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

src/x64/assembler-x64.cc

 // Copyright 2009 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 102 matching lines @@
   __ jmp(&done);
 
   // Invoke CPUID with 1 in eax to get feature information in
   // ecx:edx. Temporarily enable CPUID support because we know it's
   // safe here.
   __ bind(&cpuid);
   __ movq(rax, Immediate(1));
   supported_ = kDefaultCpuFeatures | (1 << CPUID);
   { Scope fscope(CPUID);
     __ cpuid();
+    // Move the result from ecx:edx to rdi.
+    __ movl(rdi, rdx);  // Zero-extended to 64 bits.
+    __ shl(rcx, Immediate(32));
+    __ or_(rdi, rcx);
+
+    // Get the sahf supported flag, from CPUID(0x80000001)
+    __ movq(rax, 0x80000001, RelocInfo::NONE);
+    __ cpuid();
   }
   supported_ = kDefaultCpuFeatures;
 
-  // Move the result from ecx:edx to rax and make sure to mark the
-  // CPUID feature as supported.
-  __ movl(rax, rdx);  // Zero-extended to 64 bits.
-  __ shl(rcx, Immediate(32));
+  // Put the CPU flags in rax.
+  // rax = (rcx & 1) | (rdi & ~1) | (1 << CPUID).
+  __ movl(rax, Immediate(1));
+  __ and_(rcx, rax);  // Bit 0 is set if SAHF instruction supported.
+  __ not_(rax);
+  __ and_(rax, rdi);
   __ or_(rax, rcx);
   __ or_(rax, Immediate(1 << CPUID));
 
   // Done.
   __ bind(&done);
   __ movq(rsp, rbp);
   __ pop(rbx);
   __ pop(rcx);
   __ popfq();
   __ pop(rbp);
@@ skipping 2208 matching lines @@
     RecordRelocInfo(RelocInfo::POSITION, current_position_);
     written_position_ = current_position_;
   }
 }
 
 
 const int RelocInfo::kApplyMask = 1 << RelocInfo::INTERNAL_REFERENCE;
 
 
 } }  // namespace v8::internal