2 =
new CastInst(setcond_inst,Type::IntTy,
ci->getOperand(1)->getName()+".isdigit",ci);
ci->replaceAllUsesWith(c2);
ci->eraseFromParent();
return true;
}
} isdigitOptimizer;
struct isasciiOptimization : public LibCallOptimization {
public:
isasciiOptimization()
: LibCallOptimization("isascii", "Number of 'isascii' calls simplified") {}
virtual bool ValidateCalledFunction(const Function *F, SimplifyLibCalls &SLC){
return F->arg_size() == 1 && F->arg_begin()->getType()->isInteger() &&
F->getReturnType()->isInteger();
}
/// @brief Perform the isascii optimization.
virtual bool OptimizeCall(CallInst *CI, SimplifyLibCalls &SLC) {
// isascii(c) -> (unsigned)c < 128
Value *V = CI->getOperand(1);
if (V->getType()->isSigned())
V = new CastInst(V, V->getType()->getUnsignedVersion(), V->getName(), CI);
Value *Cmp = BinaryOperator::createSetLT(V, ConstantUInt::get(V->getType(),
128),
V->getName()+".isascii", CI);
if (Cmp->getType() != CI->getType())
Cmp = new CastInst(Cmp, CI->getType(), Cmp->getName(), CI);
CI->replaceAllUsesWith(Cmp);
CI->eraseFromParent();
return true;
}
} isasciiOptimizer;
/// This LibCallOptimization will simplify calls to the "toascii" library
/// function. It simply does the corresponding and operation to restrict the
/// range of values to the ASCII character set (0-127).
/// @brief Simplify the toascii library function.
struct ToAsciiOptimization : public LibCallOptimization
{
public:
/// @brief Default Constructor
ToAsciiOptimization() : LibCallOptimization("toascii",
"Number of 'toascii' calls simplified") {}
/// @brief Make sure that the "fputs" function has the right prototype
virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& SLC)
{
// Just make sure this has 2 arguments
return (f->arg_size() == 1);
}
/// @brief Perform the toascii optimization.
virtual bool OptimizeCall(CallInst* ci, SimplifyLibCalls& SLC)
{
// toascii(c) -> (c & 0x7f)
Value* chr = ci->getOperand(1);
BinaryOperator* and_inst = BinaryOperator::createAnd(chr,
ConstantInt::get(chr->getType(),0x7F),ci->getName()+".toascii",ci);
ci->replaceAllUsesWith(and_inst);
ci->eraseFromParent();
return true;
}
} ToAsciiOptimizer;
/// This LibCallOptimization will simplify calls to the "ffs" library
/// calls which find the first set bit in an int, long, or long long. The
/// optimization is to compute the result at compile time if the argument is
/// a constant.
/// @brief Simplify the ffs library function.
struct FFSOptimization : public LibCallOptimization
{
protected:
/// @brief Subclass Constructor
FFSOptimization(const char* funcName, const char* description)
: LibCallOptimization(funcName, description)
{}
public:
/// @brief Default Constructor
FFSOptimization() : LibCallOptimization("ffs",
"Number of 'ffs' calls simplified") {}
/// @brief Make sure that the "fputs" function has the right prototype
virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& SLC)
{
// Just make sure this has 2 arguments
return (f->arg_size() == 1 && f->getReturnType() == Type::IntTy);
}
/// @brief Perform the ffs optimization.
virtual bool OptimizeCall(CallInst* ci, SimplifyLibCalls& SLC)
{
if (ConstantInt* CI = dyn_cast<ConstantInt>(ci->getOperand(1)))
{
// ffs(cnst) -> bit#
// ffsl(cnst) -> bit#
// ffsll(cnst) -> bit#
uint64_t val = CI->getRawValue();
int result = 0;
while (val != 0) {
result +=1;
if (val&1)
break;
val >>= 1;
}
ci->replaceAllUsesWith(ConstantSInt::get(Type::IntTy, result));
ci->eraseFromParent();
return true;
}
// ffs(x) -> ( x == 0 ? 0 : llvm.cttz(x)+1)
// ffsl(x) -> ( x == 0 ? 0 : llvm.cttz(x)+1)
// ffsll(x) -> ( x == 0 ? 0 : llvm.cttz(x)+1)
const Type* arg_type = ci->getOperand(1)->getType();
std::vector<const Type*> args;
args.push_back(arg_type);
FunctionType* llvm_cttz_type = FunctionType::get(arg_type,args,false);
Function* F =
SLC.getModule()->getOrInsertFunction("llvm.cttz",llvm_cttz_type);
std::string inst_name(ci->getName()+".ffs");
Instruction* call =
new CallInst(F, ci->getOperand(1), inst_name, ci);
if (arg_type != Type::IntTy)
call = new CastInst(call, Type::IntTy, inst_name, ci);
BinaryOperator* add = BinaryOperator::createAdd(call,
ConstantSInt::get(Type::IntTy,1), inst_name, ci);
SetCondInst* eq = new SetCondInst(Instruction::SetEQ,ci->getOperand(1),
ConstantSInt::get(ci->getOperand(1)->getType(),0),inst_name,ci);
SelectInst* select = new SelectInst(eq,ConstantSInt::get(Type::IntTy,0),add,
inst_name,ci);
ci->replaceAllUsesWith(select);
ci->eraseFromParent();
return true;
}
} FFSOptimizer;
/// This LibCallOptimization will simplify calls to the "ffsl" library
/// calls. It simply uses FFSOptimization for which the transformation is
/// identical.
/// @brief Simplify the ffsl library function.
struct FFSLOptimization : public FFSOptimization
{
public:
/// @brief Default Constructor
FFSLOptimization() : FFSOptimization("ffsl",
"Number of 'ffsl' calls simplified") {}
} FFSLOptimizer;
/// This LibCallOptimization will simplify calls to the "ffsll" library
/// calls. It simply uses FFSOptimization for which the transformation is
/// identical.
/// @brief Simplify the ffsl library function.
struct FFSLLOptimization : public FFSOptimization
{
public:
/// @brief Default Constructor
FFSLLOptimization() : FFSOptimization("ffsll",
"Number of 'ffsll' calls simplified") {}
} FFSLLOptimizer;
/// This LibCallOptimization will simplify calls to the "floor" library
/// function.
/// @brief Simplify the floor library function.
struct FloorOptimization : public LibCallOptimization {
FloorOptimization()
: LibCallOptimization("floor", "Number of 'floor' calls simplified") {}
/// @brief Make sure that the "floor" function has the right prototype
virtual bool ValidateCalledFunction(const Function *F, SimplifyLibCalls &SLC){
return F->arg_size() == 1 && F->arg_begin()->getType() == Type::DoubleTy &&
F->getReturnType() == Type::DoubleTy;
}
virtual bool OptimizeCall(CallInst *CI, SimplifyLibCalls &SLC) {
// If this is a float argument passed in, convert to floorf.
// e.g. floor((double)FLT) -> (double)floorf(FLT). There can be no loss of
// precision due to this.
if (CastInst *Cast = dyn_cast<CastInst>(CI->getOperand(1)))
if (Cast->getOperand(0)->getType() == Type::FloatTy) {
Value *New = new CallInst(SLC.get_floorf(), Cast->getOperand(0),
CI->getName(), CI);
New = new CastInst(New, Type::DoubleTy, CI->getName(), CI);
CI->replaceAllUsesWith(New);
CI->eraseFromParent();
if (Cast->use_empty())
Cast->eraseFromParent();
return true;
}
return false; // opt failed
}
} FloorOptimizer;
/// A function to compute the length of a null-terminated constant array of
/// integers. This function can't rely on the size of the constant array
/// because there could be a null terminator in the middle of the array.
/// We also have to bail out if we find a non-integer constant initializer
/// of one of the elements or if there is no null-terminator. The logic
/// below checks each of these conditions and will return true only if all
/// conditions are met. In that case, the \p len parameter is set to the length
/// of the null-terminated string. If false is returned, the conditions were
/// not met and len is set to 0.
/// @brief Get the length of a constant string (null-terminated array).
bool getConstantStringLength(Value* V, uint64_t& len, ConstantArray** CA )
{
assert(V != 0 && "Invalid args to getConstantStringLength");
len = 0; // make sure we initialize this
User* GEP = 0;
// If the value is not a GEP instruction nor a constant expression with a
// GEP instruction, then return false because ConstantArray can't occur
// any other way
if (GetElementPtrInst* GEPI = dyn_cast<GetElementPtrInst>(V))
GEP = GEPI;
else if (ConstantExpr* CE = dyn_cast<ConstantExpr>(V))
if (CE->getOpcode() == Instruction::GetElementPtr)
GEP = CE;
else
return false;
else
return false;
// Make sure the GEP has exactly three arguments.
if (GEP->getNumOperands() != 3)
return false;
// Check to make sure that the first operand of the GEP is an integer and
// has value 0 so that we are sure we're indexing into the initializer.
if (ConstantInt* op1 = dyn_cast<ConstantInt>(GEP->getOperand(1)))
{
if (!op1->isNullValue())
return false;
}
else
return false;
// Ensure that the second operand is a ConstantInt. If it isn't then this
// GEP is wonky and we're not really sure what were referencing into and
// better of not optimizing it. While we're at it, get the second index
// value. We'll need this later for indexing the ConstantArray.
uint64_t start_idx = 0;
if (ConstantInt* CI = dyn_cast<ConstantInt>(GEP->getOperand(2)))
start_idx = CI->getRawValue();
else
return false;
// The GEP instruction, constant or instruction, must reference a global
// variable that is a constant and is initialized. The referenced constant
// initializer is the array that we'll use for optimization.
GlobalVariable* GV = dyn_cast<GlobalVariable>(GEP->getOperand(0));
if (!GV || !GV->isConstant() || !GV->hasInitializer())
return false;
// Get the initializer.
Constant* INTLZR = GV->getInitializer();
// Handle the ConstantAggregateZero case
if (ConstantAggregateZero* CAZ = dyn_cast<ConstantAggregateZero>(INTLZR))
{
// This is a degenerate case. The initializer is constant zero so the
// length of the string must be zero.
len = 0;
return true;
}
// Must be a Constant Array
ConstantArray* A = dyn_cast<ConstantArray>(INTLZR);
if (!A)
return false;
// Get the number of elements in the array
uint64_t max_elems = A->getType()->getNumElements();
// Traverse the constant array from start_idx (derived above) which is
// the place the GEP refers to in the array.
for ( len = start_idx; len < max_elems; len++)
{
if (ConstantInt* CI = dyn_cast<ConstantInt>(A->getOperand(len)))
{
// Check for the null terminator
if (CI->isNullValue())
break; // we found end of string
}
else
return false; // This array isn't suitable, non-int initializer
}
if (len >= max_elems)
return false; // This array isn't null terminated
// Subtract out the initial value from the length
len -= start_idx;
if (CA)
*CA = A;
return true; // success!
}
/// CastToCStr - Return V if it is an sbyte*, otherwise cast it to sbyte*,
/// inserting the cast before IP, and return the cast.
/// @brief Cast a value to a "C" string.
Value *CastToCStr(Value *V, Instruction &IP) {
const Type *SBPTy = PointerType::get(Type::SByteTy);
if (V->getType() != SBPTy)
return new CastInst(V, SBPTy, V->getName(), &IP);
return V;
}
// TODO:
// Additional cases that we need to add to this file:
//
// cbrt:
// * cbrt(expN(X)) -> expN(x/3)
// * cbrt(sqrt(x)) -> pow(x,1/6)
// * cbrt(sqrt(x)) -> pow(x,1/9)
//
// cos, cosf, cosl:
// * cos(-x) -> cos(x)
//
// exp, expf, expl:
// * exp(log(x)) -> x
//
// log, logf, logl:
// * log(exp(x)) -> x
// * log(x**y) -> y*log(x)
// * log(exp(y)) -> y*log(e)
// * log(exp2(y)) -> y*log(2)
// * log(exp10(y)) -> y*log(10)
// * log(sqrt(x)) -> 0.5*log(x)
// * log(pow(x,y)) -> y*log(x)
//
// lround, lroundf, lroundl:
// * lround(cnst) -> cnst'
//
// memcmp:
// * memcmp(x,y,l) -> cnst
// (if all arguments are constant and strlen(x) <= l and strlen(y) <= l)
//
// memmove:
// * memmove(d,s,l,a) -> memcpy(d,s,l,a)
// (if s is a global constant array)
//
// pow, powf, powl:
// * pow(exp(x),y) -> exp(x*y)
// * pow(sqrt(x),y) -> pow(x,y*0.5)
// * pow(pow(x,y),z)-> pow(x,y*z)
//
// puts:
// * puts("") -> fputc("\n",stdout) (how do we get "stdout"?)
//
// round, roundf, roundl:
// * round(cnst) -> cnst'
//
// signbit:
// * signbit(cnst) -> cnst'
// * signbit(nncst) -> 0 (if pstv is a non-negative constant)
//
// sqrt, sqrtf, sqrtl:
// * sqrt(expN(x)) -> expN(x*0.5)
// * sqrt(Nroot(x)) -> pow(x,1/(2*N))
// * sqrt(pow(x,y)) -> pow(|x|,y*0.5)
//
// stpcpy:
// * stpcpy(str, "literal") ->
// llvm.memcpy(str,"literal",strlen("literal")+1,1)
// strrchr:
// * strrchr(s,c) -> reverse_offset_of_in(c,s)
// (if c is a constant integer and s is a constant string)
// * strrchr(s1,0) -> strchr(s1,0)
//
// strncat:
// * strncat(x,y,0) -> x
// * strncat(x,y,0) -> x (if strlen(y) = 0)
// * strncat(x,y,l) -> strcat(x,y) (if y and l are constants an l > strlen(y))
//
// strncpy:
// * strncpy(d,s,0) -> d
// * strncpy(d,s,l) -> memcpy(d,s,l,1)
// (if s and l are constants)
//
// strpbrk:
// * strpbrk(s,a) -> offset_in_for(s,a)
// (if s and a are both constant strings)
// * strpbrk(s,"") -> 0
// * strpbrk(s,a) -> strchr(s,a[0]) (if a is constant string of length 1)
//
// strspn, strcspn:
// * strspn(s,a) -> const_int (if both args are constant)
// * strspn("",a) -> 0
// * strspn(s,"") -> 0
// * strcspn(s,a) -> const_int (if both args are constant)
// * strcspn("",a) -> 0
// * strcspn(s,"") -> strlen(a)
//
// strstr:
// * strstr(x,x) -> x
// * strstr(s1,s2) -> offset_of_s2_in(s1)
// (if s1 and s2 are constant strings)
//
// tan, tanf, tanl:
// * tan(atan(x)) -> x
//
// trunc, truncf, truncl:
// * trunc(cnst) -> cnst'
//
//
}
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