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Re: [PATCH] Fix PR 91708
On 9/12/19 10:08 AM, Richard Biener wrote:
> On Wed, 11 Sep 2019, Bernd Edlinger wrote:
>
>> On 9/11/19 8:30 PM, Richard Biener wrote:
>
> More like the following? I wonder if we can assert that
> MEM_NOTRAP_P () are equal (see all the for_gcse checks in exp_equiv_p).
> But as said earlier I wonder in which cases a replacement is
> profitable at all - thus, if a
>
> else if (MEM_P (trial))
> /* Do not replace anything with a MEM. */
> ;
>
Yes, I like that better, since there is essentially nothing stopping
it from replacing a REG with a MEM, except the rtxcost function, maybe.
It turned out that the previous version got into an endless loop here,
since the loop termination happens when replacing MEM by itself, except
when something else terminates the search.
So how about this?
The only possible MEM->MEM transformations are now:
- replacing trial = dest (result mov dest, dest; which is a no-op insn)
- replacing trial = src (which is a no-op transformation, and exits the loop)
Therefore the overlapping mem move handling no longer necessary.
Bootstrap and reg-tested on x86_64-pc-linux-gnu.
Is it OK for trunk?
Thanks
Bernd.
2019-09-12 Bernd Edlinger <bernd.edlinger@hotmail.de>
PR middle-end/91708
* cse.c (cse_insn): Do not replace anything with a
MEM.
--- gcc/cse.c.orig 2019-07-24 21:21:53.590065924 +0200
+++ gcc/cse.c 2019-09-12 12:50:18.566801155 +0200
@@ -5238,23 +5238,6 @@ cse_insn (rtx_insn *insn)
src_elt_cost = MAX_COST;
}
- /* Avoid creation of overlapping memory moves. */
- if (MEM_P (trial) && MEM_P (dest) && !rtx_equal_p (trial, dest))
- {
- rtx src, dest;
-
- /* BLKmode moves are not handled by cse anyway. */
- if (GET_MODE (trial) == BLKmode)
- break;
-
- src = canon_rtx (trial);
- dest = canon_rtx (SET_DEST (sets[i].rtl));
-
- if (!MEM_P (src) || !MEM_P (dest)
- || !nonoverlapping_memrefs_p (src, dest, false))
- break;
- }
-
/* Try to optimize
(set (reg:M N) (const_int A))
(set (reg:M2 O) (const_int B))
@@ -5385,6 +5368,12 @@ cse_insn (rtx_insn *insn)
/* Do nothing for this case. */
;
+ /* Do not replace anything with a MEM, except the replacement
+ is a no-op. This allows this loop to terminate. */
+ else if (MEM_P (trial) && !rtx_equal_p (trial, SET_SRC(sets[i].rtl)))
+ /* Do nothing for this case. */
+ ;
+
/* Look for a substitution that makes a valid insn. */
else if (validate_unshare_change (insn, &SET_SRC (sets[i].rtl),
trial, 0))