[PATCH] D36414: [X86][X87] Ensure x87 instructions are tagged as altering the FPSW reg

David Kreitzer via Phabricator via llvm-commits llvm-commits at lists.llvm.org
Thu Aug 10 07:57:20 PDT 2017

DavidKreitzer added a comment.

The change looks correct to me modulo Craig's comment, though I suspect he's right that there is a bug in the Intel documentation for FNOP.

Regarding testing, would it be possible to write MI tests that run through the MIScheduler in misched-bottomup mode? The idea would be to construct an MI sequence similar to this:

  fxam ; or some other FPSW-defining instruction you want to test
  fstsw ax

I am not intimately familiar with the instruction scheduler, but if misched-bottomup behaves as its name implies, I would expect the fxam to be incorrectly hoisted above the fcom without your fix.



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