[compiler-rt] [sanitizer] avoid UB in allocator (#126977)

fmayer · web-flow · commit 6936fadfc320 · 2025-02-12T15:49:55.000-08:00
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_allocator_local_cache.h b/compiler-rt/lib/sanitizer_common/sanitizer_allocator_local_cache.h
@@ -166,7 +166,7 @@ struct SizeClassAllocator32LocalCache {
       DCHECK_GT(c->count, 0);
     }
     void *res = c->batch[--c->count];
-    PREFETCH(c->batch[c->count - 1]);
+    PREFETCH(c->batch[c->count > 0 ? c->count - 1 : 0]);
     stats_.Add(AllocatorStatAllocated, c->class_size);
     return res;
   }

Original file line number	Diff line number	Diff line change
`@@ -166,7 +166,7 @@ struct SizeClassAllocator32LocalCache {`
`166`	`166`	`DCHECK_GT(c->count, 0);`
`167`	`167`	`}`
`168`	`168`	`void *res = c->batch[--c->count];`
`169`		`- PREFETCH(c->batch[c->count - 1]);`
	`169`	`+ PREFETCH(c->batch[c->count > 0 ? c->count - 1 : 0]);`
`170`	`170`	`stats_.Add(AllocatorStatAllocated, c->class_size);`
`171`	`171`	`return res;`
`172`	`172`	`}`