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Re: alpha combine/schedule conflict
- To: Jim Wilson <wilson at cygnus dot com>
- Subject: Re: alpha combine/schedule conflict
- From: Richard Henderson <rth at cygnus dot com>
- Date: Tue, 28 Oct 1997 11:11:09 -0800
- Cc: egcs at cygnus dot com
- References: <19971027142124.62972@dot.cygnus.com> <199710280527.VAA04443@cygnus.com>
- Reply-To: Richard Henderson <rth at cygnus dot com>
On Mon, Oct 27, 1997 at 09:27:50PM -0800, Jim Wilson wrote:
> This is a known problem. Combine is emitting a lot of USE insns that it
> should not be. I tried coming up with a patch, but it is known to be
> incomplete/incorrect.
It looks to me that it solved the USE problem in the test case, but
exposed a new bug also related to REG_DEAD notes. For the test case
I posted at the beginning of this thread I get
(insn 201 199 202 (set (reg/v:DI 71)
(const_int -1)) 252 {movdi-1} (nil)
(nil))
(insn 202 201 205 (set (reg/v:DI 71)
(plus:DI (reg/v:DI 71)
(const_int 536870912))) 7 {adddi3} (insn_list 201 (nil))
(expr_list:REG_DEAD (reg/v:DI 71)
(expr_list:REG_EQUAL (const_int 536870911)
(nil))))
[...]
(insn 209 207 210 (set (reg:DI 137)
(leu:DI (reg:DI 135)
(reg/v:DI 71))) 131 {subdf3+4} (insn_list 202 (insn_list 207 (nil)))
(expr_list:REG_DEAD (reg/v:DI 71)
(nil)))
It appears to be simply due to incomplete checking for elim_i1. The
attached patch (combined with yours because I'm lazy) solves the problem
for the test case. A sanity three-stage is still going, but I'll let
you know.
r~
Tue Oct 28 01:56:39 1997 Richard Henderson <rth@cygnus.com>
* combine.c (try_combine): Don't elim_i1 when it is used in i2src.
Tue Sep 23 12:57:35 1997 Jim Wilson <wilson@cygnus.com>
* combine.c (try_combine): When setting elim_i2, check whether newi2pat
sets i2dest. When calling distribute_notes for i3dest_killed, pass
elim_i2 and elim_i1.
Index: combine.c
===================================================================
RCS file: /cvs/cvsfiles/egcs/gcc/combine.c,v
retrieving revision 1.4
diff -u -p -d -r1.4 combine.c
--- combine.c 1997/10/16 22:06:43 1.4
+++ combine.c 1997/10/28 18:54:33
@@ -1246,6 +1246,7 @@ try_combine (i3, i2, i1)
rtx i2pat;
/* Indicates if I2DEST or I1DEST is in I2SRC or I1_SRC. */
int i2dest_in_i2src = 0, i1dest_in_i1src = 0, i2dest_in_i1src = 0;
+ int i1dest_in_i2src = 0;
int i1_feeds_i3 = 0;
/* Notes that must be added to REG_NOTES in I3 and I2. */
rtx new_i3_notes, new_i2_notes;
@@ -1431,6 +1432,7 @@ try_combine (i3, i2, i1)
i2dest_in_i2src = reg_overlap_mentioned_p (i2dest, i2src);
i1dest_in_i1src = i1 && reg_overlap_mentioned_p (i1dest, i1src);
i2dest_in_i1src = i1 && reg_overlap_mentioned_p (i2dest, i1src);
+ i1dest_in_i2src = i1 && reg_overlap_mentioned_p (i1dest, i2src);
/* See if I1 directly feeds into I3. It does if I1DEST is not used
in I2SRC. */
@@ -2141,10 +2143,12 @@ try_combine (i3, i2, i1)
rtx i3links, i2links, i1links = 0;
rtx midnotes = 0;
register int regno;
- /* Compute which registers we expect to eliminate. */
- rtx elim_i2 = (newi2pat || i2dest_in_i2src || i2dest_in_i1src
+ /* 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
? 0 : i2dest);
- rtx elim_i1 = i1 == 0 || i1dest_in_i1src ? 0 : i1dest;
+ rtx elim_i1 = i1 == 0 || i1dest_in_i1src || i1dest_in_i2src ? 0 : i1dest;
/* Get the old REG_NOTES and LOG_LINKS from all our insns and
clear them. */
@@ -2305,7 +2309,7 @@ try_combine (i3, i2, i1)
distribute_notes (gen_rtx (EXPR_LIST, REG_DEAD, i3dest_killed,
NULL_RTX),
NULL_RTX, i3, newi2pat ? i2 : NULL_RTX,
- NULL_RTX, NULL_RTX);
+ elim_i2, elim_i1);
}
/* For I2 and I1, we have to be careful. If NEWI2PAT exists and sets