[llvm] [BasicAA][TLI] Treat local-linkage globals or known environments as not aliasing errno (PR #170290)

[Antonio Frighetto via llvm-commits]

================
@@ -1862,16 +1862,31 @@ AliasResult BasicAAResult::aliasCheckRecursive(
 }
 
 AliasResult BasicAAResult::aliasErrno(const MemoryLocation &Loc,
-                                      const Module *M) {
+                                      const CallBase *Call) {
   // There cannot be any alias with errno if the given memory location is an
   // identified function-local object, or the size of the memory access is
   // larger than the integer size.
   if (Loc.Size.hasValue() &&
       Loc.Size.getValue().getKnownMinValue() * 8 > TLI.getIntSize())
     return AliasResult::NoAlias;
 
-  if (isIdentifiedFunctionLocal(getUnderlyingObject(Loc.Ptr)))
+  const Value *Object = getUnderlyingObject(Loc.Ptr);
+  if (isIdentifiedFunctionLocal(Object))
     return AliasResult::NoAlias;
+
+  if (auto *GV = dyn_cast<GlobalVariable>(Object)) {
+    // Errno cannot alias internal/private globals.
+    if (GV->hasLocalLinkage())
----------------
antoniofrighetto wrote:

Moved on top. I'm not completely sure under which conditions this could happen (in LTO), but I think it makes sense (also refined the comment, please see if that confirms my understanding).

https://github.com/llvm/llvm-project/pull/170290