8341178: TypeRawPtr::add_offset may be "miscompiled" due to UB

Reviewed-by: dlong, kvn

Author: Kim Barrett

src/hotspot/share/opto/type.cpp

@@ -3111,8 +3111,8 @@ const TypeRawPtr *TypeRawPtr::make( enum PTR ptr ) {
   return (TypeRawPtr*)(new TypeRawPtr(ptr,nullptr))->hashcons();
 }
 
-const TypeRawPtr *TypeRawPtr::make( address bits ) {
-  assert( bits, "Use TypePtr for null" );
+const TypeRawPtr *TypeRawPtr::make(address bits) {
+  assert(bits != nullptr, "Use TypePtr for null");
   return (TypeRawPtr*)(new TypeRawPtr(Constant,bits))->hashcons();
 }
 
@@ -3201,15 +3201,21 @@ const TypePtr* TypeRawPtr::add_offset(intptr_t offset) const {
   case TypePtr::BotPTR:
   case TypePtr::NotNull:
     return this;
-  case TypePtr::Null:
   case TypePtr::Constant: {
-    address bits = _bits+offset;
-    if ( bits == 0 ) return TypePtr::NULL_PTR;
-    return make( bits );
+    uintptr_t bits = (uintptr_t)_bits;
+    uintptr_t sum = bits + offset;
+    if (( offset < 0 )
+        ? ( sum > bits )        // Underflow?
+        : ( sum < bits )) {     // Overflow?
+      return BOTTOM;
+    } else if ( sum == 0 ) {
+      return TypePtr::NULL_PTR;
+    } else {
+      return make( (address)sum );
+    }
   }
   default:  ShouldNotReachHere();
   }
-  return nullptr;                  // Lint noise
 }
 
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