Fixes obo error in javascript int checking.

runtime/vm/intermediate_language_x64.cc

Index: runtime/vm/intermediate_language_x64.cc
===================================================================
--- runtime/vm/intermediate_language_x64.cc	(revision 25732)
+++ runtime/vm/intermediate_language_x64.cc	(working copy)
@@ -2151,20 +2151,15 @@
 }
 
 
-static void Emit54BitOverflowCheck(FlowGraphCompiler* compiler,
-                                   Label* overflow,
-                                   Register result) {
+static void EmitJavascriptOverflowCheck(FlowGraphCompiler* compiler,
+                                        Label* overflow,
+                                        Register result) {
   if (FLAG_throw_on_javascript_int_overflow) {
     ASSERT(overflow != NULL);
-    __ movq(TMP, result);  // result is a tagged Smi.
-    // Bits 55...64 must be all 0 or all 1. (It would be bit 54, but result
-    // is tagged.)
-    __ shlq(result, Immediate(64 - 55));
-    __ sarq(result, Immediate(64 - 55));
-    __ cmpq(result, TMP);
-    __ j(NOT_EQUAL, overflow);  // 54-bit overflow.
-    __ cmpq(result, Immediate(-0x1FFFFFFFFFFFFFLL - 1));
-    __ j(EQUAL, overflow);  // The most negative 54-bit int is also disallowed.
+    __ cmpq(result, Immediate(-0x20000000000000));
+    __ j(LESS, overflow);
+    __ cmpq(result, Immediate(0x20000000000000));
+    __ j(GREATER, overflow);
   }
 }
 
@@ -2208,7 +2203,7 @@
       // Shift for result now we know there is no overflow.
       __ shlq(left, Immediate(value));
     }
-    Emit54BitOverflowCheck(compiler, deopt, result);
+    EmitJavascriptOverflowCheck(compiler, deopt, result);
     return;
   }
 
@@ -2238,7 +2233,7 @@
       __ SmiUntag(right);
       __ shlq(left, right);
     }
-    Emit54BitOverflowCheck(compiler, deopt, result);
+    EmitJavascriptOverflowCheck(compiler, deopt, result);
     return;
   }
 
@@ -2289,7 +2284,7 @@
     // Shift for result now we know there is no overflow.
     __ shlq(left, right);
   }
-  Emit54BitOverflowCheck(compiler, deopt, result);
+  EmitJavascriptOverflowCheck(compiler, deopt, result);
 }
 
 
@@ -2488,7 +2483,7 @@
         UNREACHABLE();
         break;
     }
-    Emit54BitOverflowCheck(compiler, deopt, result);
+    EmitJavascriptOverflowCheck(compiler, deopt, result);
     return;
   }  // locs()->in(1).IsConstant().
 
@@ -2531,7 +2526,7 @@
         UNREACHABLE();
         break;
     }
-    Emit54BitOverflowCheck(compiler, deopt, result);
+    EmitJavascriptOverflowCheck(compiler, deopt, result);
     return;
   }  // locs()->in(1).IsStackSlot().
 
@@ -2661,7 +2656,7 @@
       UNREACHABLE();
       break;
   }
-  Emit54BitOverflowCheck(compiler, deopt, result);
+  EmitJavascriptOverflowCheck(compiler, deopt, result);
 }
 
 
@@ -3839,7 +3834,7 @@
                                             kDeoptUnaryOp);
       __ negq(value);
       __ j(OVERFLOW, deopt);
-      Emit54BitOverflowCheck(compiler, deopt, value);
+      EmitJavascriptOverflowCheck(compiler, deopt, value);
       break;
     }
     case Token::kBIT_NOT:
@@ -3900,7 +3895,7 @@
   __ shlq(temp, Immediate(1));
   __ j(OVERFLOW, &do_call, Assembler::kNearJump);
   __ SmiTag(result);
-  Emit54BitOverflowCheck(compiler, &do_call, result);
+  EmitJavascriptOverflowCheck(compiler, &do_call, result);
   __ jmp(&done);
   __ Bind(&do_call);
   ASSERT(instance_call()->HasICData());
@@ -3946,7 +3941,7 @@
   __ shlq(temp, Immediate(1));
   __ j(OVERFLOW, deopt);
   __ SmiTag(result);
-  Emit54BitOverflowCheck(compiler, deopt, result);
+  EmitJavascriptOverflowCheck(compiler, deopt, result);
 }