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

[via llvm-commits]

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@@ -5187,6 +5187,59 @@ struct AADereferenceableCallSiteReturned final
 // ------------------------ Align Argument Attribute ------------------------
 
 namespace {
+
+Align getKnownAlignForIntrinsic(Attributor &A, AAAlign &QueryingAA,
+                                const IntrinsicInst &II) {
+  switch (II.getIntrinsicID()) {
+  case Intrinsic::ptrmask: {
+    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(), (unsigned)63);
+      Align ConstAlign(1 << ShiftValue);
+      if (ConstAlign >= AlignAA->getKnownAlign())
+        return Align(1);
----------------
Shoreshen wrote:

Hi @arsenm , assume we have `%p = llvm.ptrmask(%x, %mask)` and `AlignAA` is for `%p`, `ConstAlign` is for `%mask`.

>From the definition of `AAAlign:: Known` we know that `%p` is at least aligned at `AlignAA->getKnownAlign()`. Then if `ConstAlign >= AlignAA->getKnownAlign()` happens, we know that `%mask` is going to cover the alignment requirement of `%p`.

Which actually means that `%x`'s alignment can be lower then `AlignAA->getKnownAlign()`.

In summary, this user of `%x` do not provide any information for the minimum alignment of `%x`


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