[csa] Remove double pointer load in Allocation with kDoubleAlignment.

AllocateRawAligned called into AllocateRawUnaligned, which expected
the address of the pointer to the top of the stack, not the pointer
itself. Instead, the pointer itself was passed, causing segfaults
if this code is actually run.

Also do some drive-by clean up of the branching/labels and unused
vars etc. in AllocateRawAligned.

BUG=v8:6075

Change-Id: If71db4b61d777b6543e5246e92bb5b9e6c02c81f
Reviewed-on: https://chromium-review.googlesource.com/452374Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43722}

src/code-stub-assembler.cc

@@ -747,33 +747,28 @@ Node* CodeStubAssembler::AllocateRawAligned(Node* size_in_bytes,
                                             Node* top_address,
                                             Node* limit_address) {
   Node* top = Load(MachineType::Pointer(), top_address);
-  Node* limit = Load(MachineType::Pointer(), limit_address);
   Variable adjusted_size(this, MachineType::PointerRepresentation(),
                          size_in_bytes);
   if (flags & kDoubleAlignment) {
-    Label aligned(this), not_aligned(this), merge(this, &adjusted_size);
+    Label not_aligned(this), done_alignment(this, &adjusted_size);
     Branch(WordAnd(top, IntPtrConstant(kDoubleAlignmentMask)), &not_aligned,
-           &aligned);
+           &done_alignment);
 
     Bind(&not_aligned);
     Node* not_aligned_size =
         IntPtrAdd(size_in_bytes, IntPtrConstant(kPointerSize));
     adjusted_size.Bind(not_aligned_size);
-    Goto(&merge);
-
-    Bind(&aligned);
-    Goto(&merge);
+    Goto(&done_alignment);
 
-    Bind(&merge);
+    Bind(&done_alignment);
   }
 
-  Variable address(
-      this, MachineRepresentation::kTagged,
-      AllocateRawUnaligned(adjusted_size.value(), kNone, top, limit));
+  Variable address(this, MachineRepresentation::kTagged,
+                   AllocateRawUnaligned(adjusted_size.value(), kNone,
+                                        top_address, limit_address));
 
-  Label needs_filler(this), doesnt_need_filler(this),
-      merge_address(this, &address);
-  Branch(IntPtrEqual(adjusted_size.value(), size_in_bytes), &doesnt_need_filler,
+  Label needs_filler(this), done_filling(this, &address);
+  Branch(IntPtrEqual(adjusted_size.value(), size_in_bytes), &done_filling,
          &needs_filler);
 
   Bind(&needs_filler);
@@ -782,12 +777,9 @@ Node* CodeStubAssembler::AllocateRawAligned(Node* size_in_bytes,
                       LoadRoot(Heap::kOnePointerFillerMapRootIndex));
   address.Bind(BitcastWordToTagged(
       IntPtrAdd(address.value(), IntPtrConstant(kPointerSize))));
-  Goto(&merge_address);
-
-  Bind(&doesnt_need_filler);
-  Goto(&merge_address);
+  Goto(&done_filling);
 
-  Bind(&merge_address);
+  Bind(&done_filling);
   // Update the top.
   StoreNoWriteBarrier(MachineType::PointerRepresentation(), top_address,
                       IntPtrAdd(top, adjusted_size.value()));