Re: optimization/8634: [3.2/3.3 regression] incorrect code for inlining of memcpy under -O2

Re: optimization/8634: [3.2/3.3 regression] incorrect code for inlining of memcpy under -O2

[bangerth]

Old Synopsis: incorrect inlining of memcpy under -O2
New Synopsis: [3.2/3.3 regression] incorrect code for inlining of memcpy under -O2

State-Changed-From-To: open->analyzed
State-Changed-By: bangerth
State-Changed-When: Wed Dec  4 14:31:57 2002
State-Changed-Why:
    Confirmed. This program
    ----------------------------
    #include <stdio.h>
    #include <string.h>
    
    int main()
    {
      char* buffer = new char[8];
      const char head[8] = {
        'A', 'B', 'C', 'D',
        'E', 'F', 'G', 'H'
      };
      memcpy(buffer,head,8);
      for(int i=0;i<8;i++)
        printf ("[%u] = %c, %c\n", i, head[i], buffer[i]);
      return 0;
    }
    --------------------------------
    yields with 3.2.2pre, 3.3pre, and 2.95 respectively:
    
    tmp/g> /home/bangerth/bin/gcc-3.2.2-pre/bin/c++ -O2 bug.cc  &&  ./a.out
    [0] = A, A
    [1] = B,
    [2] = C,
    [3] = D,
    [4] = E, E
    [5] = F, F
    [6] = G, G
    [7] = H, H
    
    
    tmp/g> /home/bangerth/bin/gcc-3.3-pre/bin/c++ -O2 bug.cc  &&  ./a.out
    [0] = A, A
    [1] = B,
    [2] = C,
    [3] = D,
    [4] = E, E
    [5] = F, F
    [6] = G, G
    [7] = H, H
    
    
    tmp/g> c++ -O2 bug.cc  &&  ./a.out
    [0] = A, A
    [1] = B, B
    [2] = C, C
    [3] = D, D
    [4] = E, E
    [5] = F, F
    [6] = G, G
    [7] = H, H
    
    
    That seems like a regression.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=8634

Re: optimization/8634: [3.2/3.3 regression] incorrect code for inlining of memcpy under -O2

[Glen Nakamura]

The following reply was made to PR optimization/8634; it has been noted by GNATS.

From: Glen Nakamura <glen@imodulo.com>
To: gcc-gnats@gcc.gnu.org, gcc-bugs@gcc.gnu.org
Cc:  
Subject: Re: optimization/8634: [3.2/3.3 regression] incorrect code for inlining of memcpy under -O2
Date: Sun, 23 Mar 2003 18:07:39 +0000

 --wRRV7LY7NUeQGEoC
 Content-Type: text/plain; charset=us-ascii
 Content-Disposition: inline
 
 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=8634
 
 Attached is an extended test case for constant initializers.
 
 
 --wRRV7LY7NUeQGEoC
 Content-Type: text/plain; charset=us-ascii
 Content-Disposition: attachment; filename="pr8634.c"
 
 /* PR optimization/8634 */
 /* Contributed by Glen Nakamura <glen@imodulo.com> */
 
 extern void abort (void);
 
 struct foo {
   char a, b, c, d, e, f, g, h, i, j;
 };
 
 int test1 ()
 {
   const char X[8] = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H' };
   char buffer[8];
   __builtin_memcpy (buffer, X, 8);
   if (buffer[0] != 'A' || buffer[1] != 'B'
       || buffer[2] != 'C' || buffer[3] != 'D'
       || buffer[4] != 'E' || buffer[5] != 'F'
       || buffer[6] != 'G' || buffer[7] != 'H')
     abort ();
   return 0;
 }
 
 int test2 ()
 {
   const char X[10] = { 'A', 'B', 'C', 'D', 'E' };
   char buffer[10];
   __builtin_memcpy (buffer, X, 10);
   if (buffer[0] != 'A' || buffer[1] != 'B'
       || buffer[2] != 'C' || buffer[3] != 'D'
       || buffer[4] != 'E' || buffer[5] != '\0'
       || buffer[6] != '\0' || buffer[7] != '\0'
       || buffer[8] != '\0' || buffer[9] != '\0')
     abort ();
   return 0;
 }
 
 int test3 ()
 {
   const struct foo X = { a : 'A', c : 'C', e : 'E', g : 'G', i : 'I' };
   char buffer[10];
   __builtin_memcpy (buffer, &X, 10);
   if (buffer[0] != 'A' || buffer[1] != '\0'
       || buffer[2] != 'C' || buffer[3] != '\0'
       || buffer[4] != 'E' || buffer[5] != '\0'
       || buffer[6] != 'G' || buffer[7] != '\0'
       || buffer[8] != 'I' || buffer[9] != '\0')
     abort ();
   return 0;
 }
 
 int test4 ()
 {
   const struct foo X = { .b = 'B', .d = 'D', .f = 'F', .h = 'H' , .j = 'J' };
   char buffer[10];
   __builtin_memcpy (buffer, &X, 10);
   if (buffer[0] != '\0' || buffer[1] != 'B'
       || buffer[2] != '\0' || buffer[3] != 'D'
       || buffer[4] != '\0' || buffer[5] != 'F'
       || buffer[6] != '\0' || buffer[7] != 'H'
       || buffer[8] != '\0' || buffer[9] != 'J')
     abort ();
   return 0;
 }
 
 int main ()
 {
   test1 (); test2 (); test3 (); test4 ();
   return 0;
 }
 
 --wRRV7LY7NUeQGEoC--

Re: optimization/8634: [3.2/3.3 regression] incorrect code for inlining of memcpy under -O2

[Janis Johnson]

The following reply was made to PR optimization/8634; it has been noted by GNATS.

From: Janis Johnson <janis187@us.ibm.com>
To: gcc-gnats@gcc.gnu.org, gcc-prs@gcc.gnu.org, duchier@ps.uni-sb.de,
   gcc-bugs@gcc.gnu.org, nobody@gcc.gnu.org
Cc:  
Subject: Re: optimization/8634: [3.2/3.3 regression] incorrect code for inlining 
 of memcpy under -O2
Date: Mon, 23 Dec 2002 16:37:21 -0800

 The regression reported in PR optimization/8634 showed up
 starting with this patch (strange but true):
 
 Fri Dec 21 23:30:14 CET 2001  Jan Hubicka  <jh@suse.cz>
      * i386.h (TARGET_CPU_DEFAULT_pentium_mmx): New.
     (TARGET_CPU_DEFAULT_*): Renumber.
 
 I used this test case that Wolfgang provided.  It aborts
 when the wrong code is generated for -O2 on i686-linux:
 
 --------------
 /* incorrect code for inlining of memcpy under -O2 */
 
 #include <string.h>
 #include <stdlib.h>
 
 int
 main ()
 {
   int i;
   char buffer[8];
   const char head[8] =
     { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H' };
   memcpy (buffer, head, 8);
   for (i = 0; i < 8; i++)
     if (head[i] != buffer[i])
       abort ();
   return 0;
 }
 --------------
 
 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=8634
 
 
 

Re: optimization/8634: [3.2/3.3 regression] incorrect code for inlining of memcpy under -O2

[Glen Nakamura]

The following reply was made to PR optimization/8634; it has been noted by GNATS.

From: Glen Nakamura <glen@imodulo.com>
To: gcc-gnats@gcc.gnu.org, gcc-bugs@gcc.gnu.org
Cc:  
Subject: Re: optimization/8634: [3.2/3.3 regression] incorrect code for inlining of memcpy under -O2
Date: Mon, 9 Dec 2002 22:20:00 -1000

 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=8634
 
 Additional analysis of the problem and work-around patch posted at:
 http://gcc.gnu.org/ml/gcc-patches/2002-12/msg00533.html
 
 GCC developers with more experience should decide whether or not
 const initializers should be flagged as RTX_UNCHANGING, and if so then
 the cases that generate multiple sets need to be fixed...
 
 - glen