[ VM / Testing ] Add build flags to enable code coverage

Change-Id: I37e945f842932b1ac1d87444e4fec2eb752f312f
Reviewed-on: https://dart-review.googlesource.com/c/79465
Commit-Queue: Ben Konyi <bkonyi@google.com>
Reviewed-by: Zach Anderson <zra@google.com>
Auto-Submit: Ben Konyi <bkonyi@google.com>

runtime/BUILD.gn

@@ -165,13 +165,20 @@ config("dart_config") {
       "-fno-exceptions",
     ]
 
-    if (dart_debug) {
+    ldflags = []
+    if (is_clang && dart_vm_code_coverage) {
+      cflags += [
+        "-O0",
+        "-fprofile-arcs",
+        "-ftest-coverage",
+      ]
+      ldflags += [ "--coverage" ]
+    } else if (dart_debug) {
       cflags += [ "-O${dart_debug_optimization_level}" ]
     } else {
       cflags += [ "-O3" ]
     }
 
-    ldflags = []
     if (defined(is_asan) && is_asan) {
       ldflags += [ "-fsanitize=address" ]
     }

runtime/runtime_args.gni

@@ -31,9 +31,13 @@ declare_args() {
   # Available options are: arm, arm64, x64, ia32, and dbc.
   dart_target_arch = target_cpu
 
-  # The optimization level to use for debug builds.
+  # The optimization level to use for debug builds. Defaults to 0 for builds with
+  # code coverage enabled.
   dart_debug_optimization_level = "2"
 
+  # Whether to enable code coverage for the standalone VM.
+  dart_vm_code_coverage = false
+
   # Whether to fall back to built-in root certificates when they cannot be
   # verified at the operating system level.
   dart_use_fallback_root_certificates = false

tools/gn.py

@@ -230,6 +230,9 @@ def ToGnArgs(args, mode, arch, target_os):
                                       gn_args['target_cpu'])
   gn_args['is_clang'] = args.clang and not dont_use_clang
 
+  enable_code_coverage = args.code_coverage and gn_args['is_clang']
+  gn_args['dart_vm_code_coverage'] = enable_code_coverage
+
   gn_args['is_asan'] = args.asan and gn_args['is_clang']
   gn_args['is_msan'] = args.msan and gn_args['is_clang']
   gn_args['is_tsan'] = args.tsan and gn_args['is_clang']
@@ -262,7 +265,11 @@ def ToGnArgs(args, mode, arch, target_os):
     gn_args['use_goma'] = False
     gn_args['goma_dir'] = None
 
-  if args.debug_opt_level:
+  # Code coverage requires -O0 to be set.
+  if enable_code_coverage:
+    gn_args['dart_debug_optimization_level'] = 0
+    gn_args['debug_optimization_level'] = 0
+  elif args.debug_opt_level:
     gn_args['dart_debug_optimization_level'] = args.debug_opt_level
     gn_args['debug_optimization_level'] = args.debug_opt_level
 
@@ -384,6 +391,11 @@ def parse_args(args):
       help='Disable Clang',
       dest='clang',
       action='store_false')
+  other_group.add_argument('--code-coverage',
+      help='Enable code coverage for the standalone VM',
+      default=False,
+      dest="code_coverage",
+      action='store_true')
   other_group.add_argument('--debug-opt-level',
       '-d',
       help='The optimization level to use for debug builds',