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[Reassociate] Better preserve NSW/NUW flags.

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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
This commit is contained in:
Chad Rosier 2014-11-07 22:12:57 +00:00
parent 6faf6b1833
commit bcdc4769f4
2 changed files with 45 additions and 0 deletions
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11
lib/Transforms/Scalar/Reassociate.cpp
View File

@ -1031,8 +1031,19 @@ static BinaryOperator *ConvertShiftToMul(Instruction *Shl) {
BinaryOperator::CreateMul(Shl->getOperand(0), MulCst, "", Shl);
Shl->setOperand(0, UndefValue::get(Shl->getType())); // Drop use of op.
Mul->takeName(Shl);
// Everyone now refers to the mul instruction.
Shl->replaceAllUsesWith(Mul);
Mul->setDebugLoc(Shl->getDebugLoc());
// We can safely preserve the nuw flag in all cases. It's also safe to turn a
// nuw nsw shl into a nuw nsw mul. However, nsw in isolation requires special
// handling.
bool NSW = cast<BinaryOperator>(Shl)->hasNoSignedWrap();
bool NUW = cast<BinaryOperator>(Shl)->hasNoUnsignedWrap();
if (NSW && NUW)
Mul->setHasNoSignedWrap(true);
Mul->setHasNoUnsignedWrap(NUW);
return Mul;
}

34
test/Transforms/Reassociate/wrap-flags.ll Normal file
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@ -0,0 +1,34 @@
; RUN: opt < %s -reassociate -dce -S | FileCheck %s
; PR12985
; Verify the nsw flags are preserved when converting shl to mul.
; CHECK-LABEL: @shl_to_mul_nsw(
; CHECK: %mul = mul i32 %i, -2147483648
; CHECK: %mul2 = add i32 %mul, 1
define i32 @shl_to_mul_nsw(i32 %i) {
entry:
%mul = shl nsw i32 %i, 31
%mul2 = add i32 %mul, 1
ret i32 %mul2
}
; CHECK-LABEL: @shl_to_mul_nuw(
; CHECK: %mul = mul nuw i32 %i, 4
; CHECK: %mul2 = add i32 %mul, 1
define i32 @shl_to_mul_nuw(i32 %i) {
entry:
%mul = shl nuw i32 %i, 2
%mul2 = add i32 %mul, 1
ret i32 %mul2
}
; CHECK-LABEL: @shl_to_mul_nuw_nsw(
; CHECK: %mul = mul nuw nsw i32 %i, 4
; CHECK: %mul2 = add i32 %mul, 1
define i32 @shl_to_mul_nuw_nsw(i32 %i) {
entry:
%mul = shl nuw nsw i32 %i, 2
%mul2 = add i32 %mul, 1
ret i32 %mul2
}