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[InstCombine] canonicalize constant-minus-boolean to select-of-constants 

This restores the half of:
https://reviews.llvm.org/rL75531
that was reverted at:
https://reviews.llvm.org/rL159230

For the x86 case mentioned there, we now produce:
leal 1(%rdi), %eax
subl %esi, %eax

We have target hooks to invert this in DAGCombiner (and x86 is enabled) with:
https://reviews.llvm.org/rL296977
https://reviews.llvm.org/rL311731

AArch64 and possibly other targets would probably benefit from enabling those hooks too. 
See PR30327:
https://bugs.llvm.org/show_bug.cgi?id=30327#c2

Differential Revision: https://reviews.llvm.org/D40612

llvm-svn: 319964
This commit is contained in:
Sanjay Patel 2017-12-06 21:22:57 +00:00
parent e363d2cebb
commit b6404a8ca6
2 changed files with 9 additions and 7 deletions
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7
llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
View File

@ -1520,8 +1520,13 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) {
return BinaryOperator::CreateNot(Op1);
if (Constant *C = dyn_cast<Constant>(Op0)) {
Value *X;
// C - zext(bool) -> bool ? C - 1 : C
if (match(Op1, m_ZExt(m_Value(X))) &&
X->getType()->getScalarSizeInBits() == 1)
return SelectInst::Create(X, SubOne(C), C);
// C - ~X == X + (1+C)
Value *X = nullptr;
if (match(Op1, m_Not(m_Value(X))))
return BinaryOperator::CreateAdd(X, AddOne(C));

9
llvm/test/Transforms/InstCombine/zext-bool-add-sub.ll
View File

@ -20,8 +20,7 @@ define i32 @a(i1 zeroext %x, i1 zeroext %y) {
define i32 @zextsub(i1 %x) {
; CHECK-LABEL: @zextsub(
; CHECK-NEXT: [[ZEXT:%.*]] = zext i1 %x to i32
; CHECK-NEXT: [[SUB:%.*]] = sub nsw i32 11, [[ZEXT]]
; CHECK-NEXT: [[SUB:%.*]] = select i1 %x, i32 10, i32 11
; CHECK-NEXT: ret i32 [[SUB]]
;
%zext = zext i1 %x to i32
@ -31,8 +30,7 @@ define i32 @zextsub(i1 %x) {
define <2 x i32> @zextsub_splat(<2 x i1> %x) {
; CHECK-LABEL: @zextsub_splat(
; CHECK-NEXT: [[ZEXT:%.*]] = zext <2 x i1> %x to <2 x i32>
; CHECK-NEXT: [[SUB:%.*]] = sub nsw <2 x i32> <i32 42, i32 42>, [[ZEXT]]
; CHECK-NEXT: [[SUB:%.*]] = select <2 x i1> %x, <2 x i32> <i32 41, i32 41>, <2 x i32> <i32 42, i32 42>
; CHECK-NEXT: ret <2 x i32> [[SUB]]
;
%zext = zext <2 x i1> %x to <2 x i32>
@ -42,8 +40,7 @@ define <2 x i32> @zextsub_splat(<2 x i1> %x) {
define <2 x i32> @zextsub_vec(<2 x i1> %x) {
; CHECK-LABEL: @zextsub_vec(
; CHECK-NEXT: [[ZEXT:%.*]] = zext <2 x i1> %x to <2 x i32>
; CHECK-NEXT: [[SUB:%.*]] = sub nsw <2 x i32> <i32 11, i32 42>, [[ZEXT]]
; CHECK-NEXT: [[SUB:%.*]] = select <2 x i1> %x, <2 x i32> <i32 10, i32 41>, <2 x i32> <i32 11, i32 42>
; CHECK-NEXT: ret <2 x i32> [[SUB]]
;
%zext = zext <2 x i1> %x to <2 x i32>