On Sat, Dec 20, 2014 at 8:18 PM, Eric Botcazou <ebotca...@adacore.com> wrote:
>> As described both in the PR and patch comments, this patch fixes PR62151 by
>> setting right value to ELIM_I0/ELIM_I1 when distributing REG_DEAD notes from
>> i0/i1. It is said that distribute_notes had caused many bugs in the past.
>> I think it still has bug in it, as noted in the PR. This patch doesn't
>> touch distribute_notes because we are in stage3 and I want to have more
>> discussion on it.
>> Bootstrap and test on x86_64. aarch64 is ongoing. So is it ok?
>>
>> 2014-12-11 Bin Cheng <bin.ch...@arm.com>
>>
>> PR rtl-optimization/62151
>> * combine.c (try_combine): Reset elim_i0 and elim_i1 when
>> distributing notes from i0notes or i1notes, this time don't
>> check whether newi2pat sets i1dest or i0dest.
>
> The reasoning looks correct to me and the patch is certainly safe so it's OK
> on principle, but I think that we should avoid the duplication of predicates.
>
> Can you move the computation of the alternative elim_i1 & elim_i0 up to where
> the original ones are computed along with the explanation of why we care about
> newi2pat only for notes that were on I3 and I2? Something like:
>
> /* Compute which registers we expect to eliminate. newi2pat may be setting
> either i3dest or i2dest, so we must check it. */
> rtx elim_i2 = ((newi2pat && reg_set_p (i2dest, newi2pat))
> || i2dest_in_i2src || i2dest_in_i1src || i2dest_in_i0src
> || !i2dest_killed
> ? 0 : i2dest);
> /* For I1 we need to compute both local elimination and global elimination
> because i1dest may be the same as i3dest, in which case newi2pat may be
> setting i1dest. <big explanation of why this is needed> */
> rtx local_elim_i1 = (i1 == 0 || i1dest_in_i1src || i1dest_in_i0src
> || !i1dest_killed
> ? 0 : i1dest);
> rtx elim_i1 = (local_elim_i1 == 0
> || (newi2pat && reg_set_p (i1dest, newi2pat))
> ? 0 : i1dest);
> /* Likewise for I0. */
> rtx local_elim_i0 = (i0 == 0 || i0dest_in_i0src
> || !i0dest_killed
> ? 0 : i0dest);
> rtx elim_i0 = (local_elim_i0 == 0
> || (newi2pat && reg_set_p (i0dest, newi2pat))
> ? 0 : i0dest);
>
> --
> Eric Botcazou
Hi Eric,
Thanks for reviewing. Here comes the revised patch. Bootstrap and
test on x86_64, is it OK?
Thanks,
bin
2014-12-22 Bin Cheng <bin.ch...@arm.com>
PR rtl-optimization/62151
* combine.c (try_combine): New local variables local_elim_i1
and local_elim_i0. Set elim_i1 and elim_i0 using the local
version variables. Distribute notes from i0notes or i1notes
using the local variavbles.
gcc/testsuite/ChangeLog
2014-12-22 Bin Cheng <bin.ch...@arm.com>
PR rtl-optimization/62151
* gcc.c-torture/execute/pr62151.c: New test.
Index: gcc/testsuite/gcc.c-torture/execute/pr62151.c
===================================================================
--- gcc/testsuite/gcc.c-torture/execute/pr62151.c (revision 0)
+++ gcc/testsuite/gcc.c-torture/execute/pr62151.c (revision 0)
@@ -0,0 +1,41 @@
+/* PR rtl-optimization/62151 */
+
+int a, c, d, e, f, g, h, i;
+short b;
+
+int
+fn1 ()
+{
+ b = 0;
+ for (;;)
+ {
+ int j[2];
+ j[f] = 0;
+ if (h)
+ d = 0;
+ else
+ {
+ for (; f; f++)
+ ;
+ for (a = 0; a < 1; a++)
+ for (;;)
+ {
+ i = b & ((b ^ 1) & 83647) ? b : b - 1;
+ g = 1 ? i : 0;
+ e = j[0];
+ if (c)
+ break;
+ return 0;
+ }
+ }
+ }
+}
+
+int
+main ()
+{
+ fn1 ();
+ if (g != -1)
+ __builtin_abort ();
+ return 0;
+}
Index: gcc/combine.c
===================================================================
--- gcc/combine.c (revision 218855)
+++ gcc/combine.c (working copy)
@@ -4119,19 +4119,46 @@ try_combine (rtx_insn *i3, rtx_insn *i2, rtx_insn
rtx midnotes = 0;
int from_luid;
/* Compute which registers we expect to eliminate. newi2pat may be setting
- either i3dest or i2dest, so we must check it. Also, i1dest may be the
- same as i3dest, in which case newi2pat may be setting i1dest. */
+ either i3dest or i2dest, so we must check it. */
rtx elim_i2 = ((newi2pat && reg_set_p (i2dest, newi2pat))
|| i2dest_in_i2src || i2dest_in_i1src || i2dest_in_i0src
|| !i2dest_killed
? 0 : i2dest);
- rtx elim_i1 = (i1 == 0 || i1dest_in_i1src || i1dest_in_i0src
+ /* For i1, we need to compute both local elimination and global
+ elimination information with respect to newi2pat because i1dest
+ may be the same as i3dest, in which case newi2pat may be setting
+ i1dest. Global information is used when distributing REG_DEAD
+ note for i2 and i3, in which case it does matter if newi2pat sets
+ i1dest or not.
+
+ Local information is used when distributing REG_DEAD note for i1,
+ in which case it doesn't matter if newi2pat sets i1dest or not.
+ See PR62151, if we have four insns combination:
+ i0: r0 <- i0src
+ i1: r1 <- i1src (using r0)
+ REG_DEAD (r0)
+ i2: r0 <- i2src (using r1)
+ i3: r3 <- i3src (using r0)
+ ix: using r0
+ From i1's point of view, r0 is eliminated, no matter if it is set
+ by newi2pat or not. In other words, REG_DEAD info for r0 in i1
+ should be discarded.
+
+ Note local information only affects cases in which I2 is after I0/I1,
+ like "I1->I2->I3", "I0->I1->I2->I3" or "I0&I1->I2, I2->I3". For other
+ cases like "I0->I1, I1&I2->I3" or "I1&I2->I3", newi2pat will not set
+ i1dest or i0dest. */
+ rtx local_elim_i1 = (i1 == 0 || i1dest_in_i1src || i1dest_in_i0src
+ || !i1dest_killed
+ ? 0 : i1dest);
+ rtx elim_i1 = (local_elim_i1 == 0
|| (newi2pat && reg_set_p (i1dest, newi2pat))
- || !i1dest_killed
? 0 : i1dest);
- rtx elim_i0 = (i0 == 0 || i0dest_in_i0src
+ /* Same case as i1. */
+ rtx local_elim_i0 = (i0 == 0 || i0dest_in_i0src || !i0dest_killed
+ ? 0 : i0dest);
+ rtx elim_i0 = (local_elim_i0 == 0
|| (newi2pat && reg_set_p (i0dest, newi2pat))
- || !i0dest_killed
? 0 : i0dest);
/* Get the old REG_NOTES and LOG_LINKS from all our insns and
@@ -4300,10 +4327,10 @@ try_combine (rtx_insn *i3, rtx_insn *i2, rtx_insn
elim_i2, elim_i1, elim_i0);
if (i1notes)
distribute_notes (i1notes, i1, i3, newi2pat ? i2 : NULL,
- elim_i2, elim_i1, elim_i0);
+ elim_i2, local_elim_i1, local_elim_i0);
if (i0notes)
distribute_notes (i0notes, i0, i3, newi2pat ? i2 : NULL,
- elim_i2, elim_i1, elim_i0);
+ elim_i2, elim_i1, local_elim_i0);
if (midnotes)
distribute_notes (midnotes, NULL, i3, newi2pat ? i2 : NULL,
elim_i2, elim_i1, elim_i0);
