[clang] [llvm] [clang][CodeGen][AA] Introduce `!llvm.errno.tbaa` for errno alias disambiguation (PR #125258)

[Nikita Popov via cfe-commits]

================
@@ -970,6 +971,19 @@ ModRefInfo BasicAAResult::getModRefInfo(const CallBase 
*Call,
   }
 
   ModRefInfo Result = ArgMR | OtherMR;
+
+  // Refine writes to errno memory. We can safely exclude the errno location if
+  // the given memory location is an alloca, the size of the memory access is
+  // larger than `sizeof(int)` or if TBAA proves it does not alias errno.
+  if ((ErrnoMR | OtherMR) != OtherMR) {
+    bool IsLocSizeUnknown = Loc.Size == MemoryLocation::UnknownSize;
----------------
nikic wrote:

Should check `!Loc.Size.hasValue()`. There are multiple types of unknown sizes.

https://github.com/llvm/llvm-project/pull/125258
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