PPC: [turbofan] Add an operator to access the parent frame pointer

Port fd8fd05c

Original commit message:
    This functionality is useful for stubs that need to walk the stack. The new
    machine operator, LoadParentFramePointer dosn't force the currently compiling
    method to have a frame in contrast to LoadFramePointer. Instead, it adapts
    accordingly when frame elision is possible, making efficient stack walks
    possible without incurring a performance penalty for small stubs that can
    benefit from frame elision.

R=danno@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=

Review URL: https://codereview.chromium.org/1700323002

Cr-Commit-Position: refs/heads/master@{#34049}

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

@@ -821,6 +821,13 @@ void CodeGenerator::AssembleArchInstruction(Instruction* instr) {
       __ mr(i.OutputRegister(), fp);
       DCHECK_EQ(LeaveRC, i.OutputRCBit());
       break;
+    case kArchParentFramePointer:
+      if (frame_access_state()->frame()->needs_frame()) {
+        __ LoadP(i.OutputRegister(), MemOperand(fp, 0));
+      } else {
+        __ mr(i.OutputRegister(), fp);
+      }
+      break;
     case kArchTruncateDoubleToI:
       // TODO(mbrandy): move slow call to stub out of line.
       __ TruncateDoubleToI(i.OutputRegister(), i.InputDoubleRegister(0));