[ptr-compr][arm64] Add a switch for branchless/branchful decompression

Similar to x64's https://chromium-review.googlesource.com/c/v8/v8/+/1511486

Bug: v8:7703
Change-Id: Ifd634a36bb56a53cb9901d9dd0899b66229607ef
Cq-Include-Trybots: luci.v8.try:v8_linux64_arm64_pointer_compression_rel_ng
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1535828
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Auto-Submit: Santiago Aboy Solanes <solanes@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60412}

src/arm64/macro-assembler-arm64.cc

@@ -2830,8 +2830,9 @@ void TurboAssembler::DecompressTaggedPointer(const Register& destination,
 void TurboAssembler::DecompressAnyTagged(const Register& destination,
                                          const MemOperand& field_operand) {
   RecordComment("[ DecompressAnyTagged");
-  UseScratchRegisterScope temps(this);
   Ldrsw(destination, field_operand);
+  if (kUseBranchlessPtrDecompression) {
+    UseScratchRegisterScope temps(this);
     // Branchlessly compute |masked_root|:
     // masked_root = HAS_SMI_TAG(destination) ? 0 : kRootRegister;
     STATIC_ASSERT((kSmiTagSize == 1) && (kSmiTag == 0));
@@ -2839,9 +2840,15 @@ void TurboAssembler::DecompressAnyTagged(const Register& destination,
     // Sign extend tag bit to entire register.
     Sbfx(masked_root, destination, 0, kSmiTagSize);
     And(masked_root, masked_root, kRootRegister);
-  // Now this add operation will either leave the value unchanged if it is a smi
-  // or add the isolate root if it is a heap object.
+    // Now this add operation will either leave the value unchanged if it is a
+    // smi or add the isolate root if it is a heap object.
     Add(destination, masked_root, destination);
+  } else {
+    Label done;
+    JumpIfSmi(destination, &done);
+    Add(destination, kRootRegister, destination);
+    bind(&done);
+  }
   RecordComment("]");
 }