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[NFC][InstCombine] '(X & (- Y)) - X' -> '- (X & (Y - 1))' fold (PR44448) 

Name: (X & (- Y)) - X  ->  - (X & (Y - 1))  (PR44448)
  %negy = sub i8 0, %y
  %unbiasedx = and i8 %negy, %x
  %r = sub i8 %unbiasedx, %x
=>
  %ymask = add i8 %y, -1
  %xmasked = and i8 %ymask, %x
  %r = sub i8 0, %xmasked

https://rise4fun.com/Alive/OIpla

This decreases use count of %x, may allow us to
later hoist said negation even further,
and results in marginally nicer X86 codegen.

See
  https://bugs.llvm.org/show_bug.cgi?id=44448
  https://reviews.llvm.org/D71499
This commit is contained in:
Roman Lebedev 2020-01-03 19:53:29 +03:00
parent b87a351182
commit cc0216bedb
No known key found for this signature in database
GPG Key ID: 083C3EBB4A1689E0
2 changed files with 22 additions and 12 deletions
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10
llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
View File

@ -1879,6 +1879,16 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) {
Y, Builder.CreateNot(Op1, Op1->getName() + ".not"));
}
{
// (sub (and Op1, (neg X)), Op1) --> neg (and Op1, (add X, -1))
Value *X;
if (match(Op0, m_OneUse(m_c_And(m_Specific(Op1),
m_OneUse(m_Neg(m_Value(X))))))) {
return BinaryOperator::CreateNeg(Builder.CreateAnd(
Op1, Builder.CreateAdd(X, Constant::getAllOnesValue(I.getType()))));
}
}
if (Op1->hasOneUse()) {
Value *X = nullptr, *Y = nullptr, *Z = nullptr;
Constant *C = nullptr;

24
llvm/test/Transforms/InstCombine/hoist-negation-out-of-bias-calculation.ll
View File

@ -14,9 +14,9 @@
define i8 @t0(i8 %x, i8 %y) {
; CHECK-LABEL: @t0(
; CHECK-NEXT: [[NEGY:%.*]] = sub i8 0, [[Y:%.*]]
; CHECK-NEXT: [[UNBIASEDX:%.*]] = and i8 [[NEGY]], [[X:%.*]]
; CHECK-NEXT: [[NEGBIAS:%.*]] = sub i8 [[UNBIASEDX]], [[X]]
; CHECK-NEXT: [[TMP1:%.*]] = add i8 [[Y:%.*]], -1
; CHECK-NEXT: [[TMP2:%.*]] = and i8 [[TMP1]], [[X:%.*]]
; CHECK-NEXT: [[NEGBIAS:%.*]] = sub i8 0, [[TMP2]]
; CHECK-NEXT: ret i8 [[NEGBIAS]]
;
%negy = sub i8 0, %y
@ -30,9 +30,9 @@ declare i8 @gen8()
define i8 @t1_commutative(i8 %y) {
; CHECK-LABEL: @t1_commutative(
; CHECK-NEXT: [[X:%.*]] = call i8 @gen8()
; CHECK-NEXT: [[NEGY:%.*]] = sub i8 0, [[Y:%.*]]
; CHECK-NEXT: [[UNBIASEDX:%.*]] = and i8 [[X]], [[NEGY]]
; CHECK-NEXT: [[NEGBIAS:%.*]] = sub i8 [[UNBIASEDX]], [[X]]
; CHECK-NEXT: [[TMP1:%.*]] = add i8 [[Y:%.*]], -1
; CHECK-NEXT: [[TMP2:%.*]] = and i8 [[X]], [[TMP1]]
; CHECK-NEXT: [[NEGBIAS:%.*]] = sub i8 0, [[TMP2]]
; CHECK-NEXT: ret i8 [[NEGBIAS]]
;
%x = call i8 @gen8()
@ -44,9 +44,9 @@ define i8 @t1_commutative(i8 %y) {
define <2 x i8> @t2_vec(<2 x i8> %x, <2 x i8> %y) {
; CHECK-LABEL: @t2_vec(
; CHECK-NEXT: [[NEGY:%.*]] = sub <2 x i8> zeroinitializer, [[Y:%.*]]
; CHECK-NEXT: [[UNBIASEDX:%.*]] = and <2 x i8> [[NEGY]], [[X:%.*]]
; CHECK-NEXT: [[NEGBIAS:%.*]] = sub <2 x i8> [[UNBIASEDX]], [[X]]
; CHECK-NEXT: [[TMP1:%.*]] = add <2 x i8> [[Y:%.*]], <i8 -1, i8 -1>
; CHECK-NEXT: [[TMP2:%.*]] = and <2 x i8> [[TMP1]], [[X:%.*]]
; CHECK-NEXT: [[NEGBIAS:%.*]] = sub <2 x i8> zeroinitializer, [[TMP2]]
; CHECK-NEXT: ret <2 x i8> [[NEGBIAS]]
;
%negy = sub <2 x i8> <i8 0, i8 0>, %y
@ -57,9 +57,9 @@ define <2 x i8> @t2_vec(<2 x i8> %x, <2 x i8> %y) {
define <2 x i8> @t3_vec_undef(<2 x i8> %x, <2 x i8> %y) {
; CHECK-LABEL: @t3_vec_undef(
; CHECK-NEXT: [[NEGY:%.*]] = sub <2 x i8> <i8 0, i8 undef>, [[Y:%.*]]
; CHECK-NEXT: [[UNBIASEDX:%.*]] = and <2 x i8> [[NEGY]], [[X:%.*]]
; CHECK-NEXT: [[NEGBIAS:%.*]] = sub <2 x i8> [[UNBIASEDX]], [[X]]
; CHECK-NEXT: [[TMP1:%.*]] = add <2 x i8> [[Y:%.*]], <i8 -1, i8 -1>
; CHECK-NEXT: [[TMP2:%.*]] = and <2 x i8> [[TMP1]], [[X:%.*]]
; CHECK-NEXT: [[NEGBIAS:%.*]] = sub <2 x i8> zeroinitializer, [[TMP2]]
; CHECK-NEXT: ret <2 x i8> [[NEGBIAS]]
;
%negy = sub <2 x i8> <i8 0, i8 undef>, %y