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[InstCombine] Y - ~X --> X + Y + 1 fold (PR42457) 

Summary:
I *think* we'd want this new variant, because we obviously
have better handling for `add` as compared to `sub`/`not`.

https://rise4fun.com/Alive/WMn

Fixes [[ https://bugs.llvm.org/show_bug.cgi?id=42457 | PR42457 ]]

Reviewers: spatel, nikic, huihuiz, efriedma

Reviewed By: spatel

Subscribers: RKSimon, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D63992

llvm-svn: 365011
This commit is contained in:
Roman Lebedev 2019-07-03 09:41:50 +00:00
parent c4b83a6054
commit 9f0c83902d
2 changed files with 14 additions and 7 deletions
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6
llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
View File

@ -1580,6 +1580,12 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) {
if (match(Op1, m_OneUse(m_Add(m_Value(X), m_One()))))
return BinaryOperator::CreateAdd(Builder.CreateNot(X), Op0);
// Y - ~X --> (X + 1) + Y
if (match(Op1, m_OneUse(m_Not(m_Value(X))))) {
return BinaryOperator::CreateAdd(
Builder.CreateAdd(Op0, ConstantInt::get(I.getType(), 1)), X);
}
if (Constant *C = dyn_cast<Constant>(Op0)) {
bool IsNegate = match(C, m_ZeroInt());
Value *X;

15
llvm/test/Transforms/InstCombine/fold-sub-of-not-to-inc-of-add.ll
View File

@ -4,7 +4,8 @@
; Given:
; sub %y, (xor %x, -1)
; Transform it to:
; add (add %x, %y), 1
; add (add %x, 1), %y
; We prefer this form because that is what -reassociate would produce.
;------------------------------------------------------------------------------;
; Scalar tests
@ -12,8 +13,8 @@
define i32 @p0_scalar(i32 %x, i32 %y) {
; CHECK-LABEL: @p0_scalar(
; CHECK-NEXT: [[T0:%.*]] = xor i32 [[X:%.*]], -1
; CHECK-NEXT: [[T1:%.*]] = sub i32 [[Y:%.*]], [[T0]]
; CHECK-NEXT: [[TMP1:%.*]] = add i32 [[Y:%.*]], 1
; CHECK-NEXT: [[T1:%.*]] = add i32 [[TMP1]], [[X:%.*]]
; CHECK-NEXT: ret i32 [[T1]]
;
%t0 = xor i32 %x, -1
@ -27,8 +28,8 @@ define i32 @p0_scalar(i32 %x, i32 %y) {
define <4 x i32> @p1_vector_splat(<4 x i32> %x, <4 x i32> %y) {
; CHECK-LABEL: @p1_vector_splat(
; CHECK-NEXT: [[T0:%.*]] = xor <4 x i32> [[X:%.*]], <i32 -1, i32 -1, i32 -1, i32 -1>
; CHECK-NEXT: [[T1:%.*]] = sub <4 x i32> [[Y:%.*]], [[T0]]
; CHECK-NEXT: [[TMP1:%.*]] = add <4 x i32> [[Y:%.*]], <i32 1, i32 1, i32 1, i32 1>
; CHECK-NEXT: [[T1:%.*]] = add <4 x i32> [[TMP1]], [[X:%.*]]
; CHECK-NEXT: ret <4 x i32> [[T1]]
;
%t0 = xor <4 x i32> %x, <i32 -1, i32 -1, i32 -1, i32 -1>
@ -38,8 +39,8 @@ define <4 x i32> @p1_vector_splat(<4 x i32> %x, <4 x i32> %y) {
define <4 x i32> @p2_vector_undef(<4 x i32> %x, <4 x i32> %y) {
; CHECK-LABEL: @p2_vector_undef(
; CHECK-NEXT: [[T0:%.*]] = xor <4 x i32> [[X:%.*]], <i32 -1, i32 -1, i32 undef, i32 -1>
; CHECK-NEXT: [[T1:%.*]] = sub <4 x i32> [[Y:%.*]], [[T0]]
; CHECK-NEXT: [[TMP1:%.*]] = add <4 x i32> [[Y:%.*]], <i32 1, i32 1, i32 1, i32 1>
; CHECK-NEXT: [[T1:%.*]] = add <4 x i32> [[TMP1]], [[X:%.*]]
; CHECK-NEXT: ret <4 x i32> [[T1]]
;
%t0 = xor <4 x i32> %x, <i32 -1, i32 -1, i32 undef, i32 -1>