Refactor OSR related code to prepare for "true" OSR.

- Make the compiler restore all callee-save registers.
- Make the compiler return any value in a core register: this simplifies
  the current stub, and will also avoid having to look at the return
  type (and reading the shorty) when returning to an nterp frame.
- Add OsrData and offsets of its members to be used by nterp.

Test: test.py
Bug: 27094810
Change-Id: Ifa4f4877ab8b1f0c6a96feccea30c909942eb2fa
diff --git a/compiler/optimizing/code_generator_arm64.cc b/compiler/optimizing/code_generator_arm64.cc
index d3ce2db..64ec987 100644
--- a/compiler/optimizing/code_generator_arm64.cc
+++ b/compiler/optimizing/code_generator_arm64.cc
@@ -5530,7 +5530,21 @@
   locations->SetInAt(0, ARM64ReturnLocation(return_type));
 }
 
-void InstructionCodeGeneratorARM64::VisitReturn(HReturn* instruction ATTRIBUTE_UNUSED) {
+void InstructionCodeGeneratorARM64::VisitReturn(HReturn* ret) {
+  if (GetGraph()->IsCompilingOsr()) {
+    // To simplify callers of an OSR method, we put the return value in both
+    // floating point and core register.
+    switch (ret->InputAt(0)->GetType()) {
+      case DataType::Type::kFloat32:
+        __ Fmov(w0, s0);
+        break;
+      case DataType::Type::kFloat64:
+        __ Fmov(x0, d0);
+        break;
+      default:
+        break;
+    }
+  }
   codegen_->GenerateFrameExit();
 }