[llvm] [ValueTracking] isNonEqual Pointers with with a recursive GEP (PR #70459)
David Sherwood via llvm-commits
llvm-commits at lists.llvm.org
Fri Dec 8 09:13:36 PST 2023
================
@@ -3141,6 +3141,63 @@ static bool isNonEqualSelect(const Value *V1, const Value *V2, unsigned Depth,
isKnownNonEqual(SI1->getFalseValue(), V2, Depth + 1, Q);
}
+static bool isNonEqualPointersWithRecursiveGEP(const Value *A, const Value *B,
+ unsigned Depth,
+ const SimplifyQuery &Q) {
+ // Where A is a recursive GEP for an incoming value of PHI indicating a
+ // loop. B can be a ptr/GEP.
+ // If the PHI has 2 incoming values, one of it being the recursive GEP A
+ // and other a ptr at same base and at an same/higher offset than B we are
+ // only incrementing the pointer further in loop if offset of recursive GEP is
+ // greater than 0.
+ if (!A->getType()->isPointerTy() || !B->getType()->isPointerTy())
+ return false;
+
+ auto *GEPA = dyn_cast<GEPOperator>(A);
+ // Is of type GEP.
+ if (!GEPA)
+ return false;
+
+ // Handle 2 incoming PHI values with one being a recursive GEP.
+ auto *PN = dyn_cast<PHINode>(GEPA->getPointerOperand());
+ if (!PN || PN->getNumIncomingValues() != 2)
+ return false;
+
+ // Recursive GEP in second incoming value. Always keep Recursive GEP as
+ // Step
+ Value *Start = nullptr, *Step = nullptr;
+ for (unsigned i = 0; i != 2; ++i) {
+ // Check if A is a Recursive GEP in one of the incoming values.
+ if (PN->getIncomingValue(i) == A && GEPA->getNumIndices() == 1 &&
+ isa<Constant>(GEPA->idx_begin())) {
+ Step = PN->getIncomingValue(i);
+ Start = PN->getIncomingValue(1 - i);
+ continue;
+ }
+ }
+ if (Start == nullptr || Step == nullptr)
+ return false;
+
+ // Other incoming node base should match the B base.
+ // StartOffset >= OffsetB && StepOffset > 0?
+ // StartOffset <= OffsetB && StepOffset < 0?
+ // Is non-equal if above are true.
+ APInt StartOffset(Q.DL.getIndexTypeSizeInBits(Start->getType()), 0);
----------------
david-arm wrote:
It looks like `stripAndAccumulateInBoundsConstantOffsets` invokes `stripAndAccumulateConstantOffsets` with `AllowNonInbounds=false` so we don't permit stripping of non-inbounds GEPs. Perhaps it's worth adding a comment somewhere explaining this won't currently work for such GEPs?
https://github.com/llvm/llvm-project/pull/70459
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