Improve register allocation for Lithium representation changes on ARM...

src/arm/lithium-arm.cc

Index: src/arm/lithium-arm.cc
===================================================================
--- src/arm/lithium-arm.cc	(revision 10400)
+++ src/arm/lithium-arm.cc	(working copy)
@@ -1625,12 +1625,14 @@
       return AssignEnvironment(DefineAsRegister(res));
     } else {
       ASSERT(to.IsInteger32());
-      LOperand* value = UseRegister(instr->value());
+      LOperand* value;

[fschneider, 2012/01/16 12:59:20]

You can write:

LOperand* value = UseRegisterAtStart(instr->value());

here and the code below will be simpler.

[Alexandre, 2012/01/16 13:07:18]

Done.

       bool needs_check = !instr->value()->type().IsSmi();
       LInstruction* res = NULL;
       if (!needs_check) {
-        res = DefineSameAsFirst(new LSmiUntag(value, needs_check));
+        value = UseRegisterAtStart(instr->value());
+        res = DefineAsRegister(new LSmiUntag(value, needs_check));
       } else {
+        value = UseRegister(instr->value());

[fschneider, 2012/01/16 12:59:20]

In this case you can also use UseRegisterAtStart. When defining the result with
DefineSameAsFirst, UseRegister and UseRegisterAtStart are equivalent for the
first input.

[Alexandre, 2012/01/16 13:07:18]

Done.

         LOperand* temp1 = TempRegister();
         LOperand* temp2 = instr->CanTruncateToInt32() ? TempRegister()
                                                       : NULL;
@@ -1665,12 +1667,12 @@
   } else if (from.IsInteger32()) {
     if (to.IsTagged()) {
       HValue* val = instr->value();
-      LOperand* value = UseRegister(val);
+      LOperand* value = UseRegisterAtStart(val);
       if (val->HasRange() && val->range()->IsInSmiRange()) {
-        return DefineSameAsFirst(new LSmiTag(value));
+        return DefineAsRegister(new LSmiTag(value));
       } else {
         LNumberTagI* result = new LNumberTagI(value);
-        return AssignEnvironment(AssignPointerMap(DefineSameAsFirst(result)));
+        return AssignEnvironment(AssignPointerMap(DefineAsRegister(result)));
       }
     } else {
       ASSERT(to.IsDouble());