[Bug middle-end/18293] New: Redundant copy operation introduced by expand

[Bug middle-end/18293] New: Redundant copy operation introduced by expand

[steven at gcc dot gnu dot org]

Given this piece of code, 
 
struct deferred_access; 
extern struct deferred_access *D25481; 
struct deferred_access * 
foo (void) 
{ 
  return (struct deferred_access *) ((long unsigned int) D25481 * 16); 
} 
 
 
which generates on i686 in .00.expand (-fdump-rtl-expand-details): 
 
 
;; return (struct deferred_access *) ((long unsigned int) (int) D25481 * 16) 
(insn 10 9 11 (set (reg:SI 60) 
        (mem/f/i:SI (symbol_ref:SI ("D25481") [flags 0x40] <var_decl 
0x401d489c D25481>) [2 D25481+0 S4 A32])) -1 (nil) 
    (nil)) 
 
(insn 11 10 12 (set (reg:SI 61) 
        (reg:SI 60)) -1 (nil) 
    (nil)) 
 
(insn 12 11 13 (parallel [ 
            (set (reg:SI 62) 
                (ashift:SI (reg:SI 61) 
                    (const_int 4 [0x4]))) 
            (clobber (reg:CC 17 flags)) 
        ]) -1 (nil) 
    (expr_list:REG_EQUAL (mult:SI (reg:SI 60) 
            (const_int 16 [0x10])) 
        (nil))) 
 
(insn 13 12 14 (set (reg:SI 58 [ <result> ]) 
        (reg:SI 62)) -1 (nil) 
    (nil)) 
 
 
 
Notice the unnecessary copy insn 11: 
(insn 11 10 12 (set (reg:SI 61) (reg:SI 60)) -1 (nil) (nil)) 
 
Is there some way, oh RTL gurus tell me!, to avoid introducing this 
garbage RTL that only introduces work for the RTL optimizers?

-- 
           Summary: Redundant copy operation introduced by expand
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: steven at gcc dot gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org,sayle at gcc dot gnu dot
                    org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18293

[Bug middle-end/18293] Redundant copy operation introduced by expand

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-11-03 22:58 -------
Confirmed.  This is related to casts somehow.
Also this happens on 3.3 which is even more funny and just show the deficiencies in the expanders 
which no one noticed before.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |minor
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
           Keywords|                            |compile-time-hog, memory-
                   |                            |hog, missed-optimization
      Known to fail|                            |3.3 4.0.0
   Last reconfirmed|0000-00-00 00:00:00         |2004-11-03 22:58:55
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18293

[Bug middle-end/18293] Redundant copy operation introduced by expand

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-11-04 17:20 -------
I am testing this patch (which is a modified version of the one which you gave me), it should help -O0 
compile time as we no longer have an extra INSN which gets removed right after the register allocator:
Index: expmed.c
===============================================================
====
RCS file: /cvs/gcc/gcc/gcc/expmed.c,v
retrieving revision 1.200
diff -u -p -r1.200 expmed.c
--- expmed.c	21 Oct 2004 10:51:00 -0000	1.200
+++ expmed.c	4 Nov 2004 16:55:46 -0000
@@ -2638,7 +2638,10 @@ expand_mult_const (enum machine_mode mod
     }
   else if (alg->op[0] == alg_m)
     {
-      accum = copy_to_mode_reg (mode, op0);
+      if (REG_P (op0) && GET_MODE (op0) == mode && alg->ops == 2)
+        accum = op0;
+      else
+        accum = copy_to_mode_reg (mode, op0);
       val_so_far = 1;
     }
   else


-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pinskia at gcc dot gnu dot
                   |                            |org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18293

[Bug middle-end/18293] Redundant copy operation introduced by expand

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-11-09 21:33 -------
Patch posted here: <http://gcc.gnu.org/ml/gcc-patches/2004-11/msg00775.html>.  Mine.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |pinskia at gcc dot gnu dot
                   |dot org                     |org
             Status|NEW                         |ASSIGNED
           Keywords|                            |patch


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18293

[Bug middle-end/18293] Redundant copy operation introduced by expand

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-11-12 15:35 -------
Note if we change this we have to look at the IV-OPT cost analysis mechanism and retune it to be more 
correct as we will miss some optimizations.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|pinskia at gcc dot gnu dot  |unassigned at gcc dot gnu
                   |org                         |dot org
             Status|ASSIGNED                    |NEW


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18293

[Bug middle-end/18293] Redundant copy operation introduced by expand

[cvs-commit at gcc dot gnu dot org]

------- Additional Comments From cvs-commit at gcc dot gnu dot org  2004-12-08 02:15 -------
Subject: Bug 18293

CVSROOT:	/cvs/gcc
Module name:	gcc
Changes by:	sayle@gcc.gnu.org	2004-12-08 02:15:39

Modified files:
	gcc            : ChangeLog expmed.c loop.c 

Log message:
	PR middle-end/18293
	* expmed.c (EXACT_POWER_OF_2_OR_ZERO_P): Move definition earlier.
	(expand_mult): Special case powers of two to avoid synth_mult.
	* loop.c (product_cheap_p): Handle case where expand_mult does
	require/generate any instructions (i.e. multiplication by zero).

Patches:
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/ChangeLog.diff?cvsroot=gcc&r1=2.6742&r2=2.6743
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/expmed.c.diff?cvsroot=gcc&r1=1.211&r2=1.212
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/loop.c.diff?cvsroot=gcc&r1=1.516&r2=1.517



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18293

[Bug middle-end/18293] Redundant copy operation introduced by expand

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-12-08 02:29 -------
Fixed.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18293

[Bug middle-end/18293] Redundant copy operation introduced by expand

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.0.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18293