[clang] Thread Safety Analysis: Very basic capability alias-analysis (PR #142955)

[Marco Elver via cfe-commits]

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@@ -1012,6 +1030,107 @@ void SExprBuilder::exitCFG(const CFGBlock *Last) {
   IncompleteArgs.clear();
 }
 
+bool SExprBuilder::isVariableReassigned(const VarDecl *VD) {
+  // Note: The search is performed lazily per-variable and result is cached. An
+  // alternative would have been to eagerly create a set of all reassigned
+  // variables, but that would consume significantly more memory. The number of
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melver wrote:

I spoke too soon.

I might have found a way to use `LocalVariableMap`, and inject it into SExprBuilder in the right place. The tests pass and it appears to deal with e.g.

```
+void testBasicPointerAliasNoInit(Foo *f) {
+  Foo *ptr;
+
+  ptr = f;
+  ptr->mu.Lock();
+  f->data = 42;
+  ptr->mu.Unlock();
+}
+
```

Still trying to understand if this is actually sound, but if it is, this is far more powerful than before.

https://github.com/llvm/llvm-project/pull/142955