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llvm-project/polly/lib/Support/ScopHelper.cpp
Tobias Grosser b693f42b71 [Polly] Fix code generation of llvm.expect intrinsic 
At the time of code generation, an instruction with an llvm intrinsic is ignored
in copyBB. However, if the value of the instruction is used later in the
program, the value needs to be synthesized. However, this is causing some issues
with the instructions being generated in a hoisted basic block.

Removing llvm.expect from the list of ignored intrinsics fixes this bug.

This resolves http://llvm.org/PR32324.

Contributed-by: Annanay Agarwal <cs14btech11001@iith.ac.in>

Tags: #polly

Differential Revision: https://reviews.llvm.org/D32992

llvm-svn: 303006
2017-05-14 09:09:54 +00:00

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//===- ScopHelper.cpp - Some Helper Functions for Scop. ------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// Small functions that help with Scop and LLVM-IR.
//
//===----------------------------------------------------------------------===//
#include "polly/Support/ScopHelper.h"
#include "polly/Options.h"
#include "polly/ScopInfo.h"
#include "polly/Support/SCEVValidator.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/RegionInfo.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Analysis/ScalarEvolutionExpander.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/Support/Debug.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
using namespace llvm;
using namespace polly;
#define DEBUG_TYPE "polly-scop-helper"
static cl::opt<bool> PollyAllowErrorBlocks(
"polly-allow-error-blocks",
cl::desc("Allow to speculate on the execution of 'error blocks'."),
cl::Hidden, cl::init(true), cl::ZeroOrMore, cl::cat(PollyCategory));
// Ensures that there is just one predecessor to the entry node from outside the
// region.
// The identity of the region entry node is preserved.
static void simplifyRegionEntry(Region *R, DominatorTree *DT, LoopInfo *LI,
RegionInfo *RI) {
BasicBlock *EnteringBB = R->getEnteringBlock();
BasicBlock *Entry = R->getEntry();
// Before (one of):
//
// \ / //
// EnteringBB //
// | \------> //
// \ / | //
// Entry <--\ Entry <--\ //
// / \ / / \ / //
// .... .... //
// Create single entry edge if the region has multiple entry edges.
if (!EnteringBB) {
SmallVector<BasicBlock *, 4> Preds;
for (BasicBlock *P : predecessors(Entry))
if (!R->contains(P))
Preds.push_back(P);
BasicBlock *NewEntering =
SplitBlockPredecessors(Entry, Preds, ".region_entering", DT, LI);
if (RI) {
// The exit block of predecessing regions must be changed to NewEntering
for (BasicBlock *ExitPred : predecessors(NewEntering)) {
Region *RegionOfPred = RI->getRegionFor(ExitPred);
if (RegionOfPred->getExit() != Entry)
continue;
while (!RegionOfPred->isTopLevelRegion() &&
RegionOfPred->getExit() == Entry) {
RegionOfPred->replaceExit(NewEntering);
RegionOfPred = RegionOfPred->getParent();
}
}
// Make all ancestors use EnteringBB as entry; there might be edges to it
Region *AncestorR = R->getParent();
RI->setRegionFor(NewEntering, AncestorR);
while (!AncestorR->isTopLevelRegion() && AncestorR->getEntry() == Entry) {
AncestorR->replaceEntry(NewEntering);
AncestorR = AncestorR->getParent();
}
}
EnteringBB = NewEntering;
}
assert(R->getEnteringBlock() == EnteringBB);
// After:
//
// \ / //
// EnteringBB //
// | //
// | //
// Entry <--\ //
// / \ / //
// .... //
}
// Ensure that the region has a single block that branches to the exit node.
static void simplifyRegionExit(Region *R, DominatorTree *DT, LoopInfo *LI,
RegionInfo *RI) {
BasicBlock *ExitBB = R->getExit();
BasicBlock *ExitingBB = R->getExitingBlock();
// Before:
//
// (Region) ______/ //
// \ | / //
// ExitBB //
// / \ //
if (!ExitingBB) {
SmallVector<BasicBlock *, 4> Preds;
for (BasicBlock *P : predecessors(ExitBB))
if (R->contains(P))
Preds.push_back(P);
// Preds[0] Preds[1] otherBB //
// \ | ________/ //
// \ | / //
// BB //
ExitingBB =
SplitBlockPredecessors(ExitBB, Preds, ".region_exiting", DT, LI);
// Preds[0] Preds[1] otherBB //
// \ / / //
// BB.region_exiting / //
// \ / //
// BB //
if (RI)
RI->setRegionFor(ExitingBB, R);
// Change the exit of nested regions, but not the region itself,
R->replaceExitRecursive(ExitingBB);
R->replaceExit(ExitBB);
}
assert(ExitingBB == R->getExitingBlock());
// After:
//
// \ / //
// ExitingBB _____/ //
// \ / //
// ExitBB //
// / \ //
}
void polly::simplifyRegion(Region *R, DominatorTree *DT, LoopInfo *LI,
RegionInfo *RI) {
assert(R && !R->isTopLevelRegion());
assert(!RI || RI == R->getRegionInfo());
assert((!RI || DT) &&
"RegionInfo requires DominatorTree to be updated as well");
simplifyRegionEntry(R, DT, LI, RI);
simplifyRegionExit(R, DT, LI, RI);
assert(R->isSimple());
}
// Split the block into two successive blocks.
//
// Like llvm::SplitBlock, but also preserves RegionInfo
static BasicBlock *splitBlock(BasicBlock *Old, Instruction *SplitPt,
DominatorTree *DT, llvm::LoopInfo *LI,
RegionInfo *RI) {
assert(Old && SplitPt);
// Before:
//
// \ / //
// Old //
// / \ //
BasicBlock *NewBlock = llvm::SplitBlock(Old, SplitPt, DT, LI);
if (RI) {
Region *R = RI->getRegionFor(Old);
RI->setRegionFor(NewBlock, R);
}
// After:
//
// \ / //
// Old //
// | //
// NewBlock //
// / \ //
return NewBlock;
}
void polly::splitEntryBlockForAlloca(BasicBlock *EntryBlock, Pass *P) {
// Find first non-alloca instruction. Every basic block has a non-alloc
// instruction, as every well formed basic block has a terminator.
BasicBlock::iterator I = EntryBlock->begin();
while (isa<AllocaInst>(I))
++I;
auto *DTWP = P->getAnalysisIfAvailable<DominatorTreeWrapperPass>();
auto *DT = DTWP ? &DTWP->getDomTree() : nullptr;
auto *LIWP = P->getAnalysisIfAvailable<LoopInfoWrapperPass>();
auto *LI = LIWP ? &LIWP->getLoopInfo() : nullptr;
RegionInfoPass *RIP = P->getAnalysisIfAvailable<RegionInfoPass>();
RegionInfo *RI = RIP ? &RIP->getRegionInfo() : nullptr;
// splitBlock updates DT, LI and RI.
splitBlock(EntryBlock, &*I, DT, LI, RI);
}
/// The SCEVExpander will __not__ generate any code for an existing SDiv/SRem
/// instruction but just use it, if it is referenced as a SCEVUnknown. We want
/// however to generate new code if the instruction is in the analyzed region
/// and we generate code outside/in front of that region. Hence, we generate the
/// code for the SDiv/SRem operands in front of the analyzed region and then
/// create a new SDiv/SRem operation there too.
struct ScopExpander : SCEVVisitor<ScopExpander, const SCEV *> {
friend struct SCEVVisitor<ScopExpander, const SCEV *>;
explicit ScopExpander(const Region &R, ScalarEvolution &SE,
const DataLayout &DL, const char *Name, ValueMapT *VMap,
BasicBlock *RTCBB)
: Expander(SCEVExpander(SE, DL, Name)), SE(SE), Name(Name), R(R),
VMap(VMap), RTCBB(RTCBB) {}
Value *expandCodeFor(const SCEV *E, Type *Ty, Instruction *I) {
// If we generate code in the region we will immediately fall back to the
// SCEVExpander, otherwise we will stop at all unknowns in the SCEV and if
// needed replace them by copies computed in the entering block.
if (!R.contains(I))
E = visit(E);
return Expander.expandCodeFor(E, Ty, I);
}
private:
SCEVExpander Expander;
ScalarEvolution &SE;
const char *Name;
const Region &R;
ValueMapT *VMap;
BasicBlock *RTCBB;
const SCEV *visitGenericInst(const SCEVUnknown *E, Instruction *Inst,
Instruction *IP) {
if (!Inst || !R.contains(Inst))
return E;
assert(!Inst->mayThrow() && !Inst->mayReadOrWriteMemory() &&
!isa<PHINode>(Inst));
auto *InstClone = Inst->clone();
for (auto &Op : Inst->operands()) {
assert(SE.isSCEVable(Op->getType()));
auto *OpSCEV = SE.getSCEV(Op);
auto *OpClone = expandCodeFor(OpSCEV, Op->getType(), IP);
InstClone->replaceUsesOfWith(Op, OpClone);
}
InstClone->setName(Name + Inst->getName());
InstClone->insertBefore(IP);
return SE.getSCEV(InstClone);
}
const SCEV *visitUnknown(const SCEVUnknown *E) {
// If a value mapping was given try if the underlying value is remapped.
Value *NewVal = VMap ? VMap->lookup(E->getValue()) : nullptr;
if (NewVal) {
auto *NewE = SE.getSCEV(NewVal);
// While the mapped value might be different the SCEV representation might
// not be. To this end we will check before we go into recursion here.
if (E != NewE)
return visit(NewE);
}
Instruction *Inst = dyn_cast<Instruction>(E->getValue());
Instruction *IP;
if (Inst && !R.contains(Inst))
IP = Inst;
else if (Inst && RTCBB->getParent() == Inst->getFunction())
IP = RTCBB->getTerminator();
else
IP = RTCBB->getParent()->getEntryBlock().getTerminator();
if (!Inst || (Inst->getOpcode() != Instruction::SRem &&
Inst->getOpcode() != Instruction::SDiv))
return visitGenericInst(E, Inst, IP);
const SCEV *LHSScev = SE.getSCEV(Inst->getOperand(0));
const SCEV *RHSScev = SE.getSCEV(Inst->getOperand(1));
if (!SE.isKnownNonZero(RHSScev))
RHSScev = SE.getUMaxExpr(RHSScev, SE.getConstant(E->getType(), 1));
Value *LHS = expandCodeFor(LHSScev, E->getType(), IP);
Value *RHS = expandCodeFor(RHSScev, E->getType(), IP);
Inst = BinaryOperator::Create((Instruction::BinaryOps)Inst->getOpcode(),
LHS, RHS, Inst->getName() + Name, IP);
return SE.getSCEV(Inst);
}
/// The following functions will just traverse the SCEV and rebuild it with
/// the new operands returned by the traversal.
///
///{
const SCEV *visitConstant(const SCEVConstant *E) { return E; }
const SCEV *visitTruncateExpr(const SCEVTruncateExpr *E) {
return SE.getTruncateExpr(visit(E->getOperand()), E->getType());
}
const SCEV *visitZeroExtendExpr(const SCEVZeroExtendExpr *E) {
return SE.getZeroExtendExpr(visit(E->getOperand()), E->getType());
}
const SCEV *visitSignExtendExpr(const SCEVSignExtendExpr *E) {
return SE.getSignExtendExpr(visit(E->getOperand()), E->getType());
}
const SCEV *visitUDivExpr(const SCEVUDivExpr *E) {
auto *RHSScev = visit(E->getRHS());
if (!SE.isKnownNonZero(RHSScev))
RHSScev = SE.getUMaxExpr(RHSScev, SE.getConstant(E->getType(), 1));
return SE.getUDivExpr(visit(E->getLHS()), RHSScev);
}
const SCEV *visitAddExpr(const SCEVAddExpr *E) {
SmallVector<const SCEV *, 4> NewOps;
for (const SCEV *Op : E->operands())
NewOps.push_back(visit(Op));
return SE.getAddExpr(NewOps);
}
const SCEV *visitMulExpr(const SCEVMulExpr *E) {
SmallVector<const SCEV *, 4> NewOps;
for (const SCEV *Op : E->operands())
NewOps.push_back(visit(Op));
return SE.getMulExpr(NewOps);
}
const SCEV *visitUMaxExpr(const SCEVUMaxExpr *E) {
SmallVector<const SCEV *, 4> NewOps;
for (const SCEV *Op : E->operands())
NewOps.push_back(visit(Op));
return SE.getUMaxExpr(NewOps);
}
const SCEV *visitSMaxExpr(const SCEVSMaxExpr *E) {
SmallVector<const SCEV *, 4> NewOps;
for (const SCEV *Op : E->operands())
NewOps.push_back(visit(Op));
return SE.getSMaxExpr(NewOps);
}
const SCEV *visitAddRecExpr(const SCEVAddRecExpr *E) {
SmallVector<const SCEV *, 4> NewOps;
for (const SCEV *Op : E->operands())
NewOps.push_back(visit(Op));
return SE.getAddRecExpr(NewOps, E->getLoop(), E->getNoWrapFlags());
}
///}
};
Value *polly::expandCodeFor(Scop &S, ScalarEvolution &SE, const DataLayout &DL,
const char *Name, const SCEV *E, Type *Ty,
Instruction *IP, ValueMapT *VMap,
BasicBlock *RTCBB) {
ScopExpander Expander(S.getRegion(), SE, DL, Name, VMap, RTCBB);
return Expander.expandCodeFor(E, Ty, IP);
}
bool polly::isErrorBlock(BasicBlock &BB, const Region &R, LoopInfo &LI,
const DominatorTree &DT) {
if (!PollyAllowErrorBlocks)
return false;
if (isa<UnreachableInst>(BB.getTerminator()))
return true;
if (LI.isLoopHeader(&BB))
return false;
// Basic blocks that are always executed are not considered error blocks,
// as their execution can not be a rare event.
bool DominatesAllPredecessors = true;
for (auto Pred : predecessors(R.getExit()))
if (R.contains(Pred) && !DT.dominates(&BB, Pred))
DominatesAllPredecessors = false;
if (DominatesAllPredecessors)
return false;
// FIXME: This is a simple heuristic to determine if the load is executed
// in a conditional. However, we actually would need the control
// condition, i.e., the post dominance frontier. Alternatively we
// could walk up the dominance tree until we find a block that is
// not post dominated by the load and check if it is a conditional
// or a loop header.
auto *DTNode = DT.getNode(&BB);
auto *IDomBB = DTNode->getIDom()->getBlock();
if (LI.isLoopHeader(IDomBB))
return false;
for (Instruction &Inst : BB)
if (CallInst *CI = dyn_cast<CallInst>(&Inst)) {
if (isIgnoredIntrinsic(CI))
return false;
if (!CI->doesNotAccessMemory())
return true;
if (CI->doesNotReturn())
return true;
}
return false;
}
Value *polly::getConditionFromTerminator(TerminatorInst *TI) {
if (BranchInst *BR = dyn_cast<BranchInst>(TI)) {
if (BR->isUnconditional())
return ConstantInt::getTrue(Type::getInt1Ty(TI->getContext()));
return BR->getCondition();
}
if (SwitchInst *SI = dyn_cast<SwitchInst>(TI))
return SI->getCondition();
return nullptr;
}
bool polly::isHoistableLoad(LoadInst *LInst, Region &R, LoopInfo &LI,
ScalarEvolution &SE, const DominatorTree &DT) {
Loop *L = LI.getLoopFor(LInst->getParent());
auto *Ptr = LInst->getPointerOperand();
const SCEV *PtrSCEV = SE.getSCEVAtScope(Ptr, L);
while (L && R.contains(L)) {
if (!SE.isLoopInvariant(PtrSCEV, L))
return false;
L = L->getParentLoop();
}
for (auto *User : Ptr->users()) {
auto *UserI = dyn_cast<Instruction>(User);
if (!UserI || !R.contains(UserI))
continue;
if (!UserI->mayWriteToMemory())
continue;
auto &BB = *UserI->getParent();
if (DT.dominates(&BB, LInst->getParent()))
return false;
bool DominatesAllPredecessors = true;
for (auto Pred : predecessors(R.getExit()))
if (R.contains(Pred) && !DT.dominates(&BB, Pred))
DominatesAllPredecessors = false;
if (!DominatesAllPredecessors)
continue;
return false;
}
return true;
}
bool polly::isIgnoredIntrinsic(const Value *V) {
if (auto *IT = dyn_cast<IntrinsicInst>(V)) {
switch (IT->getIntrinsicID()) {
// Lifetime markers are supported/ignored.
case llvm::Intrinsic::lifetime_start:
case llvm::Intrinsic::lifetime_end:
// Invariant markers are supported/ignored.
case llvm::Intrinsic::invariant_start:
case llvm::Intrinsic::invariant_end:
// Some misc annotations are supported/ignored.
case llvm::Intrinsic::var_annotation:
case llvm::Intrinsic::ptr_annotation:
case llvm::Intrinsic::annotation:
case llvm::Intrinsic::donothing:
case llvm::Intrinsic::assume:
// Some debug info intrisics are supported/ignored.
case llvm::Intrinsic::dbg_value:
case llvm::Intrinsic::dbg_declare:
return true;
default:
break;
}
}
return false;
}
bool polly::canSynthesize(const Value *V, const Scop &S, ScalarEvolution *SE,
Loop *Scope) {
if (!V || !SE->isSCEVable(V->getType()))
return false;
if (const SCEV *Scev = SE->getSCEVAtScope(const_cast<Value *>(V), Scope))
if (!isa<SCEVCouldNotCompute>(Scev))
if (!hasScalarDepsInsideRegion(Scev, &S.getRegion(), Scope, false))
return true;
return false;
}
llvm::BasicBlock *polly::getUseBlock(llvm::Use &U) {
Instruction *UI = dyn_cast<Instruction>(U.getUser());
if (!UI)
return nullptr;
if (PHINode *PHI = dyn_cast<PHINode>(UI))
return PHI->getIncomingBlock(U);
return UI->getParent();
}
std::tuple<std::vector<const SCEV *>, std::vector<int>>
polly::getIndexExpressionsFromGEP(GetElementPtrInst *GEP, ScalarEvolution &SE) {
std::vector<const SCEV *> Subscripts;
std::vector<int> Sizes;
Type *Ty = GEP->getPointerOperandType();
bool DroppedFirstDim = false;
for (unsigned i = 1; i < GEP->getNumOperands(); i++) {
const SCEV *Expr = SE.getSCEV(GEP->getOperand(i));
if (i == 1) {
if (auto *PtrTy = dyn_cast<PointerType>(Ty)) {
Ty = PtrTy->getElementType();
} else if (auto *ArrayTy = dyn_cast<ArrayType>(Ty)) {
Ty = ArrayTy->getElementType();
} else {
Subscripts.clear();
Sizes.clear();
break;
}
if (auto *Const = dyn_cast<SCEVConstant>(Expr))
if (Const->getValue()->isZero()) {
DroppedFirstDim = true;
continue;
}
Subscripts.push_back(Expr);
continue;
}
auto *ArrayTy = dyn_cast<ArrayType>(Ty);
if (!ArrayTy) {
Subscripts.clear();
Sizes.clear();
break;
}
Subscripts.push_back(Expr);
if (!(DroppedFirstDim && i == 2))
Sizes.push_back(ArrayTy->getNumElements());
Ty = ArrayTy->getElementType();
}
return std::make_tuple(Subscripts, Sizes);
}
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