[clang] [analyzer] Use AllocaRegion in MallocChecker (PR #72402)

[via cfe-commits]

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@@ -266,13 +266,18 @@ void CheckUseZeroAllocated1(void) {
 }
 
 char CheckUseZeroAllocated2(void) {
+  // FIXME: The return value of `alloca()` is modeled with `AllocaRegion`
+  // instead of `SymbolicRegion`, so the current implementation of
+  // `MallocChecker::checkUseZeroAllocated()` cannot handle it; and we get an
+  // unrelated, but suitable warning from core.uninitialized.UndefReturn.
   char *p = alloca(0);
-  return *p; // expected-warning {{Use of memory allocated with size zero}}
+  return *p; // expected-warning {{Undefined or garbage value returned to caller}}
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DonatNagyE wrote:

Also note that the report "Use of memory allocated with size zero" is redundant with ArrayBoundV2, which detects and reports that the offset (0) is not smaller than the extent (also 0). Based on this I'm not sure that it's useful to maintain this "size zero" special case.

https://github.com/llvm/llvm-project/pull/72402