PPC: Changes to allow AIX to compile with gcc 4.8.3

We were able to remove most of our changes needed to compile
on AIX with an earlier compiler level.  These changes are the
remaining ones.

The changes in heap/heap.cc are needed because otherwise the
compiler complains that result is potentially used before
it is initialized.

The changes in heap/mark-compact.cc are required because
AIX supports the full 64 bit address range so the check
being guarded is invalid.

The changes in build/toolchain.gypi and
test/cctest/cctest/gyp are aix only and are adjust the
compile/link options to allow the AIX build to succeed.

	modified:   build/toolchain.gypi
	modified:   src/heap/heap.cc
	modified:   src/heap/mark-compact.cc
	modified:   test/cctest/cctest.gyp

R=danno@chromium.org, svenpanne@chromium.org

BUG=

Review URL: https://codereview.chromium.org/1013833002

Cr-Commit-Position: refs/heads/master@{#27255}

build/toolchain.gypi

@@ -1144,6 +1144,11 @@
           }],
           ['OS=="aix"', {
             'ldflags': [ '-Wl,-bbigtoc' ],
+            'conditions': [
+              ['v8_target_arch=="ppc64"', {
+                'cflags': [ '-maix64 -mcmodel=large' ],
+              }],
+            ],
           }],
           ['OS=="android"', {
             'variables': {

src/heap/heap.cc

@@ -2899,7 +2899,7 @@ AllocationResult Heap::AllocatePropertyCell() {
 AllocationResult Heap::AllocateWeakCell(HeapObject* value) {
   int size = WeakCell::kSize;
   STATIC_ASSERT(WeakCell::kSize <= Page::kMaxRegularHeapObjectSize);
-  HeapObject* result;
+  HeapObject* result = NULL;
   {
     AllocationResult allocation =
         AllocateRaw(size, OLD_POINTER_SPACE, OLD_POINTER_SPACE);
@@ -4474,7 +4474,7 @@ AllocationResult Heap::AllocateExtendedConstantPoolArray(
 AllocationResult Heap::AllocateEmptyConstantPoolArray() {
   ConstantPoolArray::NumberOfEntries small(0, 0, 0, 0);
   int size = ConstantPoolArray::SizeFor(small);
-  HeapObject* result;
+  HeapObject* result = NULL;
   {
     AllocationResult allocation =
         AllocateRaw(size, OLD_DATA_SPACE, OLD_DATA_SPACE);
@@ -4490,7 +4490,7 @@ AllocationResult Heap::AllocateSymbol() {
   // Statically ensure that it is safe to allocate symbols in paged spaces.
   STATIC_ASSERT(Symbol::kSize <= Page::kMaxRegularHeapObjectSize);
 
-  HeapObject* result;
+  HeapObject* result = NULL;
   AllocationResult allocation =
       AllocateRaw(Symbol::kSize, OLD_POINTER_SPACE, OLD_POINTER_SPACE);
   if (!allocation.To(&result)) return allocation;

src/heap/mark-compact.cc

@@ -2877,11 +2877,13 @@ class PointersUpdatingVisitor : public ObjectVisitor {
 
 // TODO(ishell): remove, once crbug/454297 is caught.
 #if V8_TARGET_ARCH_64_BIT
+#ifndef V8_OS_AIX  // no point checking on AIX as full 64 range is supported
     const uintptr_t kBoundary = V8_UINT64_C(1) << 48;
     STATIC_ASSERT(kBoundary > 0);
     if (reinterpret_cast<uintptr_t>(heap_obj->address()) >= kBoundary) {
       CheckLayoutDescriptorAndDie(heap, slot);
     }
+#endif
 #endif
     MapWord map_word = heap_obj->map_word();
     if (map_word.IsForwardingAddress()) {

test/cctest/cctest.gyp

@@ -272,6 +272,9 @@
             },
           },
         }],
+        ['OS=="aix"', {
+          'ldflags': [ '-Wl,-bbigtoc' ],
+        }],
         ['component=="shared_library"', {
           # cctest can't be built against a shared library, so we need to
           # depend on the underlying static target in that case.