[turbofan] Allow for 32-bit field offsets in store elimination.

R=jarin
BUG=chromium:637121

Review-Url: https://codereview.chromium.org/2252283004
Cr-Commit-Position: refs/heads/master@{#38899}

src/compiler/store-store-elimination.cc

@@ -72,9 +72,7 @@ namespace compiler {
 
 namespace {
 
-// 16 bits was chosen fairly arbitrarily; it seems enough now. 8 bits is too
-// few.
-typedef uint16_t StoreOffset;
+typedef uint32_t StoreOffset;
 
 struct UnobservableStore {
   NodeId id_;
@@ -171,11 +169,11 @@ class RedundantStoreFinder final {
   const UnobservablesSet unobservables_visited_empty_;
 };
 
-// To safely cast an offset from a FieldAccess, which has a wider range
-// (namely int).
+// To safely cast an offset from a FieldAccess, which has a potentially wider
+// range (namely int).
 StoreOffset ToOffset(int offset) {
-  CHECK(0 <= offset && offset < (1 << 8 * sizeof(StoreOffset)));
-  return (StoreOffset)offset;
+  CHECK(0 <= offset);
+  return static_cast<StoreOffset>(offset);
 }
 
 StoreOffset ToOffset(const FieldAccess& access) {