[TSan, SanitizerBinaryMetadata] Analyze the capture status for alloca rather than arbitrary Addr

This commit addresses the limitation in `PointerMayBeCaptured` analysis
when dealing with derived pointers (e.g. arr+1) as described in
issue #132739.

The current implementation may miss captures of the underlying alloca
when analyzing derived pointers. Even when working correctly,
backtracking to the original alloca during analysis causes redundancy
to the outer's `findAllocaForValue`.

Key changes:
Directly analyze the capture status of the underlying alloca instead
   of derived pointers to ensure accurate capture detection

This patch fixes some FNs of TSan, referring to the appending
testcases for more details.

Author: Camsyn

compiler-rt/test/tsan/stack_race3.cpp

@@ -0,0 +1,22 @@
+// RUN: %clangxx_tsan -O1 %s -o %t && %deflake %run %t | FileCheck %s
+#include "test.h"
+
+void *Thread(void *a) {
+  barrier_wait(&barrier);
+  ((int*)a)[1] = 43;
+  return 0;
+}
+
+int main() {
+  barrier_init(&barrier, 2);
+  int Arr[2] = {41, 42};
+  pthread_t t;
+  pthread_create(&t, 0, Thread, &Arr[0]);
+  Arr[1] = 43;
+  barrier_wait(&barrier);
+  pthread_join(t, 0);
+}
+
+// CHECK: WARNING: ThreadSanitizer: data race
+// CHECK:   Location is stack of main thread.
+

llvm/lib/Transforms/Instrumentation/SanitizerBinaryMetadata.cpp

@@ -394,7 +394,7 @@ bool maybeSharedMutable(const Value *Addr) {
     return true;
 
   const AllocaInst *AI = findAllocaForValue(Addr);
-  if (AI && !PointerMayBeCaptured(Addr, /*ReturnCaptures=*/true))
+  if (AI && !PointerMayBeCaptured(AI, /*ReturnCaptures=*/true))
     return false; // Object is on stack but does not escape.
 
   Addr = Addr->stripInBoundsOffsets();

llvm/lib/Transforms/Instrumentation/ThreadSanitizer.cpp

@@ -449,7 +449,8 @@ void ThreadSanitizer::chooseInstructionsToInstrument(
     }
 
     const AllocaInst *AI = findAllocaForValue(Addr);
-    if (AI && !PointerMayBeCaptured(Addr, /*ReturnCaptures=*/true)) {
+    // Instead of Addr, we should check whether its base pointer is captured.
+    if (AI && !PointerMayBeCaptured(AI, /*ReturnCaptures=*/true)) {
       // The variable is addressable but not captured, so it cannot be
       // referenced from a different thread and participate in a data race
       // (see llvm/Analysis/CaptureTracking.h for details).