[Turbofan] Add the concept of aliasing to RegisterConfiguration.

src/compiler/arm/code-generator-arm.cc

Index: src/compiler/arm/code-generator-arm.cc
diff --git a/src/compiler/arm/code-generator-arm.cc b/src/compiler/arm/code-generator-arm.cc
index 88f3d79360ccbb73c4c16cf0535387b3ac4782cd..627258036fa8867104f8bdaef5877217a25afceb 100644
--- a/src/compiler/arm/code-generator-arm.cc
+++ b/src/compiler/arm/code-generator-arm.cc
@@ -36,7 +36,9 @@ class ArmOperandConverter final : public InstructionOperandConverter {
   }
 
   SwVfpRegister ToFloat32Register(InstructionOperand* op) {

[Mircea Trofin, 2016/06/22 06:07:34]

If this is only called for LocationOperands, should we change the signature
accordingly?

[bbudge, 2016/06/22 20:16:03]

I followed the pattern of ToFloat64Register. Changing the signature would
require casts at all the call sites (there are about 10 for both functions).

-    return ToFloat64Register(op).low();
+    DCHECK(LocationOperand::cast(op)->representation() ==
+           MachineRepresentation::kFloat32);
+    return LocationOperand::cast(op)->GetFloatRegister();
   }
 
   LowDwVfpRegister OutputFloat64Register(size_t index = 0) {