[Turbofan][ptr-compr][x64] Use kScratchRegister instead of a fresh one

... for decompression because the former is not used by register
allocator and therefore always available.

Bug: v8:7703
Change-Id: I72d738be69c339444311d75c69f04c104e90bb90
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1533857Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60390}

src/compiler/backend/x64/code-generator-x64.cc

@@ -1937,8 +1937,7 @@ CodeGenerator::CodeGenResult CodeGenerator::AssembleArchInstruction(
     }
     case kX64MovqDecompressAnyTagged: {
       CHECK(instr->HasOutput());
-      __ DecompressAnyTagged(i.OutputRegister(), i.MemoryOperand(),
-                             i.TempRegister(0));
+      __ DecompressAnyTagged(i.OutputRegister(), i.MemoryOperand());
       break;
     }
     case kX64MovqCompressTagged: {

src/compiler/backend/x64/instruction-selector-x64.cc

@@ -351,12 +351,6 @@ void InstructionSelector::VisitLoad(Node* node) {
   X64OperandGenerator g(this);
 
   ArchOpcode opcode = GetLoadOpcode(load_rep);
-  size_t temp_count = 0;
-  InstructionOperand temps[1];
-  if (COMPRESS_POINTERS_BOOL && opcode == kX64MovqDecompressAnyTagged) {
-    temps[temp_count++] = g.TempRegister();
-  }
-  DCHECK_LE(temp_count, arraysize(temps));
   InstructionOperand outputs[] = {g.DefineAsRegister(node)};
   InstructionOperand inputs[3];
   size_t input_count = 0;
@@ -369,7 +363,7 @@ void InstructionSelector::VisitLoad(Node* node) {
     CHECK_NE(poisoning_level_, PoisoningMitigationLevel::kDontPoison);
     code |= MiscField::encode(kMemoryAccessPoisoned);
   }
-  Emit(code, 1, outputs, input_count, inputs, temp_count, temps);
+  Emit(code, 1, outputs, input_count, inputs);
 }
 
 void InstructionSelector::VisitPoisonedLoad(Node* node) { VisitLoad(node); }

src/x64/macro-assembler-x64.h

@@ -484,7 +484,7 @@ class V8_EXPORT_PRIVATE TurboAssembler : public TurboAssemblerBase {
   // When pointer compression is enabled, uses |scratch| to decompress the
   // value.
   void LoadAnyTaggedField(Register destination, Operand field_operand,
-                          Register scratch);
+                          Register scratch = kScratchRegister);
 
   // Loads a field containing a HeapObject, decompresses it if necessary and
   // pushes full pointer to the stack. When pointer compression is enabled,
@@ -509,7 +509,7 @@ class V8_EXPORT_PRIVATE TurboAssembler : public TurboAssemblerBase {
   void DecompressTaggedSigned(Register destination, Operand field_operand);
   void DecompressTaggedPointer(Register destination, Operand field_operand);
   void DecompressAnyTagged(Register destination, Operand field_operand,
-                           Register scratch);
+                           Register scratch = kScratchRegister);
 
  protected:
   static const int kSmiShift = kSmiTagSize + kSmiShiftSize;