maxjhandsome
/
llvm-project
forked from OSchip/llvm-project
1
0
Fork 0
Code Issues Pull Requests Packages Releases Wiki Activity
llvm-project/llvm/lib/Transforms/Scalar/AlignmentFromAssumptions.cpp

361 lines
14 KiB
C++
Raw Blame History

//===----------------------- AlignmentFromAssumptions.cpp -----------------===//
// Set Load/Store Alignments From Assumptions
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implements a ScalarEvolution-based transformation to set
// the alignments of load, stores and memory intrinsics based on the truth
// expressions of assume intrinsics. The primary motivation is to handle
// complex alignment assumptions that apply to vector loads and stores that
// appear after vectorization and unrolling.
//
//===----------------------------------------------------------------------===//
#include "llvm/IR/Instructions.h"
#include "llvm/InitializePasses.h"
#include "llvm/Transforms/Scalar/AlignmentFromAssumptions.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Scalar.h"
#define AA_NAME "alignment-from-assumptions"
#define DEBUG_TYPE AA_NAME
using namespace llvm;
STATISTIC(NumLoadAlignChanged,
"Number of loads changed by alignment assumptions");
STATISTIC(NumStoreAlignChanged,
"Number of stores changed by alignment assumptions");
STATISTIC(NumMemIntAlignChanged,
"Number of memory intrinsics changed by alignment assumptions");
namespace {
struct AlignmentFromAssumptions : public FunctionPass {
static char ID; // Pass identification, replacement for typeid
AlignmentFromAssumptions() : FunctionPass(ID) {
initializeAlignmentFromAssumptionsPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F) override;
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<AssumptionCacheTracker>();
AU.addRequired<ScalarEvolutionWrapperPass>();
AU.addRequired<DominatorTreeWrapperPass>();
AU.setPreservesCFG();
AU.addPreserved<AAResultsWrapperPass>();
AU.addPreserved<GlobalsAAWrapperPass>();
AU.addPreserved<LoopInfoWrapperPass>();
AU.addPreserved<DominatorTreeWrapperPass>();
AU.addPreserved<ScalarEvolutionWrapperPass>();
}
AlignmentFromAssumptionsPass Impl;
};
}
char AlignmentFromAssumptions::ID = 0;
static const char aip_name[] = "Alignment from assumptions";
INITIALIZE_PASS_BEGIN(AlignmentFromAssumptions, AA_NAME,
aip_name, false, false)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
INITIALIZE_PASS_END(AlignmentFromAssumptions, AA_NAME,
aip_name, false, false)
FunctionPass *llvm::createAlignmentFromAssumptionsPass() {
return new AlignmentFromAssumptions();
}
// Given an expression for the (constant) alignment, AlignSCEV, and an
// expression for the displacement between a pointer and the aligned address,
// DiffSCEV, compute the alignment of the displaced pointer if it can be reduced
// to a constant. Using SCEV to compute alignment handles the case where
// DiffSCEV is a recurrence with constant start such that the aligned offset
// is constant. e.g. {16,+,32} % 32 -> 16.
static MaybeAlign getNewAlignmentDiff(const SCEV *DiffSCEV,
const SCEV *AlignSCEV,
ScalarEvolution *SE) {
// DiffUnits = Diff % int64_t(Alignment)
const SCEV *DiffUnitsSCEV = SE->getURemExpr(DiffSCEV, AlignSCEV);
LLVM_DEBUG(dbgs() << "\talignment relative to " << *AlignSCEV << " is "
<< *DiffUnitsSCEV << " (diff: " << *DiffSCEV << ")\n");
if (const SCEVConstant *ConstDUSCEV =
dyn_cast<SCEVConstant>(DiffUnitsSCEV)) {
int64_t DiffUnits = ConstDUSCEV->getValue()->getSExtValue();
// If the displacement is an exact multiple of the alignment, then the
// displaced pointer has the same alignment as the aligned pointer, so
// return the alignment value.
if (!DiffUnits)
return cast<SCEVConstant>(AlignSCEV)->getValue()->getAlignValue();
// If the displacement is not an exact multiple, but the remainder is a
// constant, then return this remainder (but only if it is a power of 2).
uint64_t DiffUnitsAbs = std::abs(DiffUnits);
if (isPowerOf2_64(DiffUnitsAbs))
return Align(DiffUnitsAbs);
}
return None;
}
// There is an address given by an offset OffSCEV from AASCEV which has an
// alignment AlignSCEV. Use that information, if possible, to compute a new
// alignment for Ptr.
static Align getNewAlignment(const SCEV *AASCEV, const SCEV *AlignSCEV,
const SCEV *OffSCEV, Value *Ptr,
ScalarEvolution *SE) {
const SCEV *PtrSCEV = SE->getSCEV(Ptr);
// On a platform with 32-bit allocas, but 64-bit flat/global pointer sizes
// (*cough* AMDGPU), the effective SCEV type of AASCEV and PtrSCEV
// may disagree. Trunc/extend so they agree.
PtrSCEV = SE->getTruncateOrZeroExtend(
PtrSCEV, SE->getEffectiveSCEVType(AASCEV->getType()));
const SCEV *DiffSCEV = SE->getMinusSCEV(PtrSCEV, AASCEV);
if (isa<SCEVCouldNotCompute>(DiffSCEV))
return Align(1);
// On 32-bit platforms, DiffSCEV might now have type i32 -- we've always
// sign-extended OffSCEV to i64, so make sure they agree again.
DiffSCEV = SE->getNoopOrSignExtend(DiffSCEV, OffSCEV->getType());
// What we really want to know is the overall offset to the aligned
// address. This address is displaced by the provided offset.
DiffSCEV = SE->getAddExpr(DiffSCEV, OffSCEV);
LLVM_DEBUG(dbgs() << "AFI: alignment of " << *Ptr << " relative to "
<< *AlignSCEV << " and offset " << *OffSCEV
<< " using diff " << *DiffSCEV << "\n");
if (MaybeAlign NewAlignment = getNewAlignmentDiff(DiffSCEV, AlignSCEV, SE)) {
LLVM_DEBUG(dbgs() << "\tnew alignment: " << DebugStr(NewAlignment) << "\n");
return *NewAlignment;
}
if (const SCEVAddRecExpr *DiffARSCEV = dyn_cast<SCEVAddRecExpr>(DiffSCEV)) {
// The relative offset to the alignment assumption did not yield a constant,
// but we should try harder: if we assume that a is 32-byte aligned, then in
// for (i = 0; i < 1024; i += 4) r += a[i]; not all of the loads from a are
// 32-byte aligned, but instead alternate between 32 and 16-byte alignment.
// As a result, the new alignment will not be a constant, but can still
// be improved over the default (of 4) to 16.
const SCEV *DiffStartSCEV = DiffARSCEV->getStart();
const SCEV *DiffIncSCEV = DiffARSCEV->getStepRecurrence(*SE);
LLVM_DEBUG(dbgs() << "\ttrying start/inc alignment using start "
<< *DiffStartSCEV << " and inc " << *DiffIncSCEV << "\n");
// Now compute the new alignment using the displacement to the value in the
// first iteration, and also the alignment using the per-iteration delta.
// If these are the same, then use that answer. Otherwise, use the smaller
// one, but only if it divides the larger one.
MaybeAlign NewAlignment = getNewAlignmentDiff(DiffStartSCEV, AlignSCEV, SE);
MaybeAlign NewIncAlignment =
getNewAlignmentDiff(DiffIncSCEV, AlignSCEV, SE);
LLVM_DEBUG(dbgs() << "\tnew start alignment: " << DebugStr(NewAlignment)
<< "\n");
LLVM_DEBUG(dbgs() << "\tnew inc alignment: " << DebugStr(NewIncAlignment)
<< "\n");
if (!NewAlignment || !NewIncAlignment)
return Align(1);
const Align NewAlign = *NewAlignment;
const Align NewIncAlign = *NewIncAlignment;
if (NewAlign > NewIncAlign) {
LLVM_DEBUG(dbgs() << "\tnew start/inc alignment: "
<< DebugStr(NewIncAlign) << "\n");
return NewIncAlign;
}
if (NewIncAlign > NewAlign) {
LLVM_DEBUG(dbgs() << "\tnew start/inc alignment: " << DebugStr(NewAlign)
<< "\n");
return NewAlign;
}
assert(NewIncAlign == NewAlign);
LLVM_DEBUG(dbgs() << "\tnew start/inc alignment: " << DebugStr(NewAlign)
<< "\n");
return NewAlign;
}
return Align(1);
}
bool AlignmentFromAssumptionsPass::extractAlignmentInfo(CallInst *I,
unsigned Idx,
Value *&AAPtr,
const SCEV *&AlignSCEV,
const SCEV *&OffSCEV) {
Type *Int64Ty = Type::getInt64Ty(I->getContext());
OperandBundleUse AlignOB = I->getOperandBundleAt(Idx);
if (AlignOB.getTagName() != "align")
return false;
assert(AlignOB.Inputs.size() >= 2);
AAPtr = AlignOB.Inputs[0].get();
// TODO: Consider accumulating the offset to the base.
AAPtr = AAPtr->stripPointerCastsSameRepresentation();
AlignSCEV = SE->getSCEV(AlignOB.Inputs[1].get());
AlignSCEV = SE->getTruncateOrZeroExtend(AlignSCEV, Int64Ty);
if (AlignOB.Inputs.size() == 3)
OffSCEV = SE->getSCEV(AlignOB.Inputs[2].get());
else
OffSCEV = SE->getZero(Int64Ty);
OffSCEV = SE->getTruncateOrZeroExtend(OffSCEV, Int64Ty);
return true;
}
bool AlignmentFromAssumptionsPass::processAssumption(CallInst *ACall,
unsigned Idx) {
Value *AAPtr;
const SCEV *AlignSCEV, *OffSCEV;
if (!extractAlignmentInfo(ACall, Idx, AAPtr, AlignSCEV, OffSCEV))
return false;
// Skip ConstantPointerNull and UndefValue. Assumptions on these shouldn't
// affect other users.
if (isa<ConstantData>(AAPtr))
return false;
const SCEV *AASCEV = SE->getSCEV(AAPtr);
// Apply the assumption to all other users of the specified pointer.
SmallPtrSet<Instruction *, 32> Visited;
SmallVector<Instruction*, 16> WorkList;
for (User *J : AAPtr->users()) {
if (J == ACall)
continue;
if (Instruction *K = dyn_cast<Instruction>(J))
WorkList.push_back(K);
}
while (!WorkList.empty()) {
Instruction *J = WorkList.pop_back_val();
if (LoadInst *LI = dyn_cast<LoadInst>(J)) {
if (!isValidAssumeForContext(ACall, J, DT))
continue;
Align NewAlignment = getNewAlignment(AASCEV, AlignSCEV, OffSCEV,
LI->getPointerOperand(), SE);
if (NewAlignment > LI->getAlign()) {
LI->setAlignment(NewAlignment);
++NumLoadAlignChanged;
}
} else if (StoreInst *SI = dyn_cast<StoreInst>(J)) {
if (!isValidAssumeForContext(ACall, J, DT))
continue;
Align NewAlignment = getNewAlignment(AASCEV, AlignSCEV, OffSCEV,
SI->getPointerOperand(), SE);
if (NewAlignment > SI->getAlign()) {
SI->setAlignment(NewAlignment);
++NumStoreAlignChanged;
}
} else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(J)) {
if (!isValidAssumeForContext(ACall, J, DT))
continue;
Align NewDestAlignment =
getNewAlignment(AASCEV, AlignSCEV, OffSCEV, MI->getDest(), SE);
LLVM_DEBUG(dbgs() << "\tmem inst: " << DebugStr(NewDestAlignment)
<< "\n";);
if (NewDestAlignment > *MI->getDestAlign()) {
MI->setDestAlignment(NewDestAlignment);
++NumMemIntAlignChanged;
}
// For memory transfers, there is also a source alignment that
// can be set.
if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI)) {
Align NewSrcAlignment =
getNewAlignment(AASCEV, AlignSCEV, OffSCEV, MTI->getSource(), SE);
LLVM_DEBUG(dbgs() << "\tmem trans: " << DebugStr(NewSrcAlignment)
<< "\n";);
if (NewSrcAlignment > *MTI->getSourceAlign()) {
MTI->setSourceAlignment(NewSrcAlignment);
++NumMemIntAlignChanged;
}
}
}
// Now that we've updated that use of the pointer, look for other uses of
// the pointer to update.
Visited.insert(J);
for (User *UJ : J->users()) {
Instruction *K = cast<Instruction>(UJ);
if (!Visited.count(K))
WorkList.push_back(K);
}
}
return true;
}
bool AlignmentFromAssumptions::runOnFunction(Function &F) {
if (skipFunction(F))
return false;
auto &AC = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
ScalarEvolution *SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
DominatorTree *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
return Impl.runImpl(F, AC, SE, DT);
}
bool AlignmentFromAssumptionsPass::runImpl(Function &F, AssumptionCache &AC,
ScalarEvolution *SE_,
DominatorTree *DT_) {
SE = SE_;
DT = DT_;
bool Changed = false;
for (auto &AssumeVH : AC.assumptions())
if (AssumeVH) {
CallInst *Call = cast<CallInst>(AssumeVH);
for (unsigned Idx = 0; Idx < Call->getNumOperandBundles(); Idx++)
Changed |= processAssumption(Call, Idx);
}
return Changed;
}
PreservedAnalyses
AlignmentFromAssumptionsPass::run(Function &F, FunctionAnalysisManager &AM) {
AssumptionCache &AC = AM.getResult<AssumptionAnalysis>(F);
ScalarEvolution &SE = AM.getResult<ScalarEvolutionAnalysis>(F);
DominatorTree &DT = AM.getResult<DominatorTreeAnalysis>(F);
if (!runImpl(F, AC, &SE, &DT))
return PreservedAnalyses::all();
PreservedAnalyses PA;
PA.preserveSet<CFGAnalyses>();
PA.preserve<ScalarEvolutionAnalysis>();
return PA;
}
Reference in New Issue View Git Blame Copy Permalink