[llvm] [AA] Refine ModRefInfo taking into account `errnomem` location (PR #157495)

[Nikita Popov via llvm-commits]

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@@ -997,6 +998,19 @@ ModRefInfo BasicAAResult::getModRefInfo(const CallBase *Call,
   }
 
   ModRefInfo Result = ArgMR | OtherMR;
+
+  // Refine accesses to errno memory. We can safely exclude the errno location
+  // if the given memory location is an identified function-local object, the
+  // size of the memory access is larger than the integer size, or if TBAA
+  // proves it does not alias errno.
+  if ((ErrnoMR | Result) != Result) {
+    if (isModOrRefSet(ErrnoMR) && !isIdentifiedFunctionLocal(Object) &&
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nikic wrote:

I don't think the isModOrRefSet() check is needed, it is already covered by `(ErrnoMR | Result) != Result`.

Also I think the isIdentifiedFunctionLocal() check belongs inside aliasErrno(). This will repeat the getUnderlyingObject() call, but from a quick test (with this commit: https://github.com/llvm/llvm-project/commit/60cab1e6058303a41a361f12ddf3c3ab4649bae5) this doesn't seem to affect compile-time, so I think it's fine.

https://github.com/llvm/llvm-project/pull/157495