[InstCombine] add folds for binop with sexted bool and constant operands

This is a generalization/extension of the existing and/or
folds noted with TODO comments. Those have a one-use
constraint that is not necessary.

Potential follow-ups are noted by the TODO comments in
the new function. We can also call this function from
other binop visit* functions, but we need to add tests
first.

This solves:
https://llvm.org/PR52543

https://alive2.llvm.org/ce/z/NWuCR5

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 06c9bf6..4ef7ff3 100644 (file)
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -2061,7 +2061,14 @@ Instruction *InstCombinerImpl::visitAnd(BinaryOperator &I) {
   if (Instruction *CastedAnd = foldCastedBitwiseLogic(I))
     return CastedAnd;
 
+  if (Instruction *Sel = foldBinopOfSextBoolToSelect(I))
+    return Sel;
+
   // and(sext(A), B) / and(B, sext(A)) --> A ? B : 0, where A is i1 or <N x i1>.
+  // TODO: Move this into foldBinopOfSextBoolToSelect as a more generalized fold
+  //       with binop identity constant. But creating a select with non-constant
+  //       arm may not be reversible due to poison semantics. Is that a good
+  //       canonicalization?
   Value *A;
   if (match(Op0, m_OneUse(m_SExt(m_Value(A)))) &&
       A->getType()->isIntOrIntVectorTy(1))
@@ -2788,7 +2795,14 @@ Instruction *InstCombinerImpl::visitOr(BinaryOperator &I) {
   if (Instruction *CastedOr = foldCastedBitwiseLogic(I))
     return CastedOr;
 
+  if (Instruction *Sel = foldBinopOfSextBoolToSelect(I))
+    return Sel;
+
   // or(sext(A), B) / or(B, sext(A)) --> A ? -1 : B, where A is i1 or <N x i1>.
+  // TODO: Move this into foldBinopOfSextBoolToSelect as a more generalized fold
+  //       with binop identity constant. But creating a select with non-constant
+  //       arm may not be reversible due to poison semantics. Is that a good
+  //       canonicalization?
   if (match(Op0, m_OneUse(m_SExt(m_Value(A)))) &&
       A->getType()->isIntOrIntVectorTy(1))
     return SelectInst::Create(A, ConstantInt::getSigned(I.getType(), -1), Op1);

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
index 72e1b21..20c7518 100644 (file)
--- a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
@@ -319,6 +319,7 @@ private:
   Instruction *scalarizePHI(ExtractElementInst &EI, PHINode *PN);
   Instruction *foldBitcastExtElt(ExtractElementInst &ExtElt);
   Instruction *foldCastedBitwiseLogic(BinaryOperator &I);
+  Instruction *foldBinopOfSextBoolToSelect(BinaryOperator &I);
   Instruction *narrowBinOp(TruncInst &Trunc);
   Instruction *narrowMaskedBinOp(BinaryOperator &And);
   Instruction *narrowMathIfNoOverflow(BinaryOperator &I);

diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 47b6dcb..1f81624 100644 (file)
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -967,6 +967,29 @@ Value *InstCombinerImpl::dyn_castNegVal(Value *V) const {
   return nullptr;
 }
 
+/// A binop with a constant operand and a sign-extended boolean operand may be
+/// converted into a select of constants by applying the binary operation to
+/// the constant with the two possible values of the extended boolean (0 or -1).
+Instruction *InstCombinerImpl::foldBinopOfSextBoolToSelect(BinaryOperator &BO) {
+  // TODO: Handle non-commutative binop (constant is operand 0).
+  // TODO: Handle zext.
+  // TODO: Peek through 'not' of cast.
+  Value *BO0 = BO.getOperand(0);
+  Value *BO1 = BO.getOperand(1);
+  Value *X;
+  Constant *C;
+  if (!match(BO0, m_SExt(m_Value(X))) || !match(BO1, m_ImmConstant(C)) ||
+      !X->getType()->isIntOrIntVectorTy(1))
+    return nullptr;
+
+  // bo (sext i1 X), C --> select X, (bo -1, C), (bo 0, C)
+  Constant *Ones = ConstantInt::getAllOnesValue(BO.getType());
+  Constant *Zero = ConstantInt::getNullValue(BO.getType());
+  Constant *TVal = ConstantExpr::get(BO.getOpcode(), Ones, C);
+  Constant *FVal = ConstantExpr::get(BO.getOpcode(), Zero, C);
+  return SelectInst::Create(X, TVal, FVal);
+}
+
 static Value *foldOperationIntoSelectOperand(Instruction &I, Value *SO,
                                              InstCombiner::BuilderTy &Builder) {
   if (auto *Cast = dyn_cast<CastInst>(&I))

diff --git a/llvm/test/Transforms/InstCombine/and.ll b/llvm/test/Transforms/InstCombine/and.ll
index ec16ffc..c5b624b 100644 (file)
--- a/llvm/test/Transforms/InstCombine/and.ll
+++ b/llvm/test/Transforms/InstCombine/and.ll
@@ -1510,7 +1510,7 @@ define i32 @sext_to_sel_multi_use_constant_mask(i1 %y) {
 ; CHECK-LABEL: @sext_to_sel_multi_use_constant_mask(
 ; CHECK-NEXT:    [[SEXT:%.*]] = sext i1 [[Y:%.*]] to i32
 ; CHECK-NEXT:    call void @use32(i32 [[SEXT]])
-; CHECK-NEXT:    [[R:%.*]] = and i32 [[SEXT]], 42
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[Y]], i32 42, i32 0
 ; CHECK-NEXT:    ret i32 [[R]]
 ;
   %sext = sext i1 %y to i32

diff --git a/llvm/test/Transforms/InstCombine/or.ll b/llvm/test/Transforms/InstCombine/or.ll
index 6426612..376ae78 100644 (file)
--- a/llvm/test/Transforms/InstCombine/or.ll
+++ b/llvm/test/Transforms/InstCombine/or.ll
@@ -657,7 +657,7 @@ define i32 @sext_to_sel_multi_use_constant_mask(i1 %y) {
 ; CHECK-LABEL: @sext_to_sel_multi_use_constant_mask(
 ; CHECK-NEXT:    [[SEXT:%.*]] = sext i1 [[Y:%.*]] to i32
 ; CHECK-NEXT:    call void @use(i32 [[SEXT]])
-; CHECK-NEXT:    [[R:%.*]] = or i32 [[SEXT]], 42
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[Y]], i32 -1, i32 42
 ; CHECK-NEXT:    ret i32 [[R]]
 ;
   %sext = sext i1 %y to i32