[ValueTracking] Infer NonEqual from dominating conditions/assumptions #117442
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@@ -3857,6 +3857,50 @@ static bool isKnownNonEqual(const Value *V1, const Value *V2, | |
| match(V2, m_PtrToIntSameSize(Q.DL, m_Value(B)))) | ||
| return isKnownNonEqual(A, B, DemandedElts, Depth + 1, Q); | ||
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| if (!Q.CxtI) | ||
| return false; | ||
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| // Try to infer NonEqual based on information from dominating conditions. | ||
| if (Q.DC && Q.DT) { | ||
| for (BranchInst *BI : Q.DC->conditionsFor(V1)) { | ||
| Value *Cond = BI->getCondition(); | ||
| BasicBlockEdge Edge0(BI->getParent(), BI->getSuccessor(0)); | ||
| if (Q.DT->dominates(Edge0, Q.CxtI->getParent()) && | ||
| isImpliedCondition(Cond, ICmpInst::ICMP_NE, V1, V2, Q.DL, | ||
| /*LHSIsTrue=*/true, Depth) | ||
| .value_or(false)) | ||
| return true; | ||
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| BasicBlockEdge Edge1(BI->getParent(), BI->getSuccessor(1)); | ||
| if (Q.DT->dominates(Edge1, Q.CxtI->getParent()) && | ||
| isImpliedCondition(Cond, ICmpInst::ICMP_NE, V1, V2, Q.DL, | ||
| /*LHSIsTrue=*/false, Depth) | ||
| .value_or(false)) | ||
| return true; | ||
| } | ||
| } | ||
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| if (!Q.AC) | ||
| return false; | ||
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| // Try to infer NonEqual based on information from assumptions. | ||
| for (auto &AssumeVH : Q.AC->assumptionsFor(V1)) { | ||
| if (!AssumeVH) | ||
| continue; | ||
| CallInst *I = cast<CallInst>(AssumeVH); | ||
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| assert(I->getFunction() == Q.CxtI->getFunction() && | ||
| "Got assumption for the wrong function!"); | ||
| assert(I->getIntrinsicID() == Intrinsic::assume && | ||
| "must be an assume intrinsic"); | ||
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| if (isImpliedCondition(I->getArgOperand(0), ICmpInst::ICMP_NE, V1, V2, Q.DL, | ||
| /*LHSIsTrue=*/true, Depth) | ||
| .value_or(false) && | ||
| isValidAssumeForContext(I, Q.CxtI, Q.DT)) | ||
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There was a problem hiding this comment. Check that assume is valid before recursive function? There was a problem hiding this comment. It seems slower than current implementation: https://llvm-compile-time-tracker.com/compare.php?from=8b5145c718a41f1cbfe463def3ad88a89afb17e8&to=eb913e9188a5ae48bdf48d714a95f0f75731e21f&stat=instructions:u |
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| return true; | ||
| } | ||
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There was a problem hiding this comment. nit: Maybe nicer to have a helper |
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| return false; | ||
| } | ||
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@@ -10231,10 +10275,10 @@ void llvm::findValuesAffectedByCondition( | |
| Worklist.push_back(B); | ||
| } | ||
| } else if (match(V, m_ICmp(Pred, m_Value(A), m_Value(B)))) { | ||
| bool HasRHSC = match(B, m_ConstantInt()); | ||
| if (ICmpInst::isEquality(Pred)) { | ||
| AddAffected(A); | ||
| AddAffected(B); | ||
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There was a problem hiding this comment. There was a problem hiding this comment. Is the impact here mainly from adding more affected values or from using them in isKnownNonEqual? Something we could do is add a bitfield for what the affected value is for (e.g. knownbits, etc), so we can quickly skip ones that are not relevant. There was a problem hiding this comment. It is mainly from adding more affected values. There was a problem hiding this comment.
Are you working on this? There was a problem hiding this comment. I have implemented a prototype (see #118493). But the compile-time impact looks worse: http://llvm-compile-time-tracker.com/compare.php?from=8f3cf204bb91ce09fb3651b8a7e770de7e603b2f&to=338d7fc5b72e20f1606a28f740d5a0068c95d94b&stat=instructions%3Au |
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| if (HasRHSC) { | ||
| Value *Y; | ||
| // (X & C) or (X | C). | ||
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@@ -10248,6 +10292,7 @@ void llvm::findValuesAffectedByCondition( | |
| } | ||
| } | ||
| } else { | ||
| AddCmpOperands(A, B); | ||
| if (HasRHSC) { | ||
| // Handle (A + C1) u< C2, which is the canonical form of | ||
| // A > C3 && A < C4. | ||
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Here and above, any value in iterating through V2 as well?
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We add both
V1andV2infindValuesAffectedByCondition. So it is ok to iterate on conditions related toV1.