llvm-6502/lib/Transforms/IPO/IPConstantPropagation.cpp
Reid Spencer 9133fe2895 Apply the VISIBILITY_HIDDEN field to the remaining anonymous classes in
the Transforms library. This reduces debug library size by 132 KB, debug
binary size by 376 KB, and reduces link time for llvm tools slightly.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@33939 91177308-0d34-0410-b5e6-96231b3b80d8
2007-02-05 23:32:05 +00:00

194 lines
7.0 KiB
C++

//===-- IPConstantPropagation.cpp - Propagate constants through calls -----===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass implements an _extremely_ simple interprocedural constant
// propagation pass. It could certainly be improved in many different ways,
// like using a worklist. This pass makes arguments dead, but does not remove
// them. The existing dead argument elimination pass should be run after this
// to clean up the mess.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "ipconstprop"
#include "llvm/Transforms/IPO.h"
#include "llvm/Constants.h"
#include "llvm/Instructions.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/Support/CallSite.h"
#include "llvm/Support/Compiler.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;
STATISTIC(NumArgumentsProped, "Number of args turned into constants");
STATISTIC(NumReturnValProped, "Number of return values turned into constants");
namespace {
/// IPCP - The interprocedural constant propagation pass
///
struct VISIBILITY_HIDDEN IPCP : public ModulePass {
bool runOnModule(Module &M);
private:
bool PropagateConstantsIntoArguments(Function &F);
bool PropagateConstantReturn(Function &F);
};
RegisterPass<IPCP> X("ipconstprop", "Interprocedural constant propagation");
}
ModulePass *llvm::createIPConstantPropagationPass() { return new IPCP(); }
bool IPCP::runOnModule(Module &M) {
bool Changed = false;
bool LocalChange = true;
// FIXME: instead of using smart algorithms, we just iterate until we stop
// making changes.
while (LocalChange) {
LocalChange = false;
for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
if (!I->isDeclaration()) {
// Delete any klingons.
I->removeDeadConstantUsers();
if (I->hasInternalLinkage())
LocalChange |= PropagateConstantsIntoArguments(*I);
Changed |= PropagateConstantReturn(*I);
}
Changed |= LocalChange;
}
return Changed;
}
/// PropagateConstantsIntoArguments - Look at all uses of the specified
/// function. If all uses are direct call sites, and all pass a particular
/// constant in for an argument, propagate that constant in as the argument.
///
bool IPCP::PropagateConstantsIntoArguments(Function &F) {
if (F.arg_empty() || F.use_empty()) return false; // No arguments? Early exit.
std::vector<std::pair<Constant*, bool> > ArgumentConstants;
ArgumentConstants.resize(F.arg_size());
unsigned NumNonconstant = 0;
for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I)
if (!isa<Instruction>(*I))
return false; // Used by a non-instruction, do not transform
else {
CallSite CS = CallSite::get(cast<Instruction>(*I));
if (CS.getInstruction() == 0 ||
CS.getCalledFunction() != &F)
return false; // Not a direct call site?
// Check out all of the potentially constant arguments
CallSite::arg_iterator AI = CS.arg_begin();
Function::arg_iterator Arg = F.arg_begin();
for (unsigned i = 0, e = ArgumentConstants.size(); i != e;
++i, ++AI, ++Arg) {
if (*AI == &F) return false; // Passes the function into itself
if (!ArgumentConstants[i].second) {
if (Constant *C = dyn_cast<Constant>(*AI)) {
if (!ArgumentConstants[i].first)
ArgumentConstants[i].first = C;
else if (ArgumentConstants[i].first != C) {
// Became non-constant
ArgumentConstants[i].second = true;
++NumNonconstant;
if (NumNonconstant == ArgumentConstants.size()) return false;
}
} else if (*AI != &*Arg) { // Ignore recursive calls with same arg
// This is not a constant argument. Mark the argument as
// non-constant.
ArgumentConstants[i].second = true;
++NumNonconstant;
if (NumNonconstant == ArgumentConstants.size()) return false;
}
}
}
}
// If we got to this point, there is a constant argument!
assert(NumNonconstant != ArgumentConstants.size());
Function::arg_iterator AI = F.arg_begin();
bool MadeChange = false;
for (unsigned i = 0, e = ArgumentConstants.size(); i != e; ++i, ++AI)
// Do we have a constant argument!?
if (!ArgumentConstants[i].second && !AI->use_empty()) {
Value *V = ArgumentConstants[i].first;
if (V == 0) V = UndefValue::get(AI->getType());
AI->replaceAllUsesWith(V);
++NumArgumentsProped;
MadeChange = true;
}
return MadeChange;
}
// Check to see if this function returns a constant. If so, replace all callers
// that user the return value with the returned valued. If we can replace ALL
// callers,
bool IPCP::PropagateConstantReturn(Function &F) {
if (F.getReturnType() == Type::VoidTy)
return false; // No return value.
// Check to see if this function returns a constant.
Value *RetVal = 0;
for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
if (isa<UndefValue>(RI->getOperand(0))) {
// Ignore.
} else if (Constant *C = dyn_cast<Constant>(RI->getOperand(0))) {
if (RetVal == 0)
RetVal = C;
else if (RetVal != C)
return false; // Does not return the same constant.
} else {
return false; // Does not return a constant.
}
if (RetVal == 0) RetVal = UndefValue::get(F.getReturnType());
// If we got here, the function returns a constant value. Loop over all
// users, replacing any uses of the return value with the returned constant.
bool ReplacedAllUsers = true;
bool MadeChange = false;
for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I)
if (!isa<Instruction>(*I))
ReplacedAllUsers = false;
else {
CallSite CS = CallSite::get(cast<Instruction>(*I));
if (CS.getInstruction() == 0 ||
CS.getCalledFunction() != &F) {
ReplacedAllUsers = false;
} else {
if (!CS.getInstruction()->use_empty()) {
CS.getInstruction()->replaceAllUsesWith(RetVal);
MadeChange = true;
}
}
}
// If we replace all users with the returned constant, and there can be no
// other callers of the function, replace the constant being returned in the
// function with an undef value.
if (ReplacedAllUsers && F.hasInternalLinkage() && !isa<UndefValue>(RetVal)) {
Value *RV = UndefValue::get(RetVal->getType());
for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
if (RI->getOperand(0) != RV) {
RI->setOperand(0, RV);
MadeChange = true;
}
}
}
if (MadeChange) ++NumReturnValProped;
return MadeChange;
}