Quoting Hans-Peter Nilsson <h...@bitrange.com>:
On Fri, 23 Sep 2011, Joern Rennecke wrote:
Quoting "Paulo J. Matos" <pa...@matos-sorge.com>:
> My addition instruction sets all the flags. So I have:
This is annoying, but can be handled. Been there, done that.
dse.c needs a small patch, which I intend to submit sometime in the future.
Could you be persuaded to send it to the list as-is, right now?
Be sure to mark it work-in-progress, or someone might feel
compelled to review it. :)
Attached.
The issue with this patch is that we'll have to check if gen_add3_insn might
fail on any target, and also we have to identify on which targets it will
create an insn that clobbers potentially live hard registers
(like a flags register), and make the substitution fail in this case.
I.e. if in doubt, keep the dead store with the auto-increment.
But not fail for a target that knows what it clobbers in a
reload_in_progress / reload_completed add.
For Epiphany, the add will be expanded with a clobber of a fake hard register,
and this pattern is subject to various peephole2 patterns which usually
find a low-cost substitute.
The point of clobbering a fake hard register is to avoid having passes like
combine creating the pattern with the unresolved flag clobber problem.
The unoptimized add expands into a sequentially issued five-instruction
in order to save/restore the flags to a temp register, which in turn is
saved on the stack.
There are peephole2 patterns to use a constant directly rather than loading
it into a temp register, to clobber the flags register if it is free,
to move the add before an immediately preceding flag-setting instruction,
to find a possibility for a dummy post-modify load from / store to the stack
(for calculating a stack/frame based address), and to scavenge a temp
register to save the flags into without needing to save the temp register.
2011-09-18 Joern Rennecke <joern.renne...@embecosm.com>
* dse.c (emit_inc_dec_insn_before): Use gen_add3_insn / gen_move_insn.
Index: dse.c
===================================================================
--- dse.c (revision 2071)
+++ dse.c (revision 2072)
@@ -835,15 +835,15 @@ emit_inc_dec_insn_before (rtx mem ATTRIB
rtx op ATTRIBUTE_UNUSED,
rtx dest, rtx src, rtx srcoff, void *arg)
{
- rtx insn = (rtx)arg;
-
- if (srcoff)
- src = gen_rtx_PLUS (GET_MODE (src), src, srcoff);
+ rtx insn = (rtx) arg, new_insn;
/* We can reuse all operands without copying, because we are about
to delete the insn that contained it. */
-
- emit_insn_before (gen_rtx_SET (VOIDmode, dest, src), insn);
+ if (srcoff)
+ new_insn = gen_add3_insn (dest, src, srcoff);
+ else
+ new_insn = gen_move_insn (dest, src);
+ emit_insn_before (new_insn, insn);
return -1;
}
