PPC: [fullcode] Switch passing of new.target to register.

Port 440a42b7

Original commit message:
    This passes the new.target value in a register instead of through a
    side-channel via the construct stub. Note that this marks the last
    consumer of said side-channel and the special slot in the construct
    stub frame can be removed as a follow-up.

R=mstarzinger@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com
TEST=mjsunit/es6/regress/regress-new-target-context
BUG=

Review URL: https://codereview.chromium.org/1494003004

Cr-Commit-Position: refs/heads/master@{#32585}

src/full-codegen/ppc/full-codegen-ppc.cc

@@ -89,6 +89,7 @@ class JumpPatchSite BASE_EMBEDDED {
 //
 // The live registers are:
 //   o r4: the JS function object being called (i.e., ourselves)
+//   o r6: the new target value
 //   o cp: our context
 //   o fp: our caller's frame pointer (aka r31)
 //   o sp: stack pointer
@@ -187,14 +188,24 @@ void FullCodeGenerator::Generate() {
       __ Push(info->scope()->GetScopeInfo(info->isolate()));
       __ CallRuntime(Runtime::kNewScriptContext, 2);
       PrepareForBailoutForId(BailoutId::ScriptContext(), TOS_REG);
-    } else if (slots <= FastNewContextStub::kMaximumSlots) {
-      FastNewContextStub stub(isolate(), slots);
-      __ CallStub(&stub);
-      // Result of FastNewContextStub is always in new space.
-      need_write_barrier = false;
+      // The new target value is not used, clobbering is safe.
+      DCHECK_NULL(info->scope()->new_target_var());
     } else {
-      __ push(r4);
-      __ CallRuntime(Runtime::kNewFunctionContext, 1);
+      if (info->scope()->new_target_var() != nullptr) {
+        __ push(r6);  // Preserve new target.
+      }
+      if (slots <= FastNewContextStub::kMaximumSlots) {
+        FastNewContextStub stub(isolate(), slots);
+        __ CallStub(&stub);
+        // Result of FastNewContextStub is always in new space.
+        need_write_barrier = false;
+      } else {
+        __ push(r4);
+        __ CallRuntime(Runtime::kNewFunctionContext, 1);
+      }
+      if (info->scope()->new_target_var() != nullptr) {
+        __ pop(r6);  // Preserve new target.
+      }
     }
     function_in_register_r4 = false;
     // Context is returned in r3.  It replaces the context passed to us.
@@ -217,7 +228,7 @@ void FullCodeGenerator::Generate() {
 
         // Update the write barrier.
         if (need_write_barrier) {
-          __ RecordWriteContextSlot(cp, target.offset(), r3, r6,
+          __ RecordWriteContextSlot(cp, target.offset(), r3, r5,
                                     kLRHasBeenSaved, kDontSaveFPRegs);
         } else if (FLAG_debug_code) {
           Label done;
@@ -228,11 +239,11 @@ void FullCodeGenerator::Generate() {
       }
     }
   }
-  PrepareForBailoutForId(BailoutId::FunctionContext(), NO_REGISTERS);
 
-  // Function register is trashed in case we bailout here. But since that
-  // could happen only when we allocate a context the value of
-  // |function_in_register_r4| is correct.
+  // Register holding this function and new target are both trashed in case we
+  // bailout here. But since that can happen only when new target is not used
+  // and we allocate a context, the value of |function_in_register| is correct.
+  PrepareForBailoutForId(BailoutId::FunctionContext(), NO_REGISTERS);
 
   // Possibly set up a local binding to the this function which is used in
   // derived constructors with super calls.
@@ -246,36 +257,11 @@ void FullCodeGenerator::Generate() {
     SetVar(this_function_var, r4, r3, r5);
   }
 
+  // Possibly set up a local binding to the new target value.
   Variable* new_target_var = scope()->new_target_var();
   if (new_target_var != nullptr) {
     Comment cmnt(masm_, "[ new.target");
-
-    // Get the frame pointer for the calling frame.
-    __ LoadP(r5, MemOperand(fp, StandardFrameConstants::kCallerFPOffset));
-
-    // Skip the arguments adaptor frame if it exists.
-    __ LoadP(r4, MemOperand(r5, StandardFrameConstants::kContextOffset));
-    __ CmpSmiLiteral(r4, Smi::FromInt(StackFrame::ARGUMENTS_ADAPTOR), r0);
-    Label skip;
-    __ bne(&skip);
-    __ LoadP(r5, MemOperand(r5, StandardFrameConstants::kCallerFPOffset));
-    __ bind(&skip);
-
-    // Check the marker in the calling frame.
-    __ LoadP(r4, MemOperand(r5, StandardFrameConstants::kMarkerOffset));
-    __ CmpSmiLiteral(r4, Smi::FromInt(StackFrame::CONSTRUCT), r0);
-    Label non_construct_frame, done;
-    function_in_register_r4 = false;
-
-    __ bne(&non_construct_frame);
-    __ LoadP(r3, MemOperand(r5, ConstructFrameConstants::kNewTargetOffset));
-    __ b(&done);
-
-    __ bind(&non_construct_frame);
-    __ LoadRoot(r3, Heap::kUndefinedValueRootIndex);
-    __ bind(&done);
-
-    SetVar(new_target_var, r3, r5, r6);
+    SetVar(new_target_var, r6, r3, r5);
   }
 
   Variable* arguments = scope()->arguments();