[ptr-compr] Add gn arg for 31bit Smis on 64bit arch

Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: I44e62d53bc7b341a685eeca5691a86e915fcce44
Bug: v8:8344
Reviewed-on: https://chromium-review.googlesource.com/c/1292064Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56940}

BUILD.gn

@@ -92,6 +92,7 @@ declare_args() {
 
   # Enable pointer compression (sets -dV8_COMPRESS_POINTERS).
   v8_enable_pointer_compression = false
+  v8_enable_31bit_smis_on_64bit_arch = false
 
   # Interpreted regexp engine exists as platform-independent alternative
   # based where the regular expression is compiled to a bytecode.
@@ -340,6 +341,9 @@ config("features") {
   if (v8_enable_pointer_compression) {
     defines += [ "V8_COMPRESS_POINTERS" ]
   }
+  if (v8_enable_31bit_smis_on_64bit_arch) {
+    defines += [ "V8_31BIT_SMIS_ON_64BIT_ARCH" ]
+  }
   if (v8_enable_object_print) {
     defines += [ "OBJECT_PRINT" ]
   }

include/OWNERS

@@ -5,6 +5,7 @@ danno@chromium.org
 ulan@chromium.org
 yangguo@chromium.org
 
+per-file v8-internal.h=file://OWNERS
 per-file v8-inspector.h=dgozman@chromium.org
 per-file v8-inspector.h=pfeldman@chromium.org
 per-file v8-inspector.h=kozyatinskiy@chromium.org

include/v8-internal.h

@@ -103,7 +103,7 @@ struct SmiTagging<8> {
   }
 };
 
-#if V8_COMPRESS_POINTERS
+#if defined(V8_COMPRESS_POINTERS) || defined(V8_31BIT_SMIS_ON_64BIT_ARCH)
 static_assert(
     kApiPointerSize == kApiInt64Size,
     "Pointer compression can be enabled only for 64-bit architectures");