Re: Mainline bootstrap failure (revision 110017)

[Andreas Krebbel <krebbel1 at de dot ibm dot com>]

(I've sent this first to gcc-patches accidently :(
> Kenny thought it would be nice, rather than pass the actual bb info to free to the freeing function, to instead pass some random bitmap.
> 
> 
> The attached fixes *that*, but this just causes a crash deeper in trying to free some chains.
> 
> However, it looks like that is either caused by a double free, or because
>  we never null out pointers to things after we free the memory for what they are pointing to.
> 
Here is a reduced testcase failing with -O1:

__udivmodti4 ()
{
  unsigned long d0, a;

  for (a = 56; a > 0; a -= 8)
    if ((d0 & 0xff) != 0)
      break;

  for (a = 57; a > 0; a -= 7)
    if ((d0 & 0xff) != 0)
      break;
}

With your patch:

Program received signal SIGSEGV, Segmentation fault.
0x0000000080188d16 in bitmap_obstack_free (map=0x808dea80) at /build/gcc-4.2/gcc/bitmap.c:272
272           map->first = (void *)map->obstack->heads;
(gdb) bt
#0  0x0000000080188d16 in bitmap_obstack_free (map=0x808dea80) at /build/gcc-4.2/gcc/bitmap.c:272
#1  0x00000000802319fc in df_rd_free (dflow=0x808c9eb0) at /build/gcc-4.2/gcc/df-problems.c:1191
#2  0x000000008022a2b6 in df_finish1 (df=0x808d7db0) at /build/gcc-4.2/gcc/df-core.c:406
#3  0x00000000802914be in iv_analysis_done () at /build/gcc-4.2/gcc/loop-iv.c:1238
#4  0x00000000803d4a42 in estimate_probability (loops_info=0x3ffffcd9ce0)
    at /build/gcc-4.2/gcc/predict.c:844
#5  0x00000000803e699c in rest_of_handle_branch_prob () at /build/gcc-4.2/gcc/profile.c:1363

Without your patch:

Program received signal SIGSEGV, Segmentation fault.
0x0000000080188d16 in bitmap_obstack_free (map=0x808ca708) at /build/gcc-4.2/gcc/bitmap.c:272
272           map->first = (void *)map->obstack->heads;
(gdb) bt
#0  0x0000000080188d16 in bitmap_obstack_free (map=0x808ca708) at /build/gcc-4.2/gcc/bitmap.c:272
#1  0x00000000802307b0 in df_rd_free_bb_info (dflow=0x808c9eb0, bb=0x2000001ad80, vbb_info=0x808ca660)
    at /build/gcc-4.2/gcc/df-problems.c:853
#2  0x0000000080229cd6 in df_set_blocks (df=0x808d7db0, blocks=0x808ca5a0)
    at /build/gcc-4.2/gcc/df-core.c:373
#3  0x000000008028e2ac in iv_analysis_loop_init (loop=0x808d7ca0) at /build/gcc-4.2/gcc/loop-iv.c:267
#4  0x00000000803d3efa in predict_loops (loops_info=0x3ffff889ce0, rtlsimpleloops=1 '\001')
    at /build/gcc-4.2/gcc/predict.c:618
#5  0x00000000803d4a24 in estimate_probability (loops_info=0x3ffff889ce0)
    at /build/gcc-4.2/gcc/predict.c:842
#6  0x00000000803e6984 in rest_of_handle_branch_prob () at /build/gcc-4.2/gcc/profile.c:1363

Bye,

-Andreas-

> Index: df-core.c
> ===================================================================
> --- df-core.c	(revision 110017)
> +++ df-core.c	(working copy)
> @@ -292,6 +292,7 @@ are write-only operations.  
>  static struct df *ddf = NULL;
>  struct df *shared_df = NULL;
>  
> +static void * df_get_bb_info (struct dataflow *, unsigned int);
>  /*----------------------------------------------------------------------------
>    Functions to create, destroy and manipulate an instance of df.
>  ----------------------------------------------------------------------------*/
> @@ -370,7 +371,7 @@ df_set_blocks (struct df *df, bitmap blo
>  		  EXECUTE_IF_SET_IN_BITMAP (diff, 0, bb_index, bi)
>  		    {
>  		      basic_block bb = BASIC_BLOCK (bb_index);
> -		      (*dflow->problem->free_bb_fun) (dflow, bb, diff);
> +		      (*dflow->problem->free_bb_fun) (dflow, bb, df_get_bb_info (dflow, bb_index));
>  		    }
>  		}
>  	    }