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[InstCombine] try to fold 'sub' to 'not' 

https://rise4fun.com/Alive/jDd

Patterns with add/sub combos can be improved using
'not' ops. This is better for analysis and may lead
to follow-on transforms because 'xor' and 'add' are 
commutative/associative. It can also help codegen.  

llvm-svn: 338200
This commit is contained in:
Sanjay Patel 2018-07-28 16:48:44 +00:00
parent 376051820d
commit 818b253d3a
2 changed files with 11 additions and 5 deletions
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8
llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
View File

@ -926,7 +926,13 @@ Instruction *InstCombiner::foldAddWithConstant(BinaryOperator &Add) {
if (Instruction *NV = foldBinOpIntoSelectOrPhi(Add))
return NV;
Value *X;
Value *X, *Y;
// add (sub X, Y), -1 --> add (not Y), X
if (match(Op0, m_OneUse(m_Sub(m_Value(X), m_Value(Y)))) &&
match(Op1, m_AllOnes()))
return BinaryOperator::CreateAdd(Builder.CreateNot(Y), X);
// zext(bool) + C -> bool ? C + 1 : C
if (match(Op0, m_ZExt(m_Value(X))) &&
X->getType()->getScalarSizeInBits() == 1)

8
llvm/test/Transforms/InstCombine/sub-not.ll
View File

@ -40,8 +40,8 @@ define <2 x i8> @sub_not_vec(<2 x i8> %x, <2 x i8> %y) {
define i8 @dec_sub(i8 %x, i8 %y) {
; CHECK-LABEL: @dec_sub(
; CHECK-NEXT: [[S:%.*]] = sub i8 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[R:%.*]] = add i8 [[S]], -1
; CHECK-NEXT: [[TMP1:%.*]] = xor i8 [[Y:%.*]], -1
; CHECK-NEXT: [[R:%.*]] = add i8 [[TMP1]], [[X:%.*]]
; CHECK-NEXT: ret i8 [[R]]
;
%s = sub i8 %x, %y
@ -64,8 +64,8 @@ define i8 @dec_sub_extra_use(i8 %x, i8 %y) {
define <2 x i8> @dec_sub_vec(<2 x i8> %x, <2 x i8> %y) {
; CHECK-LABEL: @dec_sub_vec(
; CHECK-NEXT: [[S:%.*]] = sub <2 x i8> [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[R:%.*]] = add <2 x i8> [[S]], <i8 -1, i8 undef>
; CHECK-NEXT: [[TMP1:%.*]] = xor <2 x i8> [[Y:%.*]], <i8 -1, i8 -1>
; CHECK-NEXT: [[R:%.*]] = add <2 x i8> [[TMP1]], [[X:%.*]]
; CHECK-NEXT: ret <2 x i8> [[R]]
;
%s = sub <2 x i8> %x, %y