[llvm] r230280 - Bugfix: SCEVExpander incorrectly marks increment operations as no-wrap
H.J. Lu
hjl.tools at gmail.com
Tue Feb 24 05:52:41 PST 2015
It caused:
http://llvm.org/bugs/show_bug.cgi?id=22674
On Mon, Feb 23, 2015 at 3:23 PM, Sanjoy Das
<sanjoy at playingwithpointers.com> wrote:
> Author: sanjoy
> Date: Mon Feb 23 17:22:58 2015
> New Revision: 230280
>
> URL: http://llvm.org/viewvc/llvm-project?rev=230280&view=rev
> Log:
> Bugfix: SCEVExpander incorrectly marks increment operations as no-wrap
>
> When emitting the increment operation, SCEVExpander marks the
> operation as nuw or nsw based on the flags on the preincrement SCEV.
> This is incorrect because, for instance, it is possible that {-6,+,1}
> is <nuw> while {-6,+,1}+1 = {-5,+,1} is not.
>
> This change teaches SCEV to mark the increment as nuw/nsw only if it
> can explicitly prove that the increment operation won't overflow.
>
> Apart from the attached test case, another (more realistic) manifestation
> of the bug can be seen in Transforms/IndVarSimplify/pr20680.ll.
>
> NOTE: this change was landed with an incorrect commit message in
> rL230275 and was reverted for that reason in rL230279. This commit
> message is the correct one.
>
> Differential Revision: http://reviews.llvm.org/D7778
>
>
> Added:
> llvm/trunk/test/Analysis/ScalarEvolution/scev-expander-incorrect-nowrap.ll
> Modified:
> llvm/trunk/lib/Analysis/ScalarEvolutionExpander.cpp
> llvm/trunk/test/Analysis/ScalarEvolution/zext-signed-addrec.ll
> llvm/trunk/test/CodeGen/AArch64/arm64-scaled_iv.ll
> llvm/trunk/test/CodeGen/X86/avoid_complex_am.ll
> llvm/trunk/test/Transforms/IndVarSimplify/overflowcheck.ll
> llvm/trunk/test/Transforms/IndVarSimplify/pr20680.ll
> llvm/trunk/test/Transforms/LoopStrengthReduce/count-to-zero.ll
> llvm/trunk/test/Transforms/LoopStrengthReduce/uglygep.ll
>
> Modified: llvm/trunk/lib/Analysis/ScalarEvolutionExpander.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolutionExpander.cpp?rev=230280&r1=230279&r2=230280&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Analysis/ScalarEvolutionExpander.cpp (original)
> +++ llvm/trunk/lib/Analysis/ScalarEvolutionExpander.cpp Mon Feb 23 17:22:58 2015
> @@ -1063,6 +1063,34 @@ static bool canBeCheaplyTransformed(Scal
> return false;
> }
>
> +static bool IsIncrementNSW(ScalarEvolution &SE, const SCEVAddRecExpr *AR) {
> + if (!isa<IntegerType>(AR->getType()))
> + return false;
> +
> + unsigned BitWidth = cast<IntegerType>(AR->getType())->getBitWidth();
> + Type *WideTy = IntegerType::get(AR->getType()->getContext(), BitWidth * 2);
> + const SCEV *Step = AR->getStepRecurrence(SE);
> + const SCEV *OpAfterExtend = SE.getAddExpr(SE.getSignExtendExpr(Step, WideTy),
> + SE.getSignExtendExpr(AR, WideTy));
> + const SCEV *ExtendAfterOp =
> + SE.getSignExtendExpr(SE.getAddExpr(AR, Step), WideTy);
> + return ExtendAfterOp == OpAfterExtend;
> +}
> +
> +static bool IsIncrementNUW(ScalarEvolution &SE, const SCEVAddRecExpr *AR) {
> + if (!isa<IntegerType>(AR->getType()))
> + return false;
> +
> + unsigned BitWidth = cast<IntegerType>(AR->getType())->getBitWidth();
> + Type *WideTy = IntegerType::get(AR->getType()->getContext(), BitWidth * 2);
> + const SCEV *Step = AR->getStepRecurrence(SE);
> + const SCEV *OpAfterExtend = SE.getAddExpr(SE.getZeroExtendExpr(Step, WideTy),
> + SE.getZeroExtendExpr(AR, WideTy));
> + const SCEV *ExtendAfterOp =
> + SE.getZeroExtendExpr(SE.getAddExpr(AR, Step), WideTy);
> + return ExtendAfterOp == OpAfterExtend;
> +}
> +
> /// getAddRecExprPHILiterally - Helper for expandAddRecExprLiterally. Expand
> /// the base addrec, which is the addrec without any non-loop-dominating
> /// values, and return the PHI.
> @@ -1213,10 +1241,11 @@ SCEVExpander::getAddRecExprPHILiterally(
> IVIncInsertPos : Pred->getTerminator();
> Builder.SetInsertPoint(InsertPos);
> Value *IncV = expandIVInc(PN, StepV, L, ExpandTy, IntTy, useSubtract);
> +
> if (isa<OverflowingBinaryOperator>(IncV)) {
> - if (Normalized->getNoWrapFlags(SCEV::FlagNUW))
> + if (IsIncrementNUW(SE, Normalized))
> cast<BinaryOperator>(IncV)->setHasNoUnsignedWrap();
> - if (Normalized->getNoWrapFlags(SCEV::FlagNSW))
> + if (IsIncrementNSW(SE, Normalized))
> cast<BinaryOperator>(IncV)->setHasNoSignedWrap();
> }
> PN->addIncoming(IncV, Pred);
>
> Added: llvm/trunk/test/Analysis/ScalarEvolution/scev-expander-incorrect-nowrap.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/scev-expander-incorrect-nowrap.ll?rev=230280&view=auto
> ==============================================================================
> --- llvm/trunk/test/Analysis/ScalarEvolution/scev-expander-incorrect-nowrap.ll (added)
> +++ llvm/trunk/test/Analysis/ScalarEvolution/scev-expander-incorrect-nowrap.ll Mon Feb 23 17:22:58 2015
> @@ -0,0 +1,30 @@
> +; RUN: opt -indvars -S < %s | FileCheck %s
> +
> +declare void @use(i32)
> +declare void @use.i8(i8)
> +
> +define void @f() {
> +; CHECK-LABEL: @f
> + entry:
> + br label %loop
> +
> + loop:
> +; The only use for idx.mirror is to induce an nuw for %idx. It does
> +; not induce an nuw for %idx.inc
> + %idx.mirror = phi i8 [ -6, %entry ], [ %idx.mirror.inc, %loop ]
> + %idx = phi i8 [ -5, %entry ], [ %idx.inc, %loop ]
> +
> + %idx.sext = sext i8 %idx to i32
> + call void @use(i32 %idx.sext)
> +
> + %idx.mirror.inc = add nuw i8 %idx.mirror, 1
> + call void @use.i8(i8 %idx.mirror.inc)
> +
> + %idx.inc = add i8 %idx, 1
> +; CHECK-NOT: %indvars.iv.next = add nuw nsw i32 %indvars.iv, 1
> + %cmp = icmp ugt i8 %idx.inc, 0
> + br i1 %cmp, label %loop, label %exit
> +
> + exit:
> + ret void
> +}
>
> Modified: llvm/trunk/test/Analysis/ScalarEvolution/zext-signed-addrec.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/zext-signed-addrec.ll?rev=230280&r1=230279&r2=230280&view=diff
> ==============================================================================
> --- llvm/trunk/test/Analysis/ScalarEvolution/zext-signed-addrec.ll (original)
> +++ llvm/trunk/test/Analysis/ScalarEvolution/zext-signed-addrec.ll Mon Feb 23 17:22:58 2015
> @@ -43,7 +43,7 @@ if.end:
> %shl = and i32 %conv7, 510
> store i32 %shl, i32* @c, align 4
>
> -; CHECK: %lsr.iv.next = add i32 %lsr.iv, -258
> +; CHECK: %lsr.iv.next = add nsw i32 %lsr.iv, -258
> %dec = add i8 %2, -1
>
> %cmp2 = icmp sgt i8 %dec, -1
>
> Modified: llvm/trunk/test/CodeGen/AArch64/arm64-scaled_iv.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/AArch64/arm64-scaled_iv.ll?rev=230280&r1=230279&r2=230280&view=diff
> ==============================================================================
> --- llvm/trunk/test/CodeGen/AArch64/arm64-scaled_iv.ll (original)
> +++ llvm/trunk/test/CodeGen/AArch64/arm64-scaled_iv.ll Mon Feb 23 17:22:58 2015
> @@ -20,7 +20,7 @@ for.body:
> %arrayidx = getelementptr inbounds double* %b, i64 %tmp
> %tmp1 = load double* %arrayidx, align 8
> ; The induction variable should carry the scaling factor: 1 * 8 = 8.
> -; CHECK: [[IVNEXT]] = add nuw i64 [[IV]], 8
> +; CHECK: [[IVNEXT]] = add nuw nsw i64 [[IV]], 8
> %indvars.iv.next = add i64 %indvars.iv, 1
> %arrayidx2 = getelementptr inbounds double* %c, i64 %indvars.iv.next
> %tmp2 = load double* %arrayidx2, align 8
>
> Modified: llvm/trunk/test/CodeGen/X86/avoid_complex_am.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/avoid_complex_am.ll?rev=230280&r1=230279&r2=230280&view=diff
> ==============================================================================
> --- llvm/trunk/test/CodeGen/X86/avoid_complex_am.ll (original)
> +++ llvm/trunk/test/CodeGen/X86/avoid_complex_am.ll Mon Feb 23 17:22:58 2015
> @@ -22,7 +22,7 @@ for.body:
> %arrayidx = getelementptr inbounds double* %b, i64 %tmp
> %tmp1 = load double* %arrayidx, align 8
> ; The induction variable should carry the scaling factor: 1.
> -; CHECK: [[IVNEXT]] = add nuw i64 [[IV]], 1
> +; CHECK: [[IVNEXT]] = add nuw nsw i64 [[IV]], 1
> %indvars.iv.next = add i64 %indvars.iv, 1
> %arrayidx2 = getelementptr inbounds double* %c, i64 %indvars.iv.next
> %tmp2 = load double* %arrayidx2, align 8
>
> Modified: llvm/trunk/test/Transforms/IndVarSimplify/overflowcheck.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/IndVarSimplify/overflowcheck.ll?rev=230280&r1=230279&r2=230280&view=diff
> ==============================================================================
> --- llvm/trunk/test/Transforms/IndVarSimplify/overflowcheck.ll (original)
> +++ llvm/trunk/test/Transforms/IndVarSimplify/overflowcheck.ll Mon Feb 23 17:22:58 2015
> @@ -9,7 +9,7 @@ target triple = "x86_64-apple-macosx"
> ; CHECK: @llvm.sadd.with.overflow
> ; CHECK-LABEL: loop2:
> ; CHECK-NOT: extractvalue
> -; CHECK: add nuw nsw
> +; CHECK: add nuw
> ; CHECK: @llvm.sadd.with.overflow
> ; CHECK-LABEL: loop3:
> ; CHECK-NOT: extractvalue
>
> Modified: llvm/trunk/test/Transforms/IndVarSimplify/pr20680.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/IndVarSimplify/pr20680.ll?rev=230280&r1=230279&r2=230280&view=diff
> ==============================================================================
> --- llvm/trunk/test/Transforms/IndVarSimplify/pr20680.ll (original)
> +++ llvm/trunk/test/Transforms/IndVarSimplify/pr20680.ll Mon Feb 23 17:22:58 2015
> @@ -204,8 +204,8 @@ for.cond2.for.inc13_crit_edge:
> br label %for.inc13
>
> ; CHECK: [[for_inc13]]:
> -; CHECK-NEXT: %[[indvars_iv_next]] = add nuw nsw i32 %[[indvars_iv]], 1
> -; CHECK-NEXT: %[[exitcond4:.*]] = icmp ne i32 %[[indvars_iv]], -1
> +; CHECK-NEXT: %[[indvars_iv_next]] = add nsw i32 %[[indvars_iv]], 1
> +; CHECK-NEXT: %[[exitcond4:.*]] = icmp ne i32 %[[indvars_iv_next]], 0
> ; CHECK-NEXT: br i1 %[[exitcond4]], label %[[for_cond2_preheader]], label %[[for_end15:.*]]
> for.inc13: ; preds = %for.cond2.for.inc13_crit_edge, %for.cond2.preheader
> %inc14 = add i8 %storemerge15, 1
>
> Modified: llvm/trunk/test/Transforms/LoopStrengthReduce/count-to-zero.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopStrengthReduce/count-to-zero.ll?rev=230280&r1=230279&r2=230280&view=diff
> ==============================================================================
> --- llvm/trunk/test/Transforms/LoopStrengthReduce/count-to-zero.ll (original)
> +++ llvm/trunk/test/Transforms/LoopStrengthReduce/count-to-zero.ll Mon Feb 23 17:22:58 2015
> @@ -19,7 +19,7 @@ bb3:
> %tmp4 = add i32 %c_addr.1, -1 ; <i32> [#uses=1]
> %c_addr.1.be = select i1 %tmp2, i32 %tmp3, i32 %tmp4 ; <i32> [#uses=1]
> %indvar.next = add i32 %indvar, 1 ; <i32> [#uses=1]
> -; CHECK: add i32 %lsr.iv, -1
> +; CHECK: add nsw i32 %lsr.iv, -1
> br label %bb6
>
> bb6: ; preds = %bb3, %entry
>
> Modified: llvm/trunk/test/Transforms/LoopStrengthReduce/uglygep.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopStrengthReduce/uglygep.ll?rev=230280&r1=230279&r2=230280&view=diff
> ==============================================================================
> --- llvm/trunk/test/Transforms/LoopStrengthReduce/uglygep.ll (original)
> +++ llvm/trunk/test/Transforms/LoopStrengthReduce/uglygep.ll Mon Feb 23 17:22:58 2015
> @@ -59,7 +59,7 @@ bb:
> ; CHECK: loop0:
> ; Induction variable is initialized to -2.
> ; CHECK-NEXT: [[PHIIV:%[^ ]+]] = phi i32 [ [[IVNEXT:%[^ ]+]], %loop0 ], [ -2, %bb ]
> -; CHECK-NEXT: [[IVNEXT]] = add i32 [[PHIIV]], 1
> +; CHECK-NEXT: [[IVNEXT]] = add nuw nsw i32 [[PHIIV]], 1
> ; CHECK-NEXT: br i1 false, label %loop0, label %bb0
> loop0: ; preds = %loop0, %bb
> %i0 = phi i32 [ %i0.next, %loop0 ], [ 0, %bb ] ; <i32> [#uses=2]
>
>
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--
H.J.
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