[PATCH] x86 NaCl: Emit LAHF/SAHF instead of PUSHF/POPF

[Tim Northover]

In my second attempt to make an intelligent comment here...

Doesn't this neglect the overflow flag?


================
Comment at: lib/Target/X86/X86InstrInfo.cpp:3281-3282
@@ +3280,4 @@
+      if (FromEFLAGS) {
+        BuildMI(MBB, MI, DL, get(X86::LAHF));
+        BuildMI(MBB, MI, DL, get(Mov), Reg).addReg(AX);
+      }
----------------
jfb wrote:
> t.p.northover wrote:
> > I don't think this works. This expansion occurs post-RA doesn't it? In which case AX could be live.
> Correct, that's why AX is pushed/popped before and after lahf/sahf.
Oh bother, don't know how I missed that. Sorry.

http://reviews.llvm.org/D6629

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