Re: optimization/10185: [3.3/3.4 regression] Wrong code with 3-int-structs & optimization

[Glen Nakamura <glen@imodulo.com>]

The following reply was made to PR optimization/10185; it has been noted by GNATS.

From: Glen Nakamura <glen@imodulo.com>
To: gcc-gnats@gcc.gnu.org, gcc-bugs@gcc.gnu.org, rassahah@neofonie.de
Cc:  
Subject: Re: optimization/10185: [3.3/3.4 regression] Wrong code with 3-int-structs & optimization
Date: Fri, 21 Mar 2003 22:13:39 -1000

 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=10185
 
 Aloha,
 This bug has similar symptoms to PR opt/10087.  The gcse pass generates
 the following code (notice insn 106 is redundant to insn 103):
 
 (insn 22 88 103 3 0x4014b764 (parallel [
             (set (reg/s:SI 65)
                 (plus:SI (reg:SI 79)
                     (const_int -1 [0xffffffff])))
             (clobber (reg:CC 17 flags))
         ]) 146 {*addsi_1} (nil)
     (nil))
 
 (insn 103 22 23 3 (nil) (set (reg:SI 79)
         (reg/s:SI 65)) 38 {*movsi_1} (nil)
     (nil))
 
 (insn 23 103 106 3 0x4014b764 (set (mem/f:SI (plus:SI (reg/f:SI 20 frame)
                 (const_int -4 [0xfffffffc])) [5 S4 A32])
         (reg/s:SI 65)) 38 {*movsi_1} (nil)
     (expr_list:REG_EQUAL (plus:SI (reg:SI 67)
             (const_int -1 [0xffffffff]))
         (nil)))
 
 (insn 106 23 25 3 (nil) (set (reg:SI 79)
         (reg/s:SI 65)) 38 {*movsi_1} (nil)
     (nil))
 
 The loop pass then considers insn 103 and insn 106 as places where biv 79
 is incremented.  This is incorrect since insn 106 sets reg 76 to the same
 value as insn 103.  Now during strength reduction, the giv is incremented
 after insn 103 and insn 106 resulting in a delta that is twice the correct
 value.  This test case passes with the patch from:
 http://gcc.gnu.org/ml/gcc-patches/2003-03/msg01932.html
 
 - glen