Revert "[arm64] Increase code alignment to 64"

This reverts commit 319e747a.

Reason for revert: it brought unexpected performance regressions.

Original change's description:
> [arm64] Increase code alignment to 64
>
> This should fix unexpected regressions which occur after builtins
> modifications.
>
> This CL affects alignment of embedded builtins on all configurations
> and Code header size only for non-pointer compression configuration.
>
> Bug: v8:11708
> Change-Id: I8058197c5b768a699e7f52446424013e86203b57
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3700392
> Commit-Queue: Igor Sheludko <ishell@chromium.org>
> Reviewed-by: Leszek Swirski <leszeks@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#81113}

Bug: v8:11708
Change-Id: I238e799284d59e80dee244b240fe2a72c33e83b0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3716485
Auto-Submit: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#81292}

src/common/globals.h

@@ -649,7 +649,7 @@ constexpr intptr_t kDoubleAlignmentMask = kDoubleAlignment - 1;
 // Desired alignment for generated code is 64 bytes on x64 (to allow 64-bytes
 // loop header alignment) and 32 bytes (to improve cache line utilization) on
 // other architectures.
-#if V8_TARGET_ARCH_X64 || V8_TARGET_ARCH_ARM64
+#if V8_TARGET_ARCH_X64
 constexpr int kCodeAlignmentBits = 6;
 #elif V8_TARGET_ARCH_PPC64
 // 64 byte alignment is needed on ppc64 to make sure p10 prefixed instructions

src/objects/code.h

@@ -668,7 +668,7 @@ class Code : public HeapObject {
   // due to padding for code alignment.
 #if V8_TARGET_ARCH_ARM64
   static constexpr int kHeaderPaddingSize =
-      V8_EXTERNAL_CODE_SPACE_BOOL ? 4 : (COMPRESS_POINTERS_BOOL ? 8 : 52);
+      V8_EXTERNAL_CODE_SPACE_BOOL ? 4 : (COMPRESS_POINTERS_BOOL ? 8 : 20);
 #elif V8_TARGET_ARCH_MIPS64
   static constexpr int kHeaderPaddingSize = 20;
 #elif V8_TARGET_ARCH_LOONG64

src/snapshot/embedded/platform-embedded-file-writer-aix.cc

@@ -53,7 +53,7 @@ void PlatformEmbeddedFileWriterAIX::DeclareSymbolGlobal(const char* name) {
 }
 
 void PlatformEmbeddedFileWriterAIX::AlignToCodeAlignment() {
-#if V8_TARGET_ARCH_X64 || V8_TARGET_ARCH_ARM64
+#if V8_TARGET_ARCH_X64
   // On x64 use 64-bytes code alignment to allow 64-bytes loop header alignment.
   static_assert((1 << 6) >= kCodeAlignment);
   fprintf(fp_, ".align 6\n");

src/snapshot/embedded/platform-embedded-file-writer-generic.cc

@@ -67,7 +67,7 @@ void PlatformEmbeddedFileWriterGeneric::AlignToCodeAlignment() {
   // On these architectures and platforms, we remap the builtins, so need these
   // to be aligned on a page boundary.
   fprintf(fp_, ".balign 4096\n");
-#elif V8_TARGET_ARCH_X64 || V8_TARGET_ARCH_ARM64
+#elif V8_TARGET_ARCH_X64
   // On x64 use 64-bytes code alignment to allow 64-bytes loop header alignment.
   static_assert(64 >= kCodeAlignment);
   fprintf(fp_, ".balign 64\n");

src/snapshot/embedded/platform-embedded-file-writer-win.cc

@@ -609,7 +609,7 @@ void PlatformEmbeddedFileWriterWin::DeclareSymbolGlobal(const char* name) {
 }
 
 void PlatformEmbeddedFileWriterWin::AlignToCodeAlignment() {
-#if V8_TARGET_ARCH_X64 || V8_TARGET_ARCH_ARM64
+#if V8_TARGET_ARCH_X64
   // On x64 use 64-bytes code alignment to allow 64-bytes loop header alignment.
   static_assert(64 >= kCodeAlignment);
   fprintf(fp_, ".balign 64\n");