PPC: [compiler] Drop the CompareNilIC.

Port fb59ea33

Original commit message:
    Since both null and undefined are also marked as undetectable now, we
    can just test that bit instead of having the CompareNilIC try to collect
    feedback to speed up the general case (without the undetectable bit
    being used).

    Drive-by-fix: Update the type system to match the new handling of
    undetectable in the runtime.

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

Review URL: https://codereview.chromium.org/1742333002

Cr-Commit-Position: refs/heads/master@{#34371}

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

@@ -3994,10 +3994,11 @@ void FullCodeGenerator::EmitLiteralCompareNil(CompareOperation* expr,
     __ cmp(r3, r4);
     Split(eq, if_true, if_false, fall_through);
   } else {
-    Handle<Code> ic = CompareNilICStub::GetUninitialized(isolate(), nil);
-    CallIC(ic, expr->CompareOperationFeedbackId());
-    __ CompareRoot(r3, Heap::kTrueValueRootIndex);
-    Split(eq, if_true, if_false, fall_through);
+    __ JumpIfSmi(r3, if_false);
+    __ LoadP(r3, FieldMemOperand(r3, HeapObject::kMapOffset));
+    __ lbz(r4, FieldMemOperand(r3, Map::kBitFieldOffset));
+    __ andi(r0, r4, Operand(1 << Map::kIsUndetectable));
+    Split(ne, if_true, if_false, fall_through, cr0);
   }
   context()->Plug(if_true, if_false);
 }

src/ppc/interface-descriptors-ppc.cc

@@ -314,13 +314,6 @@ void CompareDescriptor::InitializePlatformSpecific(
 }
 
 
-void CompareNilDescriptor::InitializePlatformSpecific(
-    CallInterfaceDescriptorData* data) {
-  Register registers[] = {r3};
-  data->InitializePlatformSpecific(arraysize(registers), registers);
-}
-
-
 void ToBooleanDescriptor::InitializePlatformSpecific(
     CallInterfaceDescriptorData* data) {
   Register registers[] = {r3};