X64: Use sahf instruction only on processors that support it.

src/x64/codegen-x64.cc

Index: src/x64/codegen-x64.cc
===================================================================
--- src/x64/codegen-x64.cc	(revision 2791)
+++ src/x64/codegen-x64.cc	(working copy)
@@ -7722,18 +7722,29 @@
         __ fild_s(Operand(rsp, 0 * kPointerSize));
         __ fucompp();
         __ fnstsw_ax();
-        __ sahf();  // TODO(X64): Not available.
-        __ j(not_zero, &operand_conversion_failure);
-        __ j(parity_even, &operand_conversion_failure);
-
+        if (CpuFeatures::IsSupported(CpuFeatures::SAHF)) {
+          __ sahf();
+          __ j(not_zero, &operand_conversion_failure);
+          __ j(parity_even, &operand_conversion_failure);
+        } else {
+          __ and_(rax, Immediate(0x4400));
+          __ cmpl(rax, Immediate(0x4000));
+          __ j(not_zero, &operand_conversion_failure);
+        }
         // Check if left operand is int32.
         __ fist_s(Operand(rsp, 1 * kPointerSize));
         __ fild_s(Operand(rsp, 1 * kPointerSize));
         __ fucompp();
         __ fnstsw_ax();
-        __ sahf();  // TODO(X64): Not available. Test bits in ax directly
-        __ j(not_zero, &operand_conversion_failure);
-        __ j(parity_even, &operand_conversion_failure);
+        if (CpuFeatures::IsSupported(CpuFeatures::SAHF)) {
+          __ sahf();
+          __ j(not_zero, &operand_conversion_failure);
+          __ j(parity_even, &operand_conversion_failure);
+        } else {
+          __ and_(rax, Immediate(0x4400));
+          __ cmpl(rax, Immediate(0x4000));
+          __ j(not_zero, &operand_conversion_failure);
+        }
       }
 
       // Get int32 operands and perform bitop.