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[InstSimplify] add nsw/nuw (xor X, signbit), signbit --> X

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The change to InstCombine in:
https://reviews.llvm.org/D29729
...exposes this missing fold in InstSimplify, so adding this
first to avoid a regression.

llvm-svn: 295573
This commit is contained in:
Sanjay Patel 2017-02-18 21:59:09 +00:00
parent dbc786ab1d
commit ab7638b75f
3 changed files with 16 additions and 8 deletions
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12
lib/Analysis/InstructionSimplify.cpp
View File

@ -557,9 +557,19 @@ static Value *SimplifyAddInst(Value *Op0, Value *Op1, bool isNSW, bool isNUW,
return Y;
// X + ~X -> -1 since ~X = -X-1
Type *Ty = Op0->getType();
if (match(Op0, m_Not(m_Specific(Op1))) ||
match(Op1, m_Not(m_Specific(Op0))))
return Constant::getAllOnesValue(Op0->getType());
return Constant::getAllOnesValue(Ty);
// add nsw/nuw (xor Y, signbit), signbit --> Y
// The no-wrapping add guarantees that the top bit will be set by the add.
// Therefore, the xor must be clearing the already set sign bit of Y.
Constant *SignBit =
ConstantInt::get(Ty, APInt::getSignBit(Ty->getScalarSizeInBits()));
if ((isNSW || isNUW) && match(Op1, m_Specific(SignBit)) &&
match(Op0, m_Xor(m_Value(Y), m_Specific(SignBit))))
return Y;
/// i1 add -> xor.
if (MaxRecurse && Op0->getType()->isIntegerTy(1))

4
test/Transforms/InstCombine/add.ll
View File

@ -244,7 +244,9 @@ define i32 @test19(i1 %C) {
ret i32 %V
}
; Add of sign bit -> xor of sign bit.
; This is an InstSimplify fold, but test it here to make sure that
; InstCombine does not prevent the fold.
; With NSW, add of sign bit -> or of sign bit.
define i32 @test20(i32 %x) {
; CHECK-LABEL: @test20(

8
test/Transforms/InstSimplify/AndOrXor.ll
View File

@ -5,9 +5,7 @@
define <2 x i32> @add_nsw_signbit(<2 x i32> %x) {
; CHECK-LABEL: @add_nsw_signbit(
; CHECK-NEXT: [[Y:%.*]] = xor <2 x i32> %x, <i32 -2147483648, i32 -2147483648>
; CHECK-NEXT: [[Z:%.*]] = add nsw <2 x i32> [[Y]], <i32 -2147483648, i32 -2147483648>
; CHECK-NEXT: ret <2 x i32> [[Z]]
; CHECK-NEXT: ret <2 x i32> %x
;
%y = xor <2 x i32> %x, <i32 -2147483648, i32 -2147483648>
%z = add nsw <2 x i32> %y, <i32 -2147483648, i32 -2147483648>
@ -18,9 +16,7 @@ define <2 x i32> @add_nsw_signbit(<2 x i32> %x) {
define <2 x i5> @add_nuw_signbit(<2 x i5> %x) {
; CHECK-LABEL: @add_nuw_signbit(
; CHECK-NEXT: [[Y:%.*]] = xor <2 x i5> %x, <i5 -16, i5 -16>
; CHECK-NEXT: [[Z:%.*]] = add nuw <2 x i5> [[Y]], <i5 -16, i5 -16>
; CHECK-NEXT: ret <2 x i5> [[Z]]
; CHECK-NEXT: ret <2 x i5> %x
;
%y = xor <2 x i5> %x, <i5 -16, i5 -16>
%z = add nuw <2 x i5> %y, <i5 -16, i5 -16>