[InstCombine] Fold binary operator into select, when one of the opera…

[spaits]

…nd is the select's condition

It is a prototype that fixes #163108 .

This patch would fix all the possible cases described in the original issue and cases beyond that (other binary operators).

TODO:

• Extend testing
• Fix failing test cases in CI
• Integrate the function for arithmetic operations

[github-actions]

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View the diff from clang-format here.

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index e45cc7b0f..7f78c1349 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -370,13 +370,11 @@ static Instruction *foldBinOpIntoSelectWhenConditionIsOperand(Instruction &I) {
                               ConstantInt::get(Ty, SelLeft->getValue() ^ 1),
                               ConstantInt::get(Ty, SelRight->getValue() ^ 0));
   case Instruction::Add:
-    return SelectInst::Create(CommonInput,
-                              ConstantInt::get(Ty, SelLeft->getValue() + 1),
-                              SelRight);
+    return SelectInst::Create(
+        CommonInput, ConstantInt::get(Ty, SelLeft->getValue() + 1), SelRight);
   case Instruction::Sub:
-    return SelectInst::Create(CommonInput,
-                              ConstantInt::get(Ty, SelLeft->getValue() - 1),
-                              SelRight);
+    return SelectInst::Create(
+        CommonInput, ConstantInt::get(Ty, SelLeft->getValue() - 1), SelRight);
   case Instruction::Mul:
     return SelectInst::Create(CommonInput,
                               ConstantInt::get(Ty, SelLeft->getValue()),
@@ -2510,7 +2508,6 @@ Instruction *InstCombinerImpl::visitAnd(BinaryOperator &I) {
     return SelectInst::Create(Cmp, ConstantInt::getNullValue(Ty), Y);
   }
 
-
   if (Instruction *Res = foldBinOpIntoSelectWhenConditionIsOperand(I))
     return Res;
 
@@ -4167,7 +4164,6 @@ Instruction *InstCombinerImpl::visitOr(BinaryOperator &I) {
   if (Instruction *Res = foldBinOpIntoSelectWhenConditionIsOperand(I))
     return Res;
 
-
   // If the operands have no common bits set:
   // or (mul X, Y), X --> add (mul X, Y), X --> mul X, (Y + 1)
   if (match(&I, m_c_DisjointOr(m_OneUse(m_Mul(m_Value(X), m_Value(Y))),
@@ -5271,7 +5267,6 @@ Instruction *InstCombinerImpl::visitXor(BinaryOperator &I) {
   if (Instruction *Res = foldBinOpIntoSelectWhenConditionIsOperand(I))
     return Res;
 
-
   // Fold (X & M) ^ (Y & ~M) -> (X & M) | (Y & ~M)
   // This it a special case in haveNoCommonBitsSet, but the computeKnownBits
   // calls in there are unnecessary as SimplifyDemandedInstructionBits should

[andjo403]

maybe it is possible to handle this cases in

llvm-project/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp

Lines 1753 to 1765 in c193eea

	if (Op == SI) {
	V = IsTrueArm ? SI->getTrueValue() : SI->getFalseValue();
	} else if (match(SI->getCondition(),
	m_SpecificICmp(IsTrueArm ? ICmpInst::ICMP_EQ
	: ICmpInst::ICMP_NE,
	m_Specific(Op), m_Value(V))) &&
	isGuaranteedNotToBeUndefOrPoison(V)) {
	// Pass
	} else {
	V = Op;
	}
	Ops.push_back(V);
	}

by adding handling of cast something like

    else if (match(Op, m_ZExt(m_Specific(SI->getCondition())))) {
      V = IsTrueArm ? ConstantInt::get(Op->getType(), 1)
                    : ConstantInt::getNullValue(Op->getType());
    } else if (match(Op, m_SExt(m_Specific(SI->getCondition())))) {
      V = IsTrueArm ? ConstantInt::getAllOnesValue(Op->getType())
                    : ConstantInt::getNullValue(Op->getType());
    }

[spaits]

Thanks @andjo403 . It works! What to do next? Should I close this PR and you create another one with your code, since you came up with this elegant soultion. Or should I add the code to this PR and have you as another author?

[andjo403]

I created a PR with my solution now #166816

[andjo403]

as you mention Integrate the for arithmetic operations with a fast search it seems like foldBinOpIntoSelectOrPhi or FoldOpIntoSelect is only called for add/sub with one constant so maybe that can be something for you to continue with if it is not to compile time heavy.

also in foldBinOpIntoSelectOrPhi FoldOpIntoSelect is only called if the first operand is the select but do not think that is a must now that the second parameter is not always a constant.