[Flags] Add a warning when flags are disabled due to conflicts.

Change-Id: I29b3a805a6031bf874e8b7e0775f5725b6180fca
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2914879Reviewed-by: Mythri Alle <mythria@chromium.org>
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74734}

src/init/v8.cc

@@ -65,6 +65,13 @@ void V8::TearDown() {
   FlagList::ResetAllFlags();  // Frees memory held by string arguments.
 }
 
+#define DISABLE_FLAG(flag)                                                    \
+  if (FLAG_##flag) {                                                          \
+    PrintF(stderr,                                                            \
+           "Warning: disabling flag --" #flag " due to conflicting flags\n"); \
+    FLAG_##flag = false;                                                      \
+  }
+
 void V8::InitializeOncePerProcessImpl() {
   // Update logging information before enforcing flag implications.
   bool* log_all_flags[] = {&FLAG_turbo_profiling_log_builtins,
@@ -129,7 +136,7 @@ void V8::InitializeOncePerProcessImpl() {
   // memory.
 #if V8_ENABLE_WEBASSEMBLY
   if (FLAG_jitless && !FLAG_correctness_fuzzer_suppressions) {
-    FLAG_expose_wasm = false;
+    DISABLE_FLAG(expose_wasm);
   }
 #endif
 
@@ -139,24 +146,24 @@ void V8::InitializeOncePerProcessImpl() {
   // TODO(chromium:1205289): Teach relevant fuzzers to not pass TF tracing
   // flags instead, and remove this section.
   if (FLAG_fuzzing && FLAG_concurrent_recompilation) {
-    FLAG_trace_turbo = false;
-    FLAG_trace_turbo_graph = false;
-    FLAG_trace_turbo_scheduled = false;
-    FLAG_trace_turbo_reduction = false;
-    FLAG_trace_turbo_trimming = false;
-    FLAG_trace_turbo_jt = false;
-    FLAG_trace_turbo_ceq = false;
-    FLAG_trace_turbo_loop = false;
-    FLAG_trace_turbo_alloc = false;
-    FLAG_trace_all_uses = false;
-    FLAG_trace_representation = false;
-    FLAG_trace_turbo_stack_accesses = false;
+    DISABLE_FLAG(trace_turbo);
+    DISABLE_FLAG(trace_turbo_graph);
+    DISABLE_FLAG(trace_turbo_scheduled);
+    DISABLE_FLAG(trace_turbo_reduction);
+    DISABLE_FLAG(trace_turbo_trimming);
+    DISABLE_FLAG(trace_turbo_jt);
+    DISABLE_FLAG(trace_turbo_ceq);
+    DISABLE_FLAG(trace_turbo_loop);
+    DISABLE_FLAG(trace_turbo_alloc);
+    DISABLE_FLAG(trace_all_uses);
+    DISABLE_FLAG(trace_representation);
+    DISABLE_FLAG(trace_turbo_stack_accesses);
   }
 
   if (FLAG_regexp_interpret_all && FLAG_regexp_tier_up) {
     // Turning off the tier-up strategy, because the --regexp-interpret-all and
     // --regexp-tier-up flags are incompatible.
-    FLAG_regexp_tier_up = false;
+    DISABLE_FLAG(regexp_tier_up);
   }
 
   // The --jitless and --interpreted-frames-native-stack flags are incompatible