[llvm] [SCEVPatternMatch] Extend with more matchers (PR #138836)

[Nikita Popov via llvm-commits]

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@@ -2864,20 +2863,8 @@ static const SCEV *getStrideFromPointer(Value *Ptr, ScalarEvolution *SE, Loop *L
 
   // Strip off the size of access multiplication if we are still analyzing the
   // pointer.
-  if (OrigPtr == Ptr) {
-    if (auto *M = dyn_cast<SCEVMulExpr>(V)) {
-      auto *StepConst = dyn_cast<SCEVConstant>(M->getOperand(0));
-      if (!StepConst)
-        return nullptr;
-
-      auto StepVal = StepConst->getAPInt().trySExtValue();
-      // Bail out on a non-unit pointer access size.
-      if (!StepVal || StepVal != 1)
-        return nullptr;
-
-      V = M->getOperand(1);
-    }
-  }
+  if (OrigPtr == Ptr)
+    match(V, m_scev_Mul(m_scev_SpecificInt(1), m_SCEV(V)));
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nikic wrote:

So, this code is very weird. Your new code is never going to match anything, because a `1 * V` SCEV would fold to `V` at construction. What the old code did was effectively just reject any multiply, but... I think the old code was effectively dead because in the `OrigPtr == Ptr` case we're working on a pointer SCEV rather than an index, and a pointer SCEV cannot be multiplied.

So I think the correct thing to do would be to remove this entire if block. But we should do that in a separate change, not as part of this one.

https://github.com/llvm/llvm-project/pull/138836