[ValueTracking] Check both operands for being 0 and then the other for isKnownNonZero #147330
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llvmbot
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llvm:analysis
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@llvm/pr-subscribers-llvm-analysis Author: AZero13 (AZero13) ChangesFull diff: https://github.com/llvm/llvm-project/pull/147330.diff 1 Files Affected:
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 09745ed6eac6a..a8f5728c940b1 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -2880,11 +2880,6 @@ static bool isNonZeroSub(const APInt &DemandedElts, const SimplifyQuery &Q,
if (matchOpWithOpEqZero(X, Y))
return true;
- // TODO: Move this case into isKnownNonEqual().
- if (auto *C = dyn_cast<Constant>(X))
- if (C->isNullValue() && isKnownNonZero(Y, DemandedElts, Q, Depth))
- return true;
-
return ::isKnownNonEqual(X, Y, DemandedElts, Q, Depth);
}
@@ -3892,6 +3887,12 @@ static bool isKnownNonEqual(const Value *V1, const Value *V2,
if (Depth >= MaxAnalysisRecursionDepth)
return false;
+ // 0 vs known-non-zero => definitely different
+ if (match(V1, m_Zero()) && isKnownNonZero(V2, DemandedElts, Q, Depth + 1))
+ return true;
+ if (match(V2, m_Zero()) && isKnownNonZero(V1, DemandedElts, Q, Depth + 1))
+ return true;
+
// See if we can recurse through (exactly one of) our operands. This
// requires our operation be 1-to-1 and map every input value to exactly
// one output value. Such an operation is invertible.
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@dtcxzyw Can you please run the opt-benchmark so I can make tests |
AZero13
changed the title
|
✅ With the latest revision this PR passed the C/C++ code formatter. |
nikic
reviewed
Jul 9, 2025
| if (match(V1, m_Zero()) && isKnownNonZero(V2, DemandedElts, Q, Depth + 1)) | ||
| return true; | ||
| if (match(V2, m_Zero()) && isKnownNonZero(V1, DemandedElts, Q, Depth + 1)) | ||
| return true; |
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I don't think this makes sense. x - 0 is just x and should get folded away.
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We should check both operands, not just the first one.