[llvm] r310117 - [SCEV] Preserve NSW information for sext(subtract).
Amara Emerson via llvm-commits
llvm-commits at lists.llvm.org
Fri Aug 4 13:19:46 PDT 2017
Author: aemerson
Date: Fri Aug 4 13:19:46 2017
New Revision: 310117
URL: http://llvm.org/viewvc/llvm-project?rev=310117&view=rev
Log:
[SCEV] Preserve NSW information for sext(subtract).
Pushes the sext onto the operands of a Sub if NSW is present.
Also adds support for propagating the nowrap flags of the
llvm.ssub.with.overflow intrinsic during analysis.
Differential Revision: https://reviews.llvm.org/D35256
Modified:
llvm/trunk/lib/Analysis/ScalarEvolution.cpp
llvm/trunk/test/Analysis/ScalarEvolution/flags-from-poison.ll
llvm/trunk/test/Transforms/LoopStrengthReduce/sext-ind-var.ll
Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=310117&r1=310116&r2=310117&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Fri Aug 4 13:19:46 2017
@@ -4168,10 +4168,21 @@ static Optional<BinaryOp> MatchBinaryOp(
}
case Intrinsic::ssub_with_overflow:
- case Intrinsic::usub_with_overflow:
- return BinaryOp(Instruction::Sub, CI->getArgOperand(0),
- CI->getArgOperand(1));
-
+ case Intrinsic::usub_with_overflow: {
+ if (!isOverflowIntrinsicNoWrap(cast<IntrinsicInst>(CI), DT))
+ return BinaryOp(Instruction::Sub, CI->getArgOperand(0),
+ CI->getArgOperand(1));
+
+ // The same reasoning as sadd/uadd above.
+ if (F->getIntrinsicID() == Intrinsic::ssub_with_overflow)
+ return BinaryOp(Instruction::Sub, CI->getArgOperand(0),
+ CI->getArgOperand(1), /* IsNSW = */ true,
+ /* IsNUW = */ false);
+ else
+ return BinaryOp(Instruction::Sub, CI->getArgOperand(0),
+ CI->getArgOperand(1), /* IsNSW = */ false,
+ /* IsNUW = */ true);
+ }
case Intrinsic::smul_with_overflow:
case Intrinsic::umul_with_overflow:
return BinaryOp(Instruction::Mul, CI->getArgOperand(0),
@@ -5952,6 +5963,21 @@ const SCEV *ScalarEvolution::createSCEV(
return getZeroExtendExpr(getSCEV(U->getOperand(0)), U->getType());
case Instruction::SExt:
+ if (auto BO = MatchBinaryOp(U->getOperand(0), DT)) {
+ // The NSW flag of a subtract does not always survive the conversion to
+ // A + (-1)*B. By pushing sign extension onto its operands we are much
+ // more likely to preserve NSW and allow later AddRec optimisations.
+ //
+ // NOTE: This is effectively duplicating this logic from getSignExtend:
+ // sext((A + B + ...)<nsw>) --> (sext(A) + sext(B) + ...)<nsw>
+ // but by that point the NSW information has potentially been lost.
+ if (BO->Opcode == Instruction::Sub && BO->IsNSW) {
+ Type *Ty = U->getType();
+ auto *V1 = getSignExtendExpr(getSCEV(BO->LHS), Ty);
+ auto *V2 = getSignExtendExpr(getSCEV(BO->RHS), Ty);
+ return getMinusSCEV(V1, V2, SCEV::FlagNSW);
+ }
+ }
return getSignExtendExpr(getSCEV(U->getOperand(0)), U->getType());
case Instruction::BitCast:
Modified: llvm/trunk/test/Analysis/ScalarEvolution/flags-from-poison.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/flags-from-poison.ll?rev=310117&r1=310116&r2=310117&view=diff
==============================================================================
--- llvm/trunk/test/Analysis/ScalarEvolution/flags-from-poison.ll (original)
+++ llvm/trunk/test/Analysis/ScalarEvolution/flags-from-poison.ll Fri Aug 4 13:19:46 2017
@@ -609,11 +609,45 @@ loop:
%index32 = sub nsw i32 %i, %sub
; CHECK: %index64 =
-; CHECK: --> {(sext i32 (-1 * %sub) to i64),+,1}<nsw>
+; CHECK: --> {(-1 * (sext i32 %sub to i64))<nsw>,+,1}<nsw
%index64 = sext i32 %index32 to i64
%ptr = getelementptr inbounds float, float* %input, i64 %index64
%nexti = add nsw i32 %i, 1
+ %f = load float, float* %ptr, align 4
+ %exitcond = icmp eq i32 %nexti, %numIterations
+ br i1 %exitcond, label %exit, label %loop
+exit:
+ ret void
+}
+
+; Example checking that a sext is pushed onto a sub's operands if the sub is an
+; overflow intrinsic.
+define void @test-sext-sub(float* %input, i32 %sub, i32 %numIterations) {
+; CHECK-LABEL: @test-sext-sub
+entry:
+ br label %loop
+loop:
+ %i = phi i32 [ %nexti, %cont ], [ 0, %entry ]
+
+; CHECK: %val = extractvalue { i32, i1 } %ssub, 0
+; CHECK: --> {(-1 * %sub),+,1}<nw>
+ %ssub = tail call { i32, i1 } @llvm.ssub.with.overflow.i32(i32 %i, i32 %sub)
+ %val = extractvalue { i32, i1 } %ssub, 0
+ %ovfl = extractvalue { i32, i1 } %ssub, 1
+ br i1 %ovfl, label %trap, label %cont
+
+trap:
+ tail call void @llvm.trap()
+ unreachable
+
+cont:
+; CHECK: %index64 =
+; CHECK: --> {(-1 * (sext i32 %sub to i64))<nsw>,+,1}<nsw
+ %index64 = sext i32 %val to i64
+
+ %ptr = getelementptr inbounds float, float* %input, i64 %index64
+ %nexti = add nsw i32 %i, 1
%f = load float, float* %ptr, align 4
%exitcond = icmp eq i32 %nexti, %numIterations
br i1 %exitcond, label %exit, label %loop
Modified: llvm/trunk/test/Transforms/LoopStrengthReduce/sext-ind-var.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopStrengthReduce/sext-ind-var.ll?rev=310117&r1=310116&r2=310117&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LoopStrengthReduce/sext-ind-var.ll (original)
+++ llvm/trunk/test/Transforms/LoopStrengthReduce/sext-ind-var.ll Fri Aug 4 13:19:46 2017
@@ -47,8 +47,7 @@ exit:
;
define float @testsub(float* %input, i32 %offset, i32 %numIterations) {
; CHECK-LABEL: @testsub
-; CHECK: sub i32 0, %offset
-; CHECK: sext i32
+; CHECK: sext i32 %offset to i64
; CHECK: loop:
; CHECK-DAG: phi float*
; CHECK-DAG: phi i32
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