[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 1d6c440409f7c9ba5c4a8d0ca221c904ed7916a3..45908103f4d79c26dae96ceb8673d347569bfe52 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) {
-    return ToFloat64Register(op).low();
+    DCHECK(LocationOperand::cast(op)->representation() ==
+           MachineRepresentation::kFloat32);
+    return LocationOperand::cast(op)->GetFloatRegister();
   }
 
   LowDwVfpRegister OutputFloat64Register(size_t index = 0) {