Revert change to Smi check that was a performance regression.

src/codegen-ia32.cc

Index: src/codegen-ia32.cc
===================================================================
--- src/codegen-ia32.cc	(revision 1142)
+++ src/codegen-ia32.cc	(working copy)
@@ -1127,14 +1127,14 @@
         __ j(not_zero, deferred->enter(), not_taken);
         __ sar(ebx, kSmiTagSize);
         __ shl(ebx, shift_value);
-        // Convert the int to a Smi, and check that it is in
-        // the range of valid Smis.
-        ASSERT(kSmiTagSize == times_2);  // Adjust code if not true.
-        ASSERT(kSmiTag == 0);  // Adjust code if not true.
-        __ add(ebx, Operand(ebx));
-        __ j(overflow, deferred->enter(), not_taken);
-        __ mov(eax, Operand(ebx));
-
+        // This is the Smi check for the shifted result.
+        // After signed subtraction of 0xc0000000, the valid 
+        // Smis are positive.
+        __ cmp(ebx, 0xc0000000);
+        __ j(sign, deferred->enter(), not_taken); 
+        // tag result and store it in TOS (eax)
+        ASSERT(kSmiTagSize == times_2);  // adjust code if not the case
+        __ lea(eax, Operand(ebx, ebx, times_1, kSmiTag));
         __ bind(deferred->exit());
         frame_->Push(eax);
       }