Restore -fno-delete-null-pointer-checks

The commit https://chromium-review.googlesource.com/c/chromium/src/+/1294449
removed this in an apparent brainfart when it was first moved from gcc to clang,
then removed from the patch alltogether.

This exposed an issue with a nullptr check in logging that has been fixed.

Task-number: QTBUG-77671
Change-Id: I59677ed997da4278c01676b01950c0ea03c67126
Reviewed-by: Jüri Valdmann <juri.valdmann@qt.io>
(cherry picked from commit 32e459f495dc0475cdc1703514a257b45ccd3d84)
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

3 files changed, 24 insertions, 5 deletions

diff --git a/chromium/base/trace_event/category_registry.h b/chromium/base/trace_event/category_registry.h
index a6439d94595..a2bdb2c8b29 100644
--- a/chromium/base/trace_event/category_registry.h
+++ b/chromium/base/trace_event/category_registry.h
@@ -83,6 +83,21 @@ class BASE_EXPORT CategoryRegistry {
 #endif
   }
 
+  static constexpr const unsigned char* GetBuiltinCategoryEnabled(
+      const char* category_group) {
+#if defined(OS_WIN) && defined(COMPONENT_BUILD)
+    // The address cannot be evaluated at compile-time in Windows compoment
+    // builds.
+    return nullptr;
+#else
+    for (size_t i = 0; i < BuiltinCategories::Size(); ++i) {
+      if (StrEqConstexpr(category_group, BuiltinCategories::At(i)))
+        return categories_[i].state_ptr();
+    }
+    return nullptr;
+#endif
+  }
+
   // Returns whether |category| points at one of the meta categories that
   // shouldn't be displayed in the tracing UI.
   static bool IsMetaCategory(const TraceCategory* category);
diff --git a/chromium/base/trace_event/trace_log.h b/chromium/base/trace_event/trace_log.h
index e0c850ca41e..4814893c84c 100644
--- a/chromium/base/trace_event/trace_log.h
+++ b/chromium/base/trace_event/trace_log.h
@@ -221,11 +221,7 @@ class BASE_EXPORT TraceLog : public MemoryDumpProvider {
       const unsigned char* category_group_enabled);
   static constexpr const unsigned char* GetBuiltinCategoryEnabled(
       const char* name) {
-    TraceCategory* builtin_category =
-        CategoryRegistry::GetBuiltinCategoryByName(name);
-    if (builtin_category)
-      return builtin_category->state_ptr();
-    return nullptr;
+    return CategoryRegistry::GetBuiltinCategoryEnabled(name);
   }
 
   // Called by TRACE_EVENT* macros, don't call this directly.
diff --git a/chromium/build/config/compiler/BUILD.gn b/chromium/build/config/compiler/BUILD.gn
index ae972412e91..ab47e2b98f8 100644
--- a/chromium/build/config/compiler/BUILD.gn
+++ b/chromium/build/config/compiler/BUILD.gn
@@ -1475,6 +1475,14 @@ config("default_warnings") {
       cflags += [ "-Wno-maybe-uninitialized" ]
       cflags += [ "-Wno-deprecated-declarations" ]
 
+      # GCC assumes 'this' is never nullptr and optimizes away code
+      # like "if (this == nullptr) ...": [1].  However, some Chromium
+      # code relies on these types of null pointer checks [2], so
+      # disable this optimization.
+      # [1] https://gcc.gnu.org/gcc-6/porting_to.html#this-cannot-be-null
+      # [2] https://crbug.com/784492#c13
+      cflags += [ "-fno-delete-null-pointer-checks" ]
+
       # -Wcomment gives too many false positives in the case a
       # backslash ended comment line is followed by a new line of
       # comments