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[InstCombine] fold negate disguised as select+mul

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Name: negate if true
  %sel = select i1 %cond, i32 -1, i32 1
  %r = mul i32 %sel, %x
  =>
  %m = sub i32 0, %x
  %r = select i1 %cond, i32 %m, i32 %x

  Name: negate if false
  %sel = select i1 %cond, i32 1, i32 -1
  %r = mul i32 %sel, %x
  =>
  %m = sub i32 0, %x
  %r = select i1 %cond, i32 %x, i32 %m

https://rise4fun.com/Alive/Nlh

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@373230 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Sanjay Patel
2019-09-30 17:02:26 +00:00
parent 1da64d7038
commit 8177e21eb0
2 changed files with 31 additions and 8 deletions
Download Patch File Download Diff File Expand all files Collapse all files
lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+19
View File
@@ -213,6 +213,25 @@ Instruction *InstCombiner::visitMul(BinaryOperator &I) {
if (Instruction *FoldedMul = foldBinOpIntoSelectOrPhi(I))
return FoldedMul;
// TODO: This is a specific form of a much more general pattern.
// We could detect a select with any binop identity constant, or we
// could use SimplifyBinOp to see if either arm of the select reduces.
// But that needs to be done carefully and/or while removing potential
// reverse canonicalizations as in InstCombiner::foldSelectIntoOp().
// mul (select Cond, 1, -1), Op1 --> select Cond, Op1, -Op1
// mul (select Cond, -1, 1), Op1 --> select Cond, -Op1, Op1
// mul Op0, (select Cond, 1, -1) --> select Cond, Op0, -Op0
// mul Op0, (select Cond, -1, 1) --> select Cond, -Op0, Op0
Value *Cond;
if (match(Op0, m_OneUse(m_Select(m_Value(Cond), m_One(), m_AllOnes()))))
return SelectInst::Create(Cond, Op1, Builder.CreateNeg(Op1));
if (match(Op0, m_OneUse(m_Select(m_Value(Cond), m_AllOnes(), m_One()))))
return SelectInst::Create(Cond, Builder.CreateNeg(Op1), Op1);
if (match(Op1, m_OneUse(m_Select(m_Value(Cond), m_One(), m_AllOnes()))))
return SelectInst::Create(Cond, Op0, Builder.CreateNeg(Op0));
if (match(Op1, m_OneUse(m_Select(m_Value(Cond), m_AllOnes(), m_One()))))
return SelectInst::Create(Cond, Builder.CreateNeg(Op0), Op0);
// Simplify mul instructions with a constant RHS.
if (isa<Constant>(Op1)) {
// Canonicalize (X+C1)*CI -> X*CI+C1*CI.
test/Transforms/InstCombine/mul.ll
+12 -8
View File
@@ -520,8 +520,8 @@ define i64 @test_mul_canonicalize_neg_is_not_undone(i64 %L1) {
define i32 @negate_if_true(i32 %x, i1 %cond) {
; CHECK-LABEL: @negate_if_true(
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[COND:%.*]], i32 -1, i32 1
; CHECK-NEXT: [[R:%.*]] = mul i32 [[SEL]], [[X:%.*]]
; CHECK-NEXT: [[TMP1:%.*]] = sub i32 0, [[X:%.*]]
; CHECK-NEXT: [[R:%.*]] = select i1 [[COND:%.*]], i32 [[TMP1]], i32 [[X]]
; CHECK-NEXT: ret i32 [[R]]
;
%sel = select i1 %cond, i32 -1, i32 1
@@ -531,8 +531,8 @@ define i32 @negate_if_true(i32 %x, i1 %cond) {
define i32 @negate_if_false(i32 %x, i1 %cond) {
; CHECK-LABEL: @negate_if_false(
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[COND:%.*]], i32 1, i32 -1
; CHECK-NEXT: [[R:%.*]] = mul i32 [[SEL]], [[X:%.*]]
; CHECK-NEXT: [[TMP1:%.*]] = sub i32 0, [[X:%.*]]
; CHECK-NEXT: [[R:%.*]] = select i1 [[COND:%.*]], i32 [[X]], i32 [[TMP1]]
; CHECK-NEXT: ret i32 [[R]]
;
%sel = select i1 %cond, i32 1, i32 -1
@@ -543,8 +543,8 @@ define i32 @negate_if_false(i32 %x, i1 %cond) {
define <2 x i8> @negate_if_true_commute(<2 x i8> %px, i1 %cond) {
; CHECK-LABEL: @negate_if_true_commute(
; CHECK-NEXT: [[X:%.*]] = sdiv <2 x i8> <i8 42, i8 42>, [[PX:%.*]]
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[COND:%.*]], <2 x i8> <i8 -1, i8 -1>, <2 x i8> <i8 1, i8 1>
; CHECK-NEXT: [[R:%.*]] = mul <2 x i8> [[X]], [[SEL]]
; CHECK-NEXT: [[TMP1:%.*]] = sub nsw <2 x i8> zeroinitializer, [[X]]
; CHECK-NEXT: [[R:%.*]] = select i1 [[COND:%.*]], <2 x i8> [[TMP1]], <2 x i8> [[X]]
; CHECK-NEXT: ret <2 x i8> [[R]]
;
%x = sdiv <2 x i8> <i8 42, i8 42>, %px ; thwart complexity-based canonicalization
@@ -556,8 +556,8 @@ define <2 x i8> @negate_if_true_commute(<2 x i8> %px, i1 %cond) {
define <2 x i8> @negate_if_false_commute(<2 x i8> %px, <2 x i1> %cond) {
; CHECK-LABEL: @negate_if_false_commute(
; CHECK-NEXT: [[X:%.*]] = sdiv <2 x i8> <i8 42, i8 5>, [[PX:%.*]]
; CHECK-NEXT: [[SEL:%.*]] = select <2 x i1> [[COND:%.*]], <2 x i8> <i8 1, i8 undef>, <2 x i8> <i8 -1, i8 -1>
; CHECK-NEXT: [[R:%.*]] = mul <2 x i8> [[X]], [[SEL]]
; CHECK-NEXT: [[TMP1:%.*]] = sub <2 x i8> zeroinitializer, [[X]]
; CHECK-NEXT: [[R:%.*]] = select <2 x i1> [[COND:%.*]], <2 x i8> [[X]], <2 x i8> [[TMP1]]
; CHECK-NEXT: ret <2 x i8> [[R]]
;
%x = sdiv <2 x i8> <i8 42, i8 5>, %px ; thwart complexity-based canonicalization
@@ -566,6 +566,8 @@ define <2 x i8> @negate_if_false_commute(<2 x i8> %px, <2 x i1> %cond) {
ret <2 x i8> %r
}
; Negative test
define i32 @negate_if_true_extra_use(i32 %x, i1 %cond) {
; CHECK-LABEL: @negate_if_true_extra_use(
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[COND:%.*]], i32 -1, i32 1
@@ -579,6 +581,8 @@ define i32 @negate_if_true_extra_use(i32 %x, i1 %cond) {
ret i32 %r
}
; Negative test
define <2 x i8> @negate_if_true_wrong_constant(<2 x i8> %px, i1 %cond) {
; CHECK-LABEL: @negate_if_true_wrong_constant(
; CHECK-NEXT: [[X:%.*]] = sdiv <2 x i8> <i8 42, i8 42>, [[PX:%.*]]