[Qemu-devel] [RFC] TCG new op: setcond

[Laurent Desnogues]

Hello,

this patch implements a new TCG op, setcond, that sets a temp
to 1 if the condition is true, else to 0.  The benefit is the potential
removal of brcond instructions, and helpers size reduction which
can lead to using TCG instead of helpers.

This patch is only posted here to get comments before I dig
further into that and propose a proper update.

One of the ARM helpers (sub with flag settings) has been
converted to TCG and uses setcond to compute carry.

setcond has been implemented only for x86_64 TCG back-end.

On my TODO list:

  - document setcond in tcg/README
  - implement it in all backends
      * arm
      * hppa (not applicable according to Stuart Brady)
      * i386
      * ppc
      * ppc64
      * sparc
      * x86_64 (done and partly tested)
  - use it at least once in every frontend
  - setcondi
  - 64 bit setcond's
  - a variant that sets -1 instead of 1 for masking
  - provide a test

Please feel free to comment :-)


Laurent

setcond-1.patch
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