[cleanup] Make RelocInfo::NONE have value 0

The {NONE} reloc info is the one used most often, i.e. for every
assembler call that takes an {Immediate} on x64 which is not
relocatable.
Hence assign value 0 to {NONE} such that constructing such immediates is
faster and also checking for this most common case is faster.

R=ishell@chromium.org

Bug: v8:10576
Change-Id: I3c048710b80dd31fa5b5d3b1415d72a24d95cb90
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2237136Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68259}

src/codegen/reloc-info.h

@@ -54,6 +54,8 @@ class RelocInfo {
     // Please note the order is important (see IsRealRelocMode, IsGCRelocMode,
     // and IsShareableRelocMode predicates below).
 
+    NONE,  // Never recorded value. Most common one, hence value 0.
+
     CODE_TARGET,
     RELATIVE_CODE_TARGET,  // LAST_CODE_TARGET_MODE
     COMPRESSED_EMBEDDED_OBJECT,
@@ -89,7 +91,6 @@ class RelocInfo {
 
     // Pseudo-types
     NUMBER_OF_MODES,
-    NONE,  // never recorded value
 
     LAST_CODE_TARGET_MODE = RELATIVE_CODE_TARGET,
     FIRST_REAL_RELOC_MODE = CODE_TARGET,
@@ -123,10 +124,8 @@ class RelocInfo {
     return mode <= LAST_GCED_ENUM;
   }
   static constexpr bool IsShareableRelocMode(Mode mode) {
-    static_assert(RelocInfo::NONE >= RelocInfo::FIRST_SHAREABLE_RELOC_MODE,
-                  "Users of this function rely on NONE being a sharable "
-                  "relocation mode.");
-    return mode >= RelocInfo::FIRST_SHAREABLE_RELOC_MODE;
+    return mode == RelocInfo::NONE ||
+           mode >= RelocInfo::FIRST_SHAREABLE_RELOC_MODE;
   }
   static constexpr bool IsCodeTarget(Mode mode) { return mode == CODE_TARGET; }
   static constexpr bool IsCodeTargetMode(Mode mode) {

src/codegen/x64/macro-assembler-x64.h

@@ -443,7 +443,7 @@ class V8_EXPORT_PRIVATE TurboAssembler : public TurboAssemblerBase {
   void Move(Register dst, Address ptr, RelocInfo::Mode rmode) {
     // This method must not be used with heap object references. The stored
     // address is not GC safe. Use the handle version instead.
-    DCHECK(rmode > RelocInfo::LAST_GCED_ENUM);
+    DCHECK(rmode == RelocInfo::NONE || rmode > RelocInfo::LAST_GCED_ENUM);
     movq(dst, Immediate64(ptr, rmode));
   }
 

src/objects/code.cc

@@ -239,7 +239,8 @@ const char* AbstractCode::Kind2String(Kind kind) {
 
 bool Code::IsIsolateIndependent(Isolate* isolate) {
   constexpr int all_real_modes_mask =
-      (1 << (RelocInfo::LAST_REAL_RELOC_MODE + 1)) - 1;
+      (1 << (RelocInfo::LAST_REAL_RELOC_MODE + 1)) -
+      (1 << (RelocInfo::FIRST_REAL_RELOC_MODE - 1)) - 1;
   constexpr int mode_mask = all_real_modes_mask &
                             ~RelocInfo::ModeMask(RelocInfo::CONST_POOL) &
                             ~RelocInfo::ModeMask(RelocInfo::OFF_HEAP_TARGET) &