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

src/a64/lithium-codegen-a64.cc

Index: src/a64/lithium-codegen-a64.cc
diff --git a/src/a64/lithium-codegen-a64.cc b/src/a64/lithium-codegen-a64.cc
index da03ccc214700a949048b590d342a434f84521c2..0e2f40c3c4291b41d9fd69b9afadcdd617e0e191 100644
--- a/src/a64/lithium-codegen-a64.cc
+++ b/src/a64/lithium-codegen-a64.cc
@@ -5493,7 +5493,7 @@ void LCodeGen::DoTruncateDoubleToIntOrSmi(LTruncateDoubleToIntOrSmi* instr) {
                     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.

 }