[llvm] r316054 - [ScalarEvolution] Handling for ICmp occuring in the evolution chain.
Sanjoy Das via llvm-commits
llvm-commits at lists.llvm.org
Tue Oct 17 21:52:36 PDT 2017
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>(Accum)->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/Transforms/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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