Specialize mint shift code on ia32 for a constant shift amount.

runtime/vm/assembler_ia32_test.cc

Index: runtime/vm/assembler_ia32_test.cc
===================================================================
--- runtime/vm/assembler_ia32_test.cc	(revision 38138)
+++ runtime/vm/assembler_ia32_test.cc	(working copy)
@@ -553,7 +553,28 @@
   __ Bind(&donetest15);
   __ addl(ESP, Immediate(kWordSize));
 
+  Label donetest16;
+  __ movl(EDX, Immediate(0x80000000));
   __ movl(EAX, Immediate(0));
+  __ movl(ECX, Immediate(3));
+  __ sarl(EDX, Immediate(3));
+  __ shrd(EDX, EAX, Immediate(3));
+  __ cmpl(EDX, Immediate(0x1e000000));
+  __ j(EQUAL, &donetest16);
+  __ int3();
+  __ Bind(&donetest16);
+
+  Label donetest17;
+  __ movl(EDX, Immediate(0xFF000000));
+  __ movl(EAX, Immediate(-1));
+  __ shll(EDX, Immediate(2));
+  __ shld(EDX, EAX, Immediate(2));
+  __ cmpl(EDX, Immediate(0xF0000003));
+  __ j(EQUAL, &donetest17);
+  __ int3();
+  __ Bind(&donetest17);
+
+  __ movl(EAX, Immediate(0));
   __ ret();
 }