[InstCombine] Simplify and/or of icmp eq with op replacement #70335
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@@ -2025,6 +2025,52 @@ static Value *simplifyAndOrOfCmps(const SimplifyQuery &Q, Value *Op0, | |
| return nullptr; | ||
| } | ||
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| static Value *simplifyWithOpReplaced(Value *V, Value *Op, Value *RepOp, | ||
| const SimplifyQuery &Q, | ||
| bool AllowRefinement, | ||
| SmallVectorImpl<Instruction *> *DropFlags, | ||
| unsigned MaxRecurse); | ||
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| static Value *simplifyAndOrWithICmpEq(unsigned Opcode, Value *Op0, Value *Op1, | ||
| const SimplifyQuery &Q, | ||
| unsigned MaxRecurse) { | ||
| assert((Opcode == Instruction::And || Opcode == Instruction::Or) && | ||
| "Must be and/or"); | ||
| ICmpInst::Predicate Pred; | ||
| Value *A, *B; | ||
| if (!match(Op0, m_ICmp(Pred, m_Value(A), m_Value(B))) || | ||
| !ICmpInst::isEquality(Pred) || !MaxRecurse--) | ||
| return nullptr; | ||
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| auto Simplify = [&](Value *Res) -> Value * { | ||
| // and (icmp eq a, b), x implies (a==b) inside x. | ||
| // or (icmp ne a, b), x implies (a==b) inside x. | ||
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There was a problem hiding this comment. Do you get any benefit There was a problem hiding this comment. If we had a way to say "simplify x under the assumption that a != b", I would expect that to be beneficial. But we can only do this for equalities right now, as in that case we can just replace operands. I think we need some generic way to say "evaluate this predicate under the assumption that v has range CR" -- some of @dtcxzyw's recent PRs go in that direction, but I feel like there must be a more generic solution to this, which integrates with existing range propagation logic, instead of reimplementing it in parts. This seems like something that LVI/CVP should be doing, but I don't see a good way to integrate it there. |
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| // If x simplifies to true/false, we can simplify the and/or. | ||
| if (Pred == | ||
| (Opcode == Instruction::And ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_NE)) | ||
| return simplifyBinOp(Opcode, Op0, Res, Q, MaxRecurse); | ||
| // If we have and (icmp ne a, b), x and for a==b we can simplify x to false, | ||
| // then we can drop the icmp, as x will already be false in the case where | ||
| // the icmp is false. Similar for or and true. | ||
| if (Res == ConstantExpr::getBinOpAbsorber(Opcode, Res->getType())) | ||
| return Op1; | ||
| return nullptr; | ||
| }; | ||
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| // Increment MaxRecurse again, because simplifyWithOpReplaced() does its own | ||
| // decrement. | ||
| if (Value *Res = | ||
| simplifyWithOpReplaced(Op1, A, B, Q, /* AllowRefinement */ true, | ||
| /* DropFlags */ nullptr, MaxRecurse + 1)) | ||
| return Simplify(Res); | ||
| if (Value *Res = | ||
| simplifyWithOpReplaced(Op1, B, A, Q, /* AllowRefinement */ true, | ||
| /* DropFlags */ nullptr, MaxRecurse + 1)) | ||
| return Simplify(Res); | ||
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| return nullptr; | ||
| } | ||
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| /// Given a bitwise logic op, check if the operands are add/sub with a common | ||
| /// source value and inverted constant (identity: C - X -> ~(X + ~C)). | ||
| static Value *simplifyLogicOfAddSub(Value *Op0, Value *Op1, | ||
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@@ -2159,6 +2205,13 @@ static Value *simplifyAndInst(Value *Op0, Value *Op1, const SimplifyQuery &Q, | |
| isKnownToBeAPowerOfTwo(Op0, Q.DL, /*OrZero*/ true, 0, Q.AC, Q.CxtI, Q.DT)) | ||
| return Constant::getNullValue(Op0->getType()); | ||
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| if (Value *V = | ||
| simplifyAndOrWithICmpEq(Instruction::And, Op0, Op1, Q, MaxRecurse)) | ||
| return V; | ||
| if (Value *V = | ||
| simplifyAndOrWithICmpEq(Instruction::And, Op1, Op0, Q, MaxRecurse)) | ||
| return V; | ||
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| if (Value *V = simplifyAndOrOfCmps(Q, Op0, Op1, true)) | ||
| return V; | ||
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@@ -2435,6 +2488,13 @@ static Value *simplifyOrInst(Value *Op0, Value *Op1, const SimplifyQuery &Q, | |
| match(Op0, m_LShr(m_Specific(X), m_Specific(Y)))) | ||
| return Op1; | ||
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| if (Value *V = | ||
| simplifyAndOrWithICmpEq(Instruction::Or, Op0, Op1, Q, MaxRecurse)) | ||
| return V; | ||
| if (Value *V = | ||
| simplifyAndOrWithICmpEq(Instruction::Or, Op1, Op0, Q, MaxRecurse)) | ||
| return V; | ||
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| if (Value *V = simplifyAndOrOfCmps(Q, Op0, Op1, false)) | ||
| return V; | ||
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nit: Would have recursive check first.