PPC: [generators] Implement Generator.prototype.return.

Port dbd86408

Original commit message:
    Note: This is currently only used by yield*, we still need to support it in
    other places (such as for-of loops).  It can be used manually of course.

    (This CL does not touch the full-codegen implementation of yield* because that
    code is already dead.  The yield* desugaring already supports return and doesn't
    need to be touched.)

R=neis@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=v8:3566
LOG=y

Review URL: https://codereview.chromium.org/1664413002

Cr-Commit-Position: refs/heads/master@{#33754}

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

@@ -1895,8 +1895,17 @@ void FullCodeGenerator::VisitYield(Yield* expr) {
 
       __ b(&suspend);
       __ bind(&continuation);
+      // When we arrive here, the stack top is the resume mode and
+      // result_register() holds the input value (the argument given to the
+      // respective resume operation).
       __ RecordGeneratorContinuation();
-      __ b(&resume);
+      __ pop(r4);
+      __ CmpSmiLiteral(r4, Smi::FromInt(JSGeneratorObject::RETURN), r0);
+      __ bne(&resume);
+      __ push(result_register());
+      EmitCreateIteratorResult(true);
+      EmitUnwindBeforeReturn();
+      EmitReturnSequence();
 
       __ bind(&suspend);
       VisitForAccumulatorValue(expr->generator_object());
@@ -2124,6 +2133,7 @@ void FullCodeGenerator::EmitGeneratorResume(
                         Smi::FromInt(JSGeneratorObject::kGeneratorExecuting));
       __ StoreP(r5, FieldMemOperand(r4, JSGeneratorObject::kContinuationOffset),
                 r0);
+      __ Push(Smi::FromInt(resume_mode));  // Consumed in continuation.
       __ Jump(ip);
       __ bind(&slow_resume);
     }
@@ -2140,6 +2150,7 @@ void FullCodeGenerator::EmitGeneratorResume(
   __ bdnz(&operand_loop);
 
   __ bind(&call_resume);
+  __ Push(Smi::FromInt(resume_mode));  // Consumed in continuation.
   DCHECK(!result_register().is(r4));
   __ Push(r4, result_register());
   __ Push(Smi::FromInt(resume_mode));