[llvm] [Attributor] Propagate alignment through ptrmask (PR #150158)

[Krzysztof Drewniak via llvm-commits]

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@@ -5200,6 +5201,28 @@ static unsigned getKnownAlignForUse(Attributor &A, AAAlign &QueryingAA,
       TrackUse = true;
     return 0;
   }
+  if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
+    switch (II->getIntrinsicID()) {
+    case Intrinsic::ptrmask: {
+      // Is it appropriate to pull attribute in initialization?
+      const auto *ConstVals = A.getAAFor<AAPotentialConstantValues>(
+          QueryingAA, IRPosition::value(*II->getOperand(1)), DepClassTy::NONE);
+      const auto *AlignAA = A.getAAFor<AAAlign>(
+          QueryingAA, IRPosition::value(*II), DepClassTy::NONE);
+      if (ConstVals && ConstVals->isValidState() && ConstVals->isAtFixpoint()) {
+        unsigned ShiftValue = std::min(ConstVals->getAssumedMinTrailingZeros(),
+                                       Value::MaxAlignmentExponent);
+        Align ConstAlign(UINT64_C(1) << ShiftValue);
+        if (ConstAlign >= AlignAA->getKnownAlign())
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krzysz00 wrote:

I might just not be understanding the attributor very well, but it seems weird that we're setting align 1 here. I assume it's because there's some handling later that fixes this case?

I can tell from the tests that all this code is doing what I'd intuitively expect, so I'll just let myself be confused.

https://github.com/llvm/llvm-project/pull/150158