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| author | Sanjay Patel <spatel@rotateright.com> | 2021-10-28 08:11:59 -0400 |
|---|---|---|
| committer | Sanjay Patel <spatel@rotateright.com> | 2021-10-28 08:35:58 -0400 |
| commit | e8535fa78458abe37e54e5c01d52558c5e284092 (patch) | |
| tree | ee6455fb2146dffc450f5904387f4171c7650bae | |
| parent | 98f08752f76b80a509037986d620b402c48f5115 (diff) | |
| download | llvm-e8535fa78458abe37e54e5c01d52558c5e284092.tar.gz | |
[InstCombine] allow Negator to fold multi-use select with constant arms
The motivating test is reduced from:
https://llvm.org/PR52261
Note that the more general problem of folding any binop into a multi-use
select of constants is still there. We need to ease the restriction in
InstCombinerImpl::FoldOpIntoSelect() to catch those. But these examples
never reach that code because Negator exclusively handles negation
patterns within visitSub().
Differential Revision: https://reviews.llvm.org/D112657
| -rw-r--r-- | llvm/lib/Transforms/InstCombine/InstCombineNegator.cpp | 14 | ||||
| -rw-r--r-- | llvm/test/Transforms/InstCombine/sub-of-negatible.ll | 11 |
2 files changed, 18 insertions, 7 deletions
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineNegator.cpp b/llvm/lib/Transforms/InstCombine/InstCombineNegator.cpp index 37c7e6135501..7dc516c6fdc3 100644 --- a/llvm/lib/Transforms/InstCombine/InstCombineNegator.cpp +++ b/llvm/lib/Transforms/InstCombine/InstCombineNegator.cpp @@ -215,6 +215,20 @@ LLVM_NODISCARD Value *Negator::visitImpl(Value *V, unsigned Depth) { : Builder.CreateSExt(I->getOperand(0), I->getType(), I->getName() + ".neg"); break; + case Instruction::Select: { + // If both arms of the select are constants, we don't need to recurse. + // Therefore, this transform is not limited by uses. + auto *Sel = cast<SelectInst>(I); + Constant *TrueC, *FalseC; + if (match(Sel->getTrueValue(), m_ImmConstant(TrueC)) && + match(Sel->getFalseValue(), m_ImmConstant(FalseC))) { + Constant *NegTrueC = ConstantExpr::getNeg(TrueC); + Constant *NegFalseC = ConstantExpr::getNeg(FalseC); + return Builder.CreateSelect(Sel->getCondition(), NegTrueC, NegFalseC, + I->getName() + ".neg", /*MDFrom=*/I); + } + break; + } default: break; // Other instructions require recursive reasoning. } diff --git a/llvm/test/Transforms/InstCombine/sub-of-negatible.ll b/llvm/test/Transforms/InstCombine/sub-of-negatible.ll index 6c6fdbf35ed1..67abc286298a 100644 --- a/llvm/test/Transforms/InstCombine/sub-of-negatible.ll +++ b/llvm/test/Transforms/InstCombine/sub-of-negatible.ll @@ -98,10 +98,10 @@ define i8 @t4(i8 %x, i1 %y) { define i8 @select_of_constants_multi_use(i1 %b) { ; CHECK-LABEL: @select_of_constants_multi_use( -; CHECK-NEXT: [[S:%.*]] = select i1 [[B:%.*]], i8 42, i8 -2 +; CHECK-NEXT: [[S_NEG:%.*]] = select i1 [[B:%.*]], i8 -42, i8 2 +; CHECK-NEXT: [[S:%.*]] = select i1 [[B]], i8 42, i8 -2 ; CHECK-NEXT: call void @use8(i8 [[S]]) -; CHECK-NEXT: [[N:%.*]] = sub nsw i8 0, [[S]] -; CHECK-NEXT: ret i8 [[N]] +; CHECK-NEXT: ret i8 [[S_NEG]] ; %s = select i1 %b, i8 42, i8 -2 call void @use8(i8 %s) @@ -111,10 +111,7 @@ define i8 @select_of_constants_multi_use(i1 %b) { define i32 @PR52261(i1 %b) { ; CHECK-LABEL: @PR52261( -; CHECK-NEXT: [[S:%.*]] = select i1 [[B:%.*]], i32 2, i32 -2 -; CHECK-NEXT: [[N:%.*]] = sub nsw i32 0, [[S]] -; CHECK-NEXT: [[A:%.*]] = and i32 [[S]], [[N]] -; CHECK-NEXT: ret i32 [[A]] +; CHECK-NEXT: ret i32 2 ; %s = select i1 %b, i32 2, i32 -2 %n = sub nsw i32 0, %s |