llvm-6502/lib/Analysis/InlineCost.cpp
Chandler Carruth 426c2bf5cd Revert the majority of the next patch in the address space series:
r165941: Resubmit the changes to llvm core to update the functions to
         support different pointer sizes on a per address space basis.

Despite this commit log, this change primarily changed stuff outside of
VMCore, and those changes do not carry any tests for correctness (or
even plausibility), and we have consistently found questionable or flat
out incorrect cases in these changes. Most of them are probably correct,
but we need to devise a system that makes it more clear when we have
handled the address space concerns correctly, and ideally each pass that
gets updated would receive an accompanying test case that exercises that
pass specificaly w.r.t. alternate address spaces.

However, from this commit, I have retained the new C API entry points.
Those were an orthogonal change that probably should have been split
apart, but they seem entirely good.

In several places the changes were very obvious cleanups with no actual
multiple address space code added; these I have not reverted when
I spotted them.

In a few other places there were merge conflicts due to a cleaner
solution being implemented later, often not using address spaces at all.
In those cases, I've preserved the new code which isn't address space
dependent.

This is part of my ongoing effort to clean out the partial address space
code which carries high risk and low test coverage, and not likely to be
finished before the 3.2 release looms closer. Duncan and I would both
like to see the above issues addressed before we return to these
changes.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@167222 91177308-0d34-0410-b5e6-96231b3b80d8
2012-11-01 09:14:31 +00:00

1068 lines
39 KiB
C++

//===- InlineCost.cpp - Cost analysis for inliner -------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements inline cost analysis.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "inline-cost"
#include "llvm/Analysis/InlineCost.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Support/CallSite.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/InstVisitor.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/CallingConv.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Operator.h"
#include "llvm/GlobalAlias.h"
#include "llvm/DataLayout.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;
STATISTIC(NumCallsAnalyzed, "Number of call sites analyzed");
namespace {
class CallAnalyzer : public InstVisitor<CallAnalyzer, bool> {
typedef InstVisitor<CallAnalyzer, bool> Base;
friend class InstVisitor<CallAnalyzer, bool>;
// DataLayout if available, or null.
const DataLayout *const TD;
// The called function.
Function &F;
int Threshold;
int Cost;
const bool AlwaysInline;
bool IsCallerRecursive;
bool IsRecursiveCall;
bool ExposesReturnsTwice;
bool HasDynamicAlloca;
/// Number of bytes allocated statically by the callee.
uint64_t AllocatedSize;
unsigned NumInstructions, NumVectorInstructions;
int FiftyPercentVectorBonus, TenPercentVectorBonus;
int VectorBonus;
// While we walk the potentially-inlined instructions, we build up and
// maintain a mapping of simplified values specific to this callsite. The
// idea is to propagate any special information we have about arguments to
// this call through the inlinable section of the function, and account for
// likely simplifications post-inlining. The most important aspect we track
// is CFG altering simplifications -- when we prove a basic block dead, that
// can cause dramatic shifts in the cost of inlining a function.
DenseMap<Value *, Constant *> SimplifiedValues;
// Keep track of the values which map back (through function arguments) to
// allocas on the caller stack which could be simplified through SROA.
DenseMap<Value *, Value *> SROAArgValues;
// The mapping of caller Alloca values to their accumulated cost savings. If
// we have to disable SROA for one of the allocas, this tells us how much
// cost must be added.
DenseMap<Value *, int> SROAArgCosts;
// Keep track of values which map to a pointer base and constant offset.
DenseMap<Value *, std::pair<Value *, APInt> > ConstantOffsetPtrs;
// Custom simplification helper routines.
bool isAllocaDerivedArg(Value *V);
bool lookupSROAArgAndCost(Value *V, Value *&Arg,
DenseMap<Value *, int>::iterator &CostIt);
void disableSROA(DenseMap<Value *, int>::iterator CostIt);
void disableSROA(Value *V);
void accumulateSROACost(DenseMap<Value *, int>::iterator CostIt,
int InstructionCost);
bool handleSROACandidate(bool IsSROAValid,
DenseMap<Value *, int>::iterator CostIt,
int InstructionCost);
bool isGEPOffsetConstant(GetElementPtrInst &GEP);
bool accumulateGEPOffset(GEPOperator &GEP, APInt &Offset);
ConstantInt *stripAndComputeInBoundsConstantOffsets(Value *&V);
// Custom analysis routines.
bool analyzeBlock(BasicBlock *BB);
// Disable several entry points to the visitor so we don't accidentally use
// them by declaring but not defining them here.
void visit(Module *); void visit(Module &);
void visit(Function *); void visit(Function &);
void visit(BasicBlock *); void visit(BasicBlock &);
// Provide base case for our instruction visit.
bool visitInstruction(Instruction &I);
// Our visit overrides.
bool visitAlloca(AllocaInst &I);
bool visitPHI(PHINode &I);
bool visitGetElementPtr(GetElementPtrInst &I);
bool visitBitCast(BitCastInst &I);
bool visitPtrToInt(PtrToIntInst &I);
bool visitIntToPtr(IntToPtrInst &I);
bool visitCastInst(CastInst &I);
bool visitUnaryInstruction(UnaryInstruction &I);
bool visitICmp(ICmpInst &I);
bool visitSub(BinaryOperator &I);
bool visitBinaryOperator(BinaryOperator &I);
bool visitLoad(LoadInst &I);
bool visitStore(StoreInst &I);
bool visitCallSite(CallSite CS);
public:
CallAnalyzer(const DataLayout *TD, Function &Callee, int Threshold)
: TD(TD), F(Callee), Threshold(Threshold), Cost(0),
AlwaysInline(F.getFnAttributes().hasAttribute(Attributes::AlwaysInline)),
IsCallerRecursive(false), IsRecursiveCall(false),
ExposesReturnsTwice(false), HasDynamicAlloca(false), AllocatedSize(0),
NumInstructions(0), NumVectorInstructions(0),
FiftyPercentVectorBonus(0), TenPercentVectorBonus(0), VectorBonus(0),
NumConstantArgs(0), NumConstantOffsetPtrArgs(0), NumAllocaArgs(0),
NumConstantPtrCmps(0), NumConstantPtrDiffs(0),
NumInstructionsSimplified(0), SROACostSavings(0), SROACostSavingsLost(0) {
}
bool analyzeCall(CallSite CS);
int getThreshold() { return Threshold; }
int getCost() { return Cost; }
bool isAlwaysInline() { return AlwaysInline; }
// Keep a bunch of stats about the cost savings found so we can print them
// out when debugging.
unsigned NumConstantArgs;
unsigned NumConstantOffsetPtrArgs;
unsigned NumAllocaArgs;
unsigned NumConstantPtrCmps;
unsigned NumConstantPtrDiffs;
unsigned NumInstructionsSimplified;
unsigned SROACostSavings;
unsigned SROACostSavingsLost;
void dump();
};
} // namespace
/// \brief Test whether the given value is an Alloca-derived function argument.
bool CallAnalyzer::isAllocaDerivedArg(Value *V) {
return SROAArgValues.count(V);
}
/// \brief Lookup the SROA-candidate argument and cost iterator which V maps to.
/// Returns false if V does not map to a SROA-candidate.
bool CallAnalyzer::lookupSROAArgAndCost(
Value *V, Value *&Arg, DenseMap<Value *, int>::iterator &CostIt) {
if (SROAArgValues.empty() || SROAArgCosts.empty())
return false;
DenseMap<Value *, Value *>::iterator ArgIt = SROAArgValues.find(V);
if (ArgIt == SROAArgValues.end())
return false;
Arg = ArgIt->second;
CostIt = SROAArgCosts.find(Arg);
return CostIt != SROAArgCosts.end();
}
/// \brief Disable SROA for the candidate marked by this cost iterator.
///
/// This marks the candidate as no longer viable for SROA, and adds the cost
/// savings associated with it back into the inline cost measurement.
void CallAnalyzer::disableSROA(DenseMap<Value *, int>::iterator CostIt) {
// If we're no longer able to perform SROA we need to undo its cost savings
// and prevent subsequent analysis.
Cost += CostIt->second;
SROACostSavings -= CostIt->second;
SROACostSavingsLost += CostIt->second;
SROAArgCosts.erase(CostIt);
}
/// \brief If 'V' maps to a SROA candidate, disable SROA for it.
void CallAnalyzer::disableSROA(Value *V) {
Value *SROAArg;
DenseMap<Value *, int>::iterator CostIt;
if (lookupSROAArgAndCost(V, SROAArg, CostIt))
disableSROA(CostIt);
}
/// \brief Accumulate the given cost for a particular SROA candidate.
void CallAnalyzer::accumulateSROACost(DenseMap<Value *, int>::iterator CostIt,
int InstructionCost) {
CostIt->second += InstructionCost;
SROACostSavings += InstructionCost;
}
/// \brief Helper for the common pattern of handling a SROA candidate.
/// Either accumulates the cost savings if the SROA remains valid, or disables
/// SROA for the candidate.
bool CallAnalyzer::handleSROACandidate(bool IsSROAValid,
DenseMap<Value *, int>::iterator CostIt,
int InstructionCost) {
if (IsSROAValid) {
accumulateSROACost(CostIt, InstructionCost);
return true;
}
disableSROA(CostIt);
return false;
}
/// \brief Check whether a GEP's indices are all constant.
///
/// Respects any simplified values known during the analysis of this callsite.
bool CallAnalyzer::isGEPOffsetConstant(GetElementPtrInst &GEP) {
for (User::op_iterator I = GEP.idx_begin(), E = GEP.idx_end(); I != E; ++I)
if (!isa<Constant>(*I) && !SimplifiedValues.lookup(*I))
return false;
return true;
}
/// \brief Accumulate a constant GEP offset into an APInt if possible.
///
/// Returns false if unable to compute the offset for any reason. Respects any
/// simplified values known during the analysis of this callsite.
bool CallAnalyzer::accumulateGEPOffset(GEPOperator &GEP, APInt &Offset) {
if (!TD)
return false;
unsigned IntPtrWidth = TD->getPointerSizeInBits();
assert(IntPtrWidth == Offset.getBitWidth());
for (gep_type_iterator GTI = gep_type_begin(GEP), GTE = gep_type_end(GEP);
GTI != GTE; ++GTI) {
ConstantInt *OpC = dyn_cast<ConstantInt>(GTI.getOperand());
if (!OpC)
if (Constant *SimpleOp = SimplifiedValues.lookup(GTI.getOperand()))
OpC = dyn_cast<ConstantInt>(SimpleOp);
if (!OpC)
return false;
if (OpC->isZero()) continue;
// Handle a struct index, which adds its field offset to the pointer.
if (StructType *STy = dyn_cast<StructType>(*GTI)) {
unsigned ElementIdx = OpC->getZExtValue();
const StructLayout *SL = TD->getStructLayout(STy);
Offset += APInt(IntPtrWidth, SL->getElementOffset(ElementIdx));
continue;
}
APInt TypeSize(IntPtrWidth, TD->getTypeAllocSize(GTI.getIndexedType()));
Offset += OpC->getValue().sextOrTrunc(IntPtrWidth) * TypeSize;
}
return true;
}
bool CallAnalyzer::visitAlloca(AllocaInst &I) {
// FIXME: Check whether inlining will turn a dynamic alloca into a static
// alloca, and handle that case.
// Accumulate the allocated size.
if (I.isStaticAlloca()) {
Type *Ty = I.getAllocatedType();
AllocatedSize += (TD ? TD->getTypeAllocSize(Ty) :
Ty->getPrimitiveSizeInBits());
}
// We will happily inline static alloca instructions or dynamic alloca
// instructions in always-inline situations.
if (AlwaysInline || I.isStaticAlloca())
return Base::visitAlloca(I);
// FIXME: This is overly conservative. Dynamic allocas are inefficient for
// a variety of reasons, and so we would like to not inline them into
// functions which don't currently have a dynamic alloca. This simply
// disables inlining altogether in the presence of a dynamic alloca.
HasDynamicAlloca = true;
return false;
}
bool CallAnalyzer::visitPHI(PHINode &I) {
// FIXME: We should potentially be tracking values through phi nodes,
// especially when they collapse to a single value due to deleted CFG edges
// during inlining.
// FIXME: We need to propagate SROA *disabling* through phi nodes, even
// though we don't want to propagate it's bonuses. The idea is to disable
// SROA if it *might* be used in an inappropriate manner.
// Phi nodes are always zero-cost.
return true;
}
bool CallAnalyzer::visitGetElementPtr(GetElementPtrInst &I) {
Value *SROAArg;
DenseMap<Value *, int>::iterator CostIt;
bool SROACandidate = lookupSROAArgAndCost(I.getPointerOperand(),
SROAArg, CostIt);
// Try to fold GEPs of constant-offset call site argument pointers. This
// requires target data and inbounds GEPs.
if (TD && I.isInBounds()) {
// Check if we have a base + offset for the pointer.
Value *Ptr = I.getPointerOperand();
std::pair<Value *, APInt> BaseAndOffset = ConstantOffsetPtrs.lookup(Ptr);
if (BaseAndOffset.first) {
// Check if the offset of this GEP is constant, and if so accumulate it
// into Offset.
if (!accumulateGEPOffset(cast<GEPOperator>(I), BaseAndOffset.second)) {
// Non-constant GEPs aren't folded, and disable SROA.
if (SROACandidate)
disableSROA(CostIt);
return false;
}
// Add the result as a new mapping to Base + Offset.
ConstantOffsetPtrs[&I] = BaseAndOffset;
// Also handle SROA candidates here, we already know that the GEP is
// all-constant indexed.
if (SROACandidate)
SROAArgValues[&I] = SROAArg;
return true;
}
}
if (isGEPOffsetConstant(I)) {
if (SROACandidate)
SROAArgValues[&I] = SROAArg;
// Constant GEPs are modeled as free.
return true;
}
// Variable GEPs will require math and will disable SROA.
if (SROACandidate)
disableSROA(CostIt);
return false;
}
bool CallAnalyzer::visitBitCast(BitCastInst &I) {
// Propagate constants through bitcasts.
if (Constant *COp = dyn_cast<Constant>(I.getOperand(0)))
if (Constant *C = ConstantExpr::getBitCast(COp, I.getType())) {
SimplifiedValues[&I] = C;
return true;
}
// Track base/offsets through casts
std::pair<Value *, APInt> BaseAndOffset
= ConstantOffsetPtrs.lookup(I.getOperand(0));
// Casts don't change the offset, just wrap it up.
if (BaseAndOffset.first)
ConstantOffsetPtrs[&I] = BaseAndOffset;
// Also look for SROA candidates here.
Value *SROAArg;
DenseMap<Value *, int>::iterator CostIt;
if (lookupSROAArgAndCost(I.getOperand(0), SROAArg, CostIt))
SROAArgValues[&I] = SROAArg;
// Bitcasts are always zero cost.
return true;
}
bool CallAnalyzer::visitPtrToInt(PtrToIntInst &I) {
// Propagate constants through ptrtoint.
if (Constant *COp = dyn_cast<Constant>(I.getOperand(0)))
if (Constant *C = ConstantExpr::getPtrToInt(COp, I.getType())) {
SimplifiedValues[&I] = C;
return true;
}
// Track base/offset pairs when converted to a plain integer provided the
// integer is large enough to represent the pointer.
unsigned IntegerSize = I.getType()->getScalarSizeInBits();
if (TD && IntegerSize >= TD->getPointerSizeInBits()) {
std::pair<Value *, APInt> BaseAndOffset
= ConstantOffsetPtrs.lookup(I.getOperand(0));
if (BaseAndOffset.first)
ConstantOffsetPtrs[&I] = BaseAndOffset;
}
// This is really weird. Technically, ptrtoint will disable SROA. However,
// unless that ptrtoint is *used* somewhere in the live basic blocks after
// inlining, it will be nuked, and SROA should proceed. All of the uses which
// would block SROA would also block SROA if applied directly to a pointer,
// and so we can just add the integer in here. The only places where SROA is
// preserved either cannot fire on an integer, or won't in-and-of themselves
// disable SROA (ext) w/o some later use that we would see and disable.
Value *SROAArg;
DenseMap<Value *, int>::iterator CostIt;
if (lookupSROAArgAndCost(I.getOperand(0), SROAArg, CostIt))
SROAArgValues[&I] = SROAArg;
return isInstructionFree(&I, TD);
}
bool CallAnalyzer::visitIntToPtr(IntToPtrInst &I) {
// Propagate constants through ptrtoint.
if (Constant *COp = dyn_cast<Constant>(I.getOperand(0)))
if (Constant *C = ConstantExpr::getIntToPtr(COp, I.getType())) {
SimplifiedValues[&I] = C;
return true;
}
// Track base/offset pairs when round-tripped through a pointer without
// modifications provided the integer is not too large.
Value *Op = I.getOperand(0);
unsigned IntegerSize = Op->getType()->getScalarSizeInBits();
if (TD && IntegerSize <= TD->getPointerSizeInBits()) {
std::pair<Value *, APInt> BaseAndOffset = ConstantOffsetPtrs.lookup(Op);
if (BaseAndOffset.first)
ConstantOffsetPtrs[&I] = BaseAndOffset;
}
// "Propagate" SROA here in the same manner as we do for ptrtoint above.
Value *SROAArg;
DenseMap<Value *, int>::iterator CostIt;
if (lookupSROAArgAndCost(Op, SROAArg, CostIt))
SROAArgValues[&I] = SROAArg;
return isInstructionFree(&I, TD);
}
bool CallAnalyzer::visitCastInst(CastInst &I) {
// Propagate constants through ptrtoint.
if (Constant *COp = dyn_cast<Constant>(I.getOperand(0)))
if (Constant *C = ConstantExpr::getCast(I.getOpcode(), COp, I.getType())) {
SimplifiedValues[&I] = C;
return true;
}
// Disable SROA in the face of arbitrary casts we don't whitelist elsewhere.
disableSROA(I.getOperand(0));
return isInstructionFree(&I, TD);
}
bool CallAnalyzer::visitUnaryInstruction(UnaryInstruction &I) {
Value *Operand = I.getOperand(0);
Constant *Ops[1] = { dyn_cast<Constant>(Operand) };
if (Ops[0] || (Ops[0] = SimplifiedValues.lookup(Operand)))
if (Constant *C = ConstantFoldInstOperands(I.getOpcode(), I.getType(),
Ops, TD)) {
SimplifiedValues[&I] = C;
return true;
}
// Disable any SROA on the argument to arbitrary unary operators.
disableSROA(Operand);
return false;
}
bool CallAnalyzer::visitICmp(ICmpInst &I) {
Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
// First try to handle simplified comparisons.
if (!isa<Constant>(LHS))
if (Constant *SimpleLHS = SimplifiedValues.lookup(LHS))
LHS = SimpleLHS;
if (!isa<Constant>(RHS))
if (Constant *SimpleRHS = SimplifiedValues.lookup(RHS))
RHS = SimpleRHS;
if (Constant *CLHS = dyn_cast<Constant>(LHS))
if (Constant *CRHS = dyn_cast<Constant>(RHS))
if (Constant *C = ConstantExpr::getICmp(I.getPredicate(), CLHS, CRHS)) {
SimplifiedValues[&I] = C;
return true;
}
// Otherwise look for a comparison between constant offset pointers with
// a common base.
Value *LHSBase, *RHSBase;
APInt LHSOffset, RHSOffset;
llvm::tie(LHSBase, LHSOffset) = ConstantOffsetPtrs.lookup(LHS);
if (LHSBase) {
llvm::tie(RHSBase, RHSOffset) = ConstantOffsetPtrs.lookup(RHS);
if (RHSBase && LHSBase == RHSBase) {
// We have common bases, fold the icmp to a constant based on the
// offsets.
Constant *CLHS = ConstantInt::get(LHS->getContext(), LHSOffset);
Constant *CRHS = ConstantInt::get(RHS->getContext(), RHSOffset);
if (Constant *C = ConstantExpr::getICmp(I.getPredicate(), CLHS, CRHS)) {
SimplifiedValues[&I] = C;
++NumConstantPtrCmps;
return true;
}
}
}
// If the comparison is an equality comparison with null, we can simplify it
// for any alloca-derived argument.
if (I.isEquality() && isa<ConstantPointerNull>(I.getOperand(1)))
if (isAllocaDerivedArg(I.getOperand(0))) {
// We can actually predict the result of comparisons between an
// alloca-derived value and null. Note that this fires regardless of
// SROA firing.
bool IsNotEqual = I.getPredicate() == CmpInst::ICMP_NE;
SimplifiedValues[&I] = IsNotEqual ? ConstantInt::getTrue(I.getType())
: ConstantInt::getFalse(I.getType());
return true;
}
// Finally check for SROA candidates in comparisons.
Value *SROAArg;
DenseMap<Value *, int>::iterator CostIt;
if (lookupSROAArgAndCost(I.getOperand(0), SROAArg, CostIt)) {
if (isa<ConstantPointerNull>(I.getOperand(1))) {
accumulateSROACost(CostIt, InlineConstants::InstrCost);
return true;
}
disableSROA(CostIt);
}
return false;
}
bool CallAnalyzer::visitSub(BinaryOperator &I) {
// Try to handle a special case: we can fold computing the difference of two
// constant-related pointers.
Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
Value *LHSBase, *RHSBase;
APInt LHSOffset, RHSOffset;
llvm::tie(LHSBase, LHSOffset) = ConstantOffsetPtrs.lookup(LHS);
if (LHSBase) {
llvm::tie(RHSBase, RHSOffset) = ConstantOffsetPtrs.lookup(RHS);
if (RHSBase && LHSBase == RHSBase) {
// We have common bases, fold the subtract to a constant based on the
// offsets.
Constant *CLHS = ConstantInt::get(LHS->getContext(), LHSOffset);
Constant *CRHS = ConstantInt::get(RHS->getContext(), RHSOffset);
if (Constant *C = ConstantExpr::getSub(CLHS, CRHS)) {
SimplifiedValues[&I] = C;
++NumConstantPtrDiffs;
return true;
}
}
}
// Otherwise, fall back to the generic logic for simplifying and handling
// instructions.
return Base::visitSub(I);
}
bool CallAnalyzer::visitBinaryOperator(BinaryOperator &I) {
Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
if (!isa<Constant>(LHS))
if (Constant *SimpleLHS = SimplifiedValues.lookup(LHS))
LHS = SimpleLHS;
if (!isa<Constant>(RHS))
if (Constant *SimpleRHS = SimplifiedValues.lookup(RHS))
RHS = SimpleRHS;
Value *SimpleV = SimplifyBinOp(I.getOpcode(), LHS, RHS, TD);
if (Constant *C = dyn_cast_or_null<Constant>(SimpleV)) {
SimplifiedValues[&I] = C;
return true;
}
// Disable any SROA on arguments to arbitrary, unsimplified binary operators.
disableSROA(LHS);
disableSROA(RHS);
return false;
}
bool CallAnalyzer::visitLoad(LoadInst &I) {
Value *SROAArg;
DenseMap<Value *, int>::iterator CostIt;
if (lookupSROAArgAndCost(I.getOperand(0), SROAArg, CostIt)) {
if (I.isSimple()) {
accumulateSROACost(CostIt, InlineConstants::InstrCost);
return true;
}
disableSROA(CostIt);
}
return false;
}
bool CallAnalyzer::visitStore(StoreInst &I) {
Value *SROAArg;
DenseMap<Value *, int>::iterator CostIt;
if (lookupSROAArgAndCost(I.getOperand(0), SROAArg, CostIt)) {
if (I.isSimple()) {
accumulateSROACost(CostIt, InlineConstants::InstrCost);
return true;
}
disableSROA(CostIt);
}
return false;
}
bool CallAnalyzer::visitCallSite(CallSite CS) {
if (CS.isCall() && cast<CallInst>(CS.getInstruction())->canReturnTwice() &&
!F.getFnAttributes().hasAttribute(Attributes::ReturnsTwice)) {
// This aborts the entire analysis.
ExposesReturnsTwice = true;
return false;
}
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction())) {
switch (II->getIntrinsicID()) {
default:
return Base::visitCallSite(CS);
case Intrinsic::memset:
case Intrinsic::memcpy:
case Intrinsic::memmove:
// SROA can usually chew through these intrinsics, but they aren't free.
return false;
}
}
if (Function *F = CS.getCalledFunction()) {
if (F == CS.getInstruction()->getParent()->getParent()) {
// This flag will fully abort the analysis, so don't bother with anything
// else.
IsRecursiveCall = true;
return false;
}
if (!callIsSmall(CS)) {
// We account for the average 1 instruction per call argument setup
// here.
Cost += CS.arg_size() * InlineConstants::InstrCost;
// Everything other than inline ASM will also have a significant cost
// merely from making the call.
if (!isa<InlineAsm>(CS.getCalledValue()))
Cost += InlineConstants::CallPenalty;
}
return Base::visitCallSite(CS);
}
// Otherwise we're in a very special case -- an indirect function call. See
// if we can be particularly clever about this.
Value *Callee = CS.getCalledValue();
// First, pay the price of the argument setup. We account for the average
// 1 instruction per call argument setup here.
Cost += CS.arg_size() * InlineConstants::InstrCost;
// Next, check if this happens to be an indirect function call to a known
// function in this inline context. If not, we've done all we can.
Function *F = dyn_cast_or_null<Function>(SimplifiedValues.lookup(Callee));
if (!F)
return Base::visitCallSite(CS);
// If we have a constant that we are calling as a function, we can peer
// through it and see the function target. This happens not infrequently
// during devirtualization and so we want to give it a hefty bonus for
// inlining, but cap that bonus in the event that inlining wouldn't pan
// out. Pretend to inline the function, with a custom threshold.
CallAnalyzer CA(TD, *F, InlineConstants::IndirectCallThreshold);
if (CA.analyzeCall(CS)) {
// We were able to inline the indirect call! Subtract the cost from the
// bonus we want to apply, but don't go below zero.
Cost -= std::max(0, InlineConstants::IndirectCallThreshold - CA.getCost());
}
return Base::visitCallSite(CS);
}
bool CallAnalyzer::visitInstruction(Instruction &I) {
// Some instructions are free. All of the free intrinsics can also be
// handled by SROA, etc.
if (isInstructionFree(&I, TD))
return true;
// We found something we don't understand or can't handle. Mark any SROA-able
// values in the operand list as no longer viable.
for (User::op_iterator OI = I.op_begin(), OE = I.op_end(); OI != OE; ++OI)
disableSROA(*OI);
return false;
}
/// \brief Analyze a basic block for its contribution to the inline cost.
///
/// This method walks the analyzer over every instruction in the given basic
/// block and accounts for their cost during inlining at this callsite. It
/// aborts early if the threshold has been exceeded or an impossible to inline
/// construct has been detected. It returns false if inlining is no longer
/// viable, and true if inlining remains viable.
bool CallAnalyzer::analyzeBlock(BasicBlock *BB) {
for (BasicBlock::iterator I = BB->begin(), E = llvm::prior(BB->end());
I != E; ++I) {
++NumInstructions;
if (isa<ExtractElementInst>(I) || I->getType()->isVectorTy())
++NumVectorInstructions;
// If the instruction simplified to a constant, there is no cost to this
// instruction. Visit the instructions using our InstVisitor to account for
// all of the per-instruction logic. The visit tree returns true if we
// consumed the instruction in any way, and false if the instruction's base
// cost should count against inlining.
if (Base::visit(I))
++NumInstructionsSimplified;
else
Cost += InlineConstants::InstrCost;
// If the visit this instruction detected an uninlinable pattern, abort.
if (IsRecursiveCall || ExposesReturnsTwice || HasDynamicAlloca)
return false;
// If the caller is a recursive function then we don't want to inline
// functions which allocate a lot of stack space because it would increase
// the caller stack usage dramatically.
if (IsCallerRecursive &&
AllocatedSize > InlineConstants::TotalAllocaSizeRecursiveCaller)
return false;
if (NumVectorInstructions > NumInstructions/2)
VectorBonus = FiftyPercentVectorBonus;
else if (NumVectorInstructions > NumInstructions/10)
VectorBonus = TenPercentVectorBonus;
else
VectorBonus = 0;
// Check if we've past the threshold so we don't spin in huge basic
// blocks that will never inline.
if (!AlwaysInline && Cost > (Threshold + VectorBonus))
return false;
}
return true;
}
/// \brief Compute the base pointer and cumulative constant offsets for V.
///
/// This strips all constant offsets off of V, leaving it the base pointer, and
/// accumulates the total constant offset applied in the returned constant. It
/// returns 0 if V is not a pointer, and returns the constant '0' if there are
/// no constant offsets applied.
ConstantInt *CallAnalyzer::stripAndComputeInBoundsConstantOffsets(Value *&V) {
if (!TD || !V->getType()->isPointerTy())
return 0;
unsigned IntPtrWidth = TD->getPointerSizeInBits();
APInt Offset = APInt::getNullValue(IntPtrWidth);
// Even though we don't look through PHI nodes, we could be called on an
// instruction in an unreachable block, which may be on a cycle.
SmallPtrSet<Value *, 4> Visited;
Visited.insert(V);
do {
if (GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
if (!GEP->isInBounds() || !accumulateGEPOffset(*GEP, Offset))
return 0;
V = GEP->getPointerOperand();
} else if (Operator::getOpcode(V) == Instruction::BitCast) {
V = cast<Operator>(V)->getOperand(0);
} else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
if (GA->mayBeOverridden())
break;
V = GA->getAliasee();
} else {
break;
}
assert(V->getType()->isPointerTy() && "Unexpected operand type!");
} while (Visited.insert(V));
Type *IntPtrTy = TD->getIntPtrType(V->getContext());
return cast<ConstantInt>(ConstantInt::get(IntPtrTy, Offset));
}
/// \brief Analyze a call site for potential inlining.
///
/// Returns true if inlining this call is viable, and false if it is not
/// viable. It computes the cost and adjusts the threshold based on numerous
/// factors and heuristics. If this method returns false but the computed cost
/// is below the computed threshold, then inlining was forcibly disabled by
/// some artifact of the rountine.
bool CallAnalyzer::analyzeCall(CallSite CS) {
++NumCallsAnalyzed;
// Track whether the post-inlining function would have more than one basic
// block. A single basic block is often intended for inlining. Balloon the
// threshold by 50% until we pass the single-BB phase.
bool SingleBB = true;
int SingleBBBonus = Threshold / 2;
Threshold += SingleBBBonus;
// Unless we are always-inlining, perform some tweaks to the cost and
// threshold based on the direct callsite information.
if (!AlwaysInline) {
// We want to more aggressively inline vector-dense kernels, so up the
// threshold, and we'll lower it if the % of vector instructions gets too
// low.
assert(NumInstructions == 0);
assert(NumVectorInstructions == 0);
FiftyPercentVectorBonus = Threshold;
TenPercentVectorBonus = Threshold / 2;
// Give out bonuses per argument, as the instructions setting them up will
// be gone after inlining.
for (unsigned I = 0, E = CS.arg_size(); I != E; ++I) {
if (TD && CS.isByValArgument(I)) {
// We approximate the number of loads and stores needed by dividing the
// size of the byval type by the target's pointer size.
PointerType *PTy = cast<PointerType>(CS.getArgument(I)->getType());
unsigned TypeSize = TD->getTypeSizeInBits(PTy->getElementType());
unsigned PointerSize = TD->getPointerSizeInBits();
// Ceiling division.
unsigned NumStores = (TypeSize + PointerSize - 1) / PointerSize;
// If it generates more than 8 stores it is likely to be expanded as an
// inline memcpy so we take that as an upper bound. Otherwise we assume
// one load and one store per word copied.
// FIXME: The maxStoresPerMemcpy setting from the target should be used
// here instead of a magic number of 8, but it's not available via
// DataLayout.
NumStores = std::min(NumStores, 8U);
Cost -= 2 * NumStores * InlineConstants::InstrCost;
} else {
// For non-byval arguments subtract off one instruction per call
// argument.
Cost -= InlineConstants::InstrCost;
}
}
// If there is only one call of the function, and it has internal linkage,
// the cost of inlining it drops dramatically.
if (F.hasLocalLinkage() && F.hasOneUse() && &F == CS.getCalledFunction())
Cost += InlineConstants::LastCallToStaticBonus;
// If the instruction after the call, or if the normal destination of the
// invoke is an unreachable instruction, the function is noreturn. As such,
// there is little point in inlining this unless there is literally zero
// cost.
Instruction *Instr = CS.getInstruction();
if (InvokeInst *II = dyn_cast<InvokeInst>(Instr)) {
if (isa<UnreachableInst>(II->getNormalDest()->begin()))
Threshold = 1;
} else if (isa<UnreachableInst>(++BasicBlock::iterator(Instr)))
Threshold = 1;
// If this function uses the coldcc calling convention, prefer not to inline
// it.
if (F.getCallingConv() == CallingConv::Cold)
Cost += InlineConstants::ColdccPenalty;
// Check if we're done. This can happen due to bonuses and penalties.
if (Cost > Threshold)
return false;
}
if (F.empty())
return true;
Function *Caller = CS.getInstruction()->getParent()->getParent();
// Check if the caller function is recursive itself.
for (Value::use_iterator U = Caller->use_begin(), E = Caller->use_end();
U != E; ++U) {
CallSite Site(cast<Value>(*U));
if (!Site)
continue;
Instruction *I = Site.getInstruction();
if (I->getParent()->getParent() == Caller) {
IsCallerRecursive = true;
break;
}
}
// Track whether we've seen a return instruction. The first return
// instruction is free, as at least one will usually disappear in inlining.
bool HasReturn = false;
// Populate our simplified values by mapping from function arguments to call
// arguments with known important simplifications.
CallSite::arg_iterator CAI = CS.arg_begin();
for (Function::arg_iterator FAI = F.arg_begin(), FAE = F.arg_end();
FAI != FAE; ++FAI, ++CAI) {
assert(CAI != CS.arg_end());
if (Constant *C = dyn_cast<Constant>(CAI))
SimplifiedValues[FAI] = C;
Value *PtrArg = *CAI;
if (ConstantInt *C = stripAndComputeInBoundsConstantOffsets(PtrArg)) {
ConstantOffsetPtrs[FAI] = std::make_pair(PtrArg, C->getValue());
// We can SROA any pointer arguments derived from alloca instructions.
if (isa<AllocaInst>(PtrArg)) {
SROAArgValues[FAI] = PtrArg;
SROAArgCosts[PtrArg] = 0;
}
}
}
NumConstantArgs = SimplifiedValues.size();
NumConstantOffsetPtrArgs = ConstantOffsetPtrs.size();
NumAllocaArgs = SROAArgValues.size();
// The worklist of live basic blocks in the callee *after* inlining. We avoid
// adding basic blocks of the callee which can be proven to be dead for this
// particular call site in order to get more accurate cost estimates. This
// requires a somewhat heavyweight iteration pattern: we need to walk the
// basic blocks in a breadth-first order as we insert live successors. To
// accomplish this, prioritizing for small iterations because we exit after
// crossing our threshold, we use a small-size optimized SetVector.
typedef SetVector<BasicBlock *, SmallVector<BasicBlock *, 16>,
SmallPtrSet<BasicBlock *, 16> > BBSetVector;
BBSetVector BBWorklist;
BBWorklist.insert(&F.getEntryBlock());
// Note that we *must not* cache the size, this loop grows the worklist.
for (unsigned Idx = 0; Idx != BBWorklist.size(); ++Idx) {
// Bail out the moment we cross the threshold. This means we'll under-count
// the cost, but only when undercounting doesn't matter.
if (!AlwaysInline && Cost > (Threshold + VectorBonus))
break;
BasicBlock *BB = BBWorklist[Idx];
if (BB->empty())
continue;
// Handle the terminator cost here where we can track returns and other
// function-wide constructs.
TerminatorInst *TI = BB->getTerminator();
// We never want to inline functions that contain an indirectbr. This is
// incorrect because all the blockaddress's (in static global initializers
// for example) would be referring to the original function, and this
// indirect jump would jump from the inlined copy of the function into the
// original function which is extremely undefined behavior.
// FIXME: This logic isn't really right; we can safely inline functions
// with indirectbr's as long as no other function or global references the
// blockaddress of a block within the current function. And as a QOI issue,
// if someone is using a blockaddress without an indirectbr, and that
// reference somehow ends up in another function or global, we probably
// don't want to inline this function.
if (isa<IndirectBrInst>(TI))
return false;
if (!HasReturn && isa<ReturnInst>(TI))
HasReturn = true;
else
Cost += InlineConstants::InstrCost;
// Analyze the cost of this block. If we blow through the threshold, this
// returns false, and we can bail on out.
if (!analyzeBlock(BB)) {
if (IsRecursiveCall || ExposesReturnsTwice || HasDynamicAlloca)
return false;
// If the caller is a recursive function then we don't want to inline
// functions which allocate a lot of stack space because it would increase
// the caller stack usage dramatically.
if (IsCallerRecursive &&
AllocatedSize > InlineConstants::TotalAllocaSizeRecursiveCaller)
return false;
break;
}
// Add in the live successors by first checking whether we have terminator
// that may be simplified based on the values simplified by this call.
if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
if (BI->isConditional()) {
Value *Cond = BI->getCondition();
if (ConstantInt *SimpleCond
= dyn_cast_or_null<ConstantInt>(SimplifiedValues.lookup(Cond))) {
BBWorklist.insert(BI->getSuccessor(SimpleCond->isZero() ? 1 : 0));
continue;
}
}
} else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
Value *Cond = SI->getCondition();
if (ConstantInt *SimpleCond
= dyn_cast_or_null<ConstantInt>(SimplifiedValues.lookup(Cond))) {
BBWorklist.insert(SI->findCaseValue(SimpleCond).getCaseSuccessor());
continue;
}
}
// If we're unable to select a particular successor, just count all of
// them.
for (unsigned TIdx = 0, TSize = TI->getNumSuccessors(); TIdx != TSize;
++TIdx)
BBWorklist.insert(TI->getSuccessor(TIdx));
// If we had any successors at this point, than post-inlining is likely to
// have them as well. Note that we assume any basic blocks which existed
// due to branches or switches which folded above will also fold after
// inlining.
if (SingleBB && TI->getNumSuccessors() > 1) {
// Take off the bonus we applied to the threshold.
Threshold -= SingleBBBonus;
SingleBB = false;
}
}
Threshold += VectorBonus;
return AlwaysInline || Cost < Threshold;
}
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
/// \brief Dump stats about this call's analysis.
void CallAnalyzer::dump() {
#define DEBUG_PRINT_STAT(x) llvm::dbgs() << " " #x ": " << x << "\n"
DEBUG_PRINT_STAT(NumConstantArgs);
DEBUG_PRINT_STAT(NumConstantOffsetPtrArgs);
DEBUG_PRINT_STAT(NumAllocaArgs);
DEBUG_PRINT_STAT(NumConstantPtrCmps);
DEBUG_PRINT_STAT(NumConstantPtrDiffs);
DEBUG_PRINT_STAT(NumInstructionsSimplified);
DEBUG_PRINT_STAT(SROACostSavings);
DEBUG_PRINT_STAT(SROACostSavingsLost);
#undef DEBUG_PRINT_STAT
}
#endif
InlineCost InlineCostAnalyzer::getInlineCost(CallSite CS, int Threshold) {
return getInlineCost(CS, CS.getCalledFunction(), Threshold);
}
InlineCost InlineCostAnalyzer::getInlineCost(CallSite CS, Function *Callee,
int Threshold) {
// Don't inline functions which can be redefined at link-time to mean
// something else. Don't inline functions marked noinline or call sites
// marked noinline.
if (!Callee || Callee->mayBeOverridden() ||
Callee->getFnAttributes().hasAttribute(Attributes::NoInline) ||
CS.isNoInline())
return llvm::InlineCost::getNever();
DEBUG(llvm::dbgs() << " Analyzing call of " << Callee->getName()
<< "...\n");
CallAnalyzer CA(TD, *Callee, Threshold);
bool ShouldInline = CA.analyzeCall(CS);
DEBUG(CA.dump());
// Check if there was a reason to force inlining or no inlining.
if (!ShouldInline && CA.getCost() < CA.getThreshold())
return InlineCost::getNever();
if (ShouldInline && (CA.isAlwaysInline() ||
CA.getCost() >= CA.getThreshold()))
return InlineCost::getAlways();
return llvm::InlineCost::get(CA.getCost(), CA.getThreshold());
}