A64: When truncating to an int, store the result in a 64bit register

src/a64/lithium-codegen-a64.cc

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@@ skipping 5475 matching lines @@
 
 
 void LCodeGen::DoTruncateDoubleToIntOrSmi(LTruncateDoubleToIntOrSmi* instr) {
   DoubleRegister input = ToDoubleRegister(instr->value());
   Register result = ToRegister(instr->result());
   __ ECMA262ToInt32(result, input,
                     ToRegister(instr->temp1()),
                     ToRegister(instr->temp2()),
                     instr->tag_result()
                         ? MacroAssembler::SMI
-                        : MacroAssembler::INT32_IN_W);
+                        : MacroAssembler::INT32);

[jbramley, 2014/02/11 12:58:50]

Our convention for Lithium instructions is to leave the top word of an int32
value undefined. This allows some minor efficiency improvements. We make similar
assumptions elsewhere too.

Have you found a case where the top 32 bits are read? If an A64 Lithium
instruction takes an Integer32 representation, it shouldn't read the top word.

 }
 
 
 void LCodeGen::DoTypeof(LTypeof* instr) {
   Register input = ToRegister(instr->value());
   __ Push(input);
   CallRuntime(Runtime::kTypeof, 1, instr);
 }
 
 
@@ skipping 187 matching lines @@
   __ Bind(&out_of_object);
   __ Ldr(result, FieldMemOperand(object, JSObject::kPropertiesOffset));
   // Index is equal to negated out of object property index plus 1.
   __ Sub(result, result, Operand::UntagSmiAndScale(index, kPointerSizeLog2));
   __ Ldr(result, FieldMemOperand(result,
                                  FixedArray::kHeaderSize - kPointerSize));
   __ Bind(&done);
 }
 
 } }  // namespace v8::internal