heap: Fix variable shadowing when using TRACE_GC() macro

Introduce IDENTIFIER_WITH_LINE() that can be similarly used in other
scope-based macros throughout the codebase.

Bug: v8:12244,v8:12245
Change-Id: If9d45b7065d7eb3df0297f35eb9be777b497ea95
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3181524
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77038}

src/base/macros.h

@@ -18,6 +18,11 @@
 // This macro does nothing. That's all.
 #define NOTHING(...)
 
+#define CONCAT_(a, b) a##b
+#define CONCAT(a, b) CONCAT_(a, b)
+// Creates an unique identifier. Useful for scopes to avoid shadowing names.
+#define UNIQUE_IDENTIFIER(base) CONCAT(base, __COUNTER__)
+
 // TODO(all) Replace all uses of this macro with C++'s offsetof. To do that, we
 // have to make sure that only standard-layout types and simple field
 // designators are used.

src/heap/gc-tracer.h

@@ -7,6 +7,7 @@
 
 #include "include/v8-metrics.h"
 #include "src/base/compiler-specific.h"
+#include "src/base/macros.h"
 #include "src/base/optional.h"
 #include "src/base/platform/platform.h"
 #include "src/base/platform/time.h"
@@ -32,22 +33,23 @@ enum ScavengeSpeedMode { kForAllObjects, kForSurvivedObjects };
   "devtools.timeline," TRACE_DISABLED_BY_DEFAULT("v8.gc")
 
 #define TRACE_GC(tracer, scope_id)                                    \
-  GCTracer::Scope::ScopeId gc_tracer_scope_id(scope_id);      \
-  GCTracer::Scope gc_tracer_scope(tracer, gc_tracer_scope_id, \
-                                  ThreadKind::kMain);         \
-  TRACE_EVENT0(TRACE_GC_CATEGORIES, GCTracer::Scope::Name(gc_tracer_scope_id))
+  GCTracer::Scope UNIQUE_IDENTIFIER(gc_tracer_scope)(                 \
+      tracer, GCTracer::Scope::ScopeId(scope_id), ThreadKind::kMain); \
+  TRACE_EVENT0(TRACE_GC_CATEGORIES,                                   \
+               GCTracer::Scope::Name(GCTracer::Scope::ScopeId(scope_id)))
 
 #define TRACE_GC1(tracer, scope_id, thread_kind)                \
-  GCTracer::Scope::ScopeId gc_tracer_scope_id(scope_id);                    \
-  GCTracer::Scope gc_tracer_scope(tracer, gc_tracer_scope_id, thread_kind); \
-  TRACE_EVENT0(TRACE_GC_CATEGORIES, GCTracer::Scope::Name(gc_tracer_scope_id))
+  GCTracer::Scope UNIQUE_IDENTIFIER(gc_tracer_scope)(           \
+      tracer, GCTracer::Scope::ScopeId(scope_id), thread_kind); \
+  TRACE_EVENT0(TRACE_GC_CATEGORIES,                             \
+               GCTracer::Scope::Name(GCTracer::Scope::ScopeId(scope_id)))
 
 #define TRACE_GC_EPOCH(tracer, scope_id, thread_kind)                     \
-  GCTracer::Scope::ScopeId gc_tracer_scope_id(scope_id);                       \
-  GCTracer::Scope gc_tracer_scope(tracer, gc_tracer_scope_id, thread_kind);    \
-  CollectionEpoch gc_tracer_epoch = tracer->CurrentEpoch(scope_id);            \
-  TRACE_EVENT1(TRACE_GC_CATEGORIES, GCTracer::Scope::Name(gc_tracer_scope_id), \
-               "epoch", gc_tracer_epoch)
+  GCTracer::Scope UNIQUE_IDENTIFIER(gc_tracer_scope)(                     \
+      tracer, GCTracer::Scope::ScopeId(scope_id), thread_kind);           \
+  TRACE_EVENT1(TRACE_GC_CATEGORIES,                                       \
+               GCTracer::Scope::Name(GCTracer::Scope::ScopeId(scope_id)), \
+               "epoch", tracer->CurrentEpoch(scope_id))
 
 // GCTracer collects and prints ONE line after each garbage collector
 // invocation IFF --trace_gc is used.