[ia32] Fixes a bug in cmpw.

test/cctest/test-assembler-ia32.cc

Index: test/cctest/test-assembler-ia32.cc
diff --git a/test/cctest/test-assembler-ia32.cc b/test/cctest/test-assembler-ia32.cc
index 12733c2cdda3ddf7296f71739c2334ed83df351a..f6df9ecf294e087c6523df06c20ce36101265f6a 100644
--- a/test/cctest/test-assembler-ia32.cc
+++ b/test/cctest/test-assembler-ia32.cc
@@ -1497,4 +1497,45 @@ TEST(AssemblerIa32JumpTables2) {
   }
 }
 
+TEST(Regress621926) {
+  // Bug description:
+  // The opcodes for cmpw r/m16, r16 and cmpw r16, r/m16 were swapped.
+  // This was causing non-commutative comparisons to produce the wrong result.
+  CcTest::InitializeVM();
+  Isolate* isolate = reinterpret_cast<Isolate*>(CcTest::isolate());
+  HandleScope scope(isolate);
+  Assembler assm(isolate, nullptr, 0);
+
+  int16_t a = 42;
+
+  Label fail;
+  __ push(ebx);
+  __ mov(ebx, Immediate(reinterpret_cast<intptr_t>(&a)));
+  __ mov(eax, Immediate(41));
+  __ cmpw(eax, Operand(ebx));
+  __ j(above_equal, &fail);
+  __ cmpw(Operand(ebx), eax);
+  __ j(below_equal, &fail);
+  __ mov(eax, 1);
+  __ pop(ebx);
+  __ ret(0);
+  __ bind(&fail);
+  __ mov(eax, 0);
+  __ pop(ebx);
+  __ ret(0);
+
+  CodeDesc desc;
+  assm.GetCode(&desc);
+  Handle<Code> code = isolate->factory()->NewCode(
+      desc, Code::ComputeFlags(Code::STUB), Handle<Code>());
+
+#ifdef OBJECT_PRINT
+  OFStream os(stdout);
+  code->Print(os);
+#endif
+
+  F0 f = FUNCTION_CAST<F0>(code->entry());
+  CHECK_EQ(f(), 1);
+}
+
 #undef __