[llvm] r316054 - [ScalarEvolution] Handling for ICmp occuring in the evolution chain.
Jatin Bhateja via llvm-commits
llvm-commits at lists.llvm.org
Tue Oct 17 22:19:48 PDT 2017
It was accepted by one reviewer which is why it was landed as per policy.
We can do a post commit review also as per developer's policy.
Do let me know what comments you have and it could be incorporated.
On 18 Oct 2017 10:22, "Sanjoy Das" <sanjoy at playingwithpointers.com> wrote:
> Hi Jatin,
>
> This hasn't been LGTMed. Please revert it for now while we continue the
> review.
>
> -- Sanjoy
>
> On Tue, Oct 17, 2017 at 6:36 PM Jatin Bhateja via llvm-commits <
> llvm-commits at lists.llvm.org> wrote:
>
>> Author: jbhateja
>> Date: Tue Oct 17 18:36:16 2017
>> New Revision: 316054
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=316054&view=rev
>> Log:
>> [ScalarEvolution] Handling for ICmp occuring in the evolution chain.
>>
>> Summary:
>> If a compare instruction is same or inverse of the compare in the
>> branch of the loop latch, then return a constant evolution node.
>> Currently scope of evaluation is limited to SCEV computation for
>> PHI nodes.
>>
>> This shall facilitate computations of loop exit counts in cases
>> where compare appears in the evolution chain of induction variables.
>>
>> Will fix PR 34538
>> Reviewers: sanjoy, hfinkel, junryoungju
>>
>> Reviewed By: junryoungju
>>
>> Subscribers: javed.absar, llvm-commits
>>
>> Differential Revision: https://reviews.llvm.org/D38494
>>
>> Added:
>> llvm/trunk/test/Analysis/ScalarEvolution/pr34538.ll
>> Modified:
>> llvm/trunk/include/llvm/Analysis/ScalarEvolution.h
>> llvm/trunk/lib/Analysis/ScalarEvolution.cpp
>> llvm/trunk/lib/Transforms/Scalar/LoopStrengthReduce.cpp
>>
>> Modified: llvm/trunk/include/llvm/Analysis/ScalarEvolution.h
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/
>> Analysis/ScalarEvolution.h?rev=316054&r1=316053&r2=316054&view=diff
>> ============================================================
>> ==================
>> --- llvm/trunk/include/llvm/Analysis/ScalarEvolution.h (original)
>> +++ llvm/trunk/include/llvm/Analysis/ScalarEvolution.h Tue Oct 17
>> 18:36:16 2017
>> @@ -1378,6 +1378,9 @@ private:
>> /// Helper function called from createNodeForPHI.
>> const SCEV *createAddRecFromPHI(PHINode *PN);
>>
>> + /// Evaluate ICmpInst to a constant node for special patterns.
>> + const SCEV *evaluateForICmp(ICmpInst *IC);
>> +
>> /// A helper function for createAddRecFromPHI to handle simple cases.
>> const SCEV *createSimpleAffineAddRec(PHINode *PN, Value *BEValueV,
>> Value *StartValueV);
>>
>> Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/
>> ScalarEvolution.cpp?rev=316054&r1=316053&r2=316054&view=diff
>> ============================================================
>> ==================
>> --- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
>> +++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Tue Oct 17 18:36:16 2017
>> @@ -4756,11 +4756,26 @@ const SCEV *ScalarEvolution::createAddRe
>> Ops.push_back(Add->getOperand(i));
>> const SCEV *Accum = getAddExpr(Ops);
>>
>> + bool InvariantF = isLoopInvariant(Accum, L);
>> +
>> + if (!InvariantF && Accum->getSCEVType() == scZeroExtend) {
>> + const SCEV *Op = dyn_cast<SCEVZeroExtendExpr>(A
>> ccum)->getOperand();
>> + const SCEVUnknown *Un = dyn_cast<SCEVUnknown>(Op);
>> + if (Un && Un->getValue() && isa<Instruction>(Un->getValue()) &&
>> + dyn_cast<Instruction>(Un->getValue())->getOpcode() ==
>> + Instruction::ICmp) {
>> + const SCEV *ICmpSC = evaluateForICmp(cast<ICmpInst>
>> (Un->getValue()));
>> + bool IsConstSC = ICmpSC->getSCEVType() == scConstant;
>> + Accum =
>> + IsConstSC ? getZeroExtendExpr(ICmpSC, Accum->getType()) :
>> Accum;
>> + InvariantF = IsConstSC ? true : false;
>> + }
>> + }
>> +
>> // This is not a valid addrec if the step amount is varying each
>> // loop iteration, but is not itself an addrec in this loop.
>> - if (isLoopInvariant(Accum, L) ||
>> - (isa<SCEVAddRecExpr>(Accum) &&
>> - cast<SCEVAddRecExpr>(Accum)->getLoop() == L)) {
>> + if (InvariantF || (isa<SCEVAddRecExpr>(Accum) &&
>> + cast<SCEVAddRecExpr>(Accum)->getLoop() == L)) {
>> SCEV::NoWrapFlags Flags = SCEV::FlagAnyWrap;
>>
>> if (auto BO = MatchBinaryOp(BEValueV, DT)) {
>> @@ -6443,6 +6458,30 @@ void ScalarEvolution::forgetLoop(const L
>> }
>> }
>>
>> +
>> +const SCEV *ScalarEvolution::evaluateForICmp(ICmpInst *IC) {
>> + BasicBlock *Latch = nullptr;
>> + const Loop *L = LI.getLoopFor(IC->getParent());
>> +
>> + // If compare instruction is same or inverse of the compare in the
>> + // branch of the loop latch, then return a constant evolution
>> + // node. This shall facilitate computations of loop exit counts
>> + // in cases where compare appears in the evolution chain of induction
>> + // variables.
>> + if (L && (Latch = L->getLoopLatch())) {
>> + BranchInst *BI = dyn_cast<BranchInst>(Latch->getTerminator());
>> + if (BI && BI->isConditional() && BI->getCondition() == IC) {
>> + if (BI->getSuccessor(0) != L->getHeader())
>> + return getZero(Type::getInt1Ty(getContext()));
>> + else
>> + return getOne(Type::getInt1Ty(getContext()));
>> + }
>> + }
>> +
>> + return getUnknown(IC);
>> +}
>> +
>> +
>> void ScalarEvolution::forgetValue(Value *V) {
>> Instruction *I = dyn_cast<Instruction>(V);
>> if (!I) return;
>>
>> Modified: llvm/trunk/lib/Transforms/Scalar/LoopStrengthReduce.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transform
>> s/Scalar/LoopStrengthReduce.cpp?rev=316054&r1=316053&r2=316054&view=diff
>> ============================================================
>> ==================
>> --- llvm/trunk/lib/Transforms/Scalar/LoopStrengthReduce.cpp (original)
>> +++ llvm/trunk/lib/Transforms/Scalar/LoopStrengthReduce.cpp Tue Oct 17
>> 18:36:16 2017
>> @@ -2973,8 +2973,11 @@ void LSRInstance::CollectChains() {
>> // Ignore users that are part of a SCEV expression. This way we
>> only
>> // consider leaf IV Users. This effectively rediscovers a portion
>> of
>> // IVUsers analysis but in program order this time.
>> - if (SE.isSCEVable(I.getType()) && !isa<SCEVUnknown>(SE.getSCEV(&
>> I)))
>> - continue;
>> + if (SE.isSCEVable(I.getType())) {
>> + const SCEV *SI = SE.getSCEV(&I);
>> + if (!isa<SCEVUnknown>(SI) && !isa<SCEVConstant>(SI))
>> + continue;
>> + }
>>
>> // Remove this instruction from any NearUsers set it may be in.
>> for (unsigned ChainIdx = 0, NChains = IVChainVec.size();
>>
>> Added: llvm/trunk/test/Analysis/ScalarEvolution/pr34538.ll
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis
>> /ScalarEvolution/pr34538.ll?rev=316054&view=auto
>> ============================================================
>> ==================
>> --- llvm/trunk/test/Analysis/ScalarEvolution/pr34538.ll (added)
>> +++ llvm/trunk/test/Analysis/ScalarEvolution/pr34538.ll Tue Oct 17
>> 18:36:16 2017
>> @@ -0,0 +1,19 @@
>> +; RUN: opt -S -scalar-evolution -loop-deletion -simplifycfg -analyze <
>> %s | FileCheck %s --check-prefix=CHECK-ANALYSIS
>> +
>> +define i32 @foo() local_unnamed_addr #0 {
>> +; CHECK-ANALYSIS: Loop %do.body: backedge-taken count is 10000
>> +; CHECK-ANALYSIS: Loop %do.body: max backedge-taken count is 10000
>> +; CHECK-ANALYSIS: Loop %do.body: Predicated backedge-taken count is 10000
>> +entry:
>> + br label %do.body
>> +
>> +do.body: ; preds = %do.body,
>> %entry
>> + %start.0 = phi i32 [ 0, %entry ], [ %inc.start.0, %do.body ]
>> + %cmp = icmp slt i32 %start.0, 10000
>> + %inc = zext i1 %cmp to i32
>> + %inc.start.0 = add nsw i32 %start.0, %inc
>> + br i1 %cmp, label %do.body, label %do.end
>> +
>> +do.end: ; preds = %do.body
>> + ret i32 0
>> +}
>>
>>
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