PPC: [turbofan] Load immortal heap objects from the heap roots.

Port 5d2de78a

Original commit message:
It's cheaper to materialize heap constants by loading from the roots
array instead of embedding the constant into the instruction stream, at
least on x64, arm and arm64.

Drive-by-fix: Also cleanup the materialize constant from frame
optimization.

R=michael_dawson@ca.ibm.com
BUG=

Review URL: https://codereview.chromium.org/1075303003

Cr-Commit-Position: refs/heads/master@{#27823}

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

@@ -1350,18 +1350,12 @@ void CodeGenerator::AssembleMove(InstructionOperand* source,
           break;
         case Constant::kHeapObject: {
           Handle<HeapObject> src_object = src.ToHeapObject();
-          if (info()->IsOptimizing() &&
-              src_object.is_identical_to(info()->context())) {
-            // Loading the context from the frame is way cheaper than
-            // materializing the actual context heap object address.
-            __ LoadP(dst,
-                     MemOperand(fp, StandardFrameConstants::kContextOffset));
-          } else if (info()->IsOptimizing() &&
-                     src_object.is_identical_to(info()->closure())) {
-            // Loading the JSFunction from the frame is way cheaper than
-            // materializing the actual JSFunction heap object address.
-            __ LoadP(dst,
-                     MemOperand(fp, JavaScriptFrameConstants::kFunctionOffset));
+          Heap::RootListIndex index;
+          int offset;
+          if (IsMaterializableFromFrame(src_object, &offset)) {
+            __ LoadP(dst, MemOperand(fp, offset));
+          } else if (IsMaterializableFromRoot(src_object, &index)) {
+            __ LoadRoot(dst, index);
           } else {
             __ Move(dst, src_object);
           }