cppgc: Remove conservative stack scan guard

Supported HW architectures:
ia32, x64, arm, arm64, ppc64, s390, mips, mips64

Compiler support:
- clang/gcc: all
- msvc tools: ia32, x64, arm64

Thanks all for porting!

Bug: chromium:1056170
Change-Id: I26ea7d727dc6d90929941668b8f115bdbaf226ab
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2153210
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67203}

BUILD.gn

@@ -351,21 +351,7 @@ config("libbase_config") {
 
 # This config should be applied to code using the cppgc_base.
 config("cppgc_base_config") {
-  # Assume is_clang = false means GCC or other compilers that are compatible
-  # with gas inline assembly on non-Windows builds. Cross builds for
-  # Linux->Windows are covered as they use clang.
   defines = []
-  if (is_clang || !is_win) {
-    if (target_cpu == "x64" || target_cpu == "x86" || target_cpu == "arm" ||
-        target_cpu == "arm64" || target_cpu == "ppc64" ||
-        target_cpu == "s390x" || target_cpu == "mipsel" ||
-        target_cpu == "mips64el") {
-      defines += [ "CPPGC_SUPPORTS_CONSERVATIVE_STACK_SCAN" ]
-    }
-  } else if (is_win) {
-    # Assume that non-clang builds on Windows use native tools.
-    defines += [ "CPPGC_SUPPORTS_CONSERVATIVE_STACK_SCAN" ]
-  }
   if (cppgc_enable_object_names) {
     defines += [ "CPPGC_SUPPORTS_OBJECT_NAMES" ]
   }

src/heap/cppgc/stack.cc

@@ -63,8 +63,6 @@ void IterateAsanFakeFrameIfNecessary(StackVisitor* visitor,
 
 #endif  // V8_USE_ADDRESS_SANITIZER
 
-#ifdef CPPGC_SUPPORTS_CONSERVATIVE_STACK_SCAN
-
 void IterateSafeStackIfNecessary(StackVisitor* visitor) {
 #if defined(__has_feature)
 #if __has_feature(safe_stack)
@@ -118,19 +116,13 @@ void IteratePointersImpl(const Stack* stack, StackVisitor* visitor,
   }
 }
 
-#endif  // CPPGC_SUPPORTS_CONSERVATIVE_STACK_SCAN
-
 }  // namespace
 
 void Stack::IteratePointers(StackVisitor* visitor) const {
-#ifdef CPPGC_SUPPORTS_CONSERVATIVE_STACK_SCAN
   PushAllRegistersAndIterateStack(this, visitor, &IteratePointersImpl);
   // No need to deal with callee-saved registers as they will be kept alive by
   // the regular conservative stack iteration.
   IterateSafeStackIfNecessary(visitor);
-#else   // !CPPGC_SUPPORTS_CONSERVATIVE_STACK_SCAN
-  FATAL("Conservative stack scan not supported on current platform.");
-#endif  // !CPPGC_SUPPORTS_CONSERVATIVE_STACK_SCAN
 }
 
 }  // namespace internal

test/unittests/heap/cppgc/heap_unittest.cc

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifdef CPPGC_SUPPORTS_CONSERVATIVE_STACK_SCAN
-
 #include "src/heap/cppgc/heap.h"
 #include "include/cppgc/allocation.h"
 #include "test/unittests/heap/cppgc/tests.h"
@@ -72,5 +70,3 @@ TEST_F(GCHeapTest, ConservaitveGCRetainsObjectOnStack) {
 
 }  // namespace internal
 }  // namespace cppgc
-
-#endif  // CPPGC_SUPPORTS_CONSERVATIVE_STACK_SCAN

test/unittests/heap/cppgc/stack_unittest.cc

@@ -46,8 +46,6 @@ TEST_F(GCStackTest, IsOnStackForHeapValue) {
   EXPECT_FALSE(GetStack()->IsOnStack(dummy.get()));
 }
 
-#ifdef CPPGC_SUPPORTS_CONSERVATIVE_STACK_SCAN
-
 namespace {
 
 class StackScanner final : public StackVisitor {
@@ -355,7 +353,5 @@ TEST_F(GCStackTest, StackAlignment) {
 }
 #endif  // V8_OS_LINUX && (V8_HOST_ARCH_IA32 || V8_HOST_ARCH_X64)
 
-#endif  // CPPGC_SUPPORTS_CONSERVATIVE_STACK_SCAN
-
 }  // namespace internal
 }  // namespace cppgc