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[Reassociate] Better preserve NSW/NUW flags.
Part of PR12985. Phabricator Revision: http://reviews.llvm.org/D6172 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221555 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -1031,8 +1031,19 @@ static BinaryOperator *ConvertShiftToMul(Instruction *Shl) {
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BinaryOperator::CreateMul(Shl->getOperand(0), MulCst, "", Shl);
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Shl->setOperand(0, UndefValue::get(Shl->getType())); // Drop use of op.
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Mul->takeName(Shl);
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// Everyone now refers to the mul instruction.
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Shl->replaceAllUsesWith(Mul);
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Mul->setDebugLoc(Shl->getDebugLoc());
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// We can safely preserve the nuw flag in all cases. It's also safe to turn a
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// nuw nsw shl into a nuw nsw mul. However, nsw in isolation requires special
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// handling.
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bool NSW = cast<BinaryOperator>(Shl)->hasNoSignedWrap();
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bool NUW = cast<BinaryOperator>(Shl)->hasNoUnsignedWrap();
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if (NSW && NUW)
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Mul->setHasNoSignedWrap(true);
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Mul->setHasNoUnsignedWrap(NUW);
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return Mul;
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}
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34
test/Transforms/Reassociate/wrap-flags.ll
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34
test/Transforms/Reassociate/wrap-flags.ll
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@ -0,0 +1,34 @@
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; RUN: opt < %s -reassociate -dce -S | FileCheck %s
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; PR12985
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; Verify the nsw flags are preserved when converting shl to mul.
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; CHECK-LABEL: @shl_to_mul_nsw(
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; CHECK: %mul = mul i32 %i, -2147483648
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; CHECK: %mul2 = add i32 %mul, 1
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define i32 @shl_to_mul_nsw(i32 %i) {
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entry:
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%mul = shl nsw i32 %i, 31
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%mul2 = add i32 %mul, 1
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ret i32 %mul2
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}
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; CHECK-LABEL: @shl_to_mul_nuw(
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; CHECK: %mul = mul nuw i32 %i, 4
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; CHECK: %mul2 = add i32 %mul, 1
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define i32 @shl_to_mul_nuw(i32 %i) {
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entry:
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%mul = shl nuw i32 %i, 2
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%mul2 = add i32 %mul, 1
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ret i32 %mul2
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}
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; CHECK-LABEL: @shl_to_mul_nuw_nsw(
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; CHECK: %mul = mul nuw nsw i32 %i, 4
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; CHECK: %mul2 = add i32 %mul, 1
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define i32 @shl_to_mul_nuw_nsw(i32 %i) {
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entry:
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%mul = shl nuw nsw i32 %i, 2
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%mul2 = add i32 %mul, 1
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ret i32 %mul2
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}
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