Re: combine.c accesses uninitialized variable :-(

[Andreas Jaeger <aj at suse dot de>]

>>>>> Andreas Jaeger writes:

 > The last patch to combine accesses uninitialized memory.  I noticed
 > this since compilation of glibc produced an ICE.

 > Here's a patch that also fixes another problem (a prototype declared
 > with static but the function doesn't have static).  


 > Ok to install if it passes bootstrap and checking?

 > Andreas 

 > 2001-01-12  Andreas Jaeger  <aj@suse.de>

 > 	* combine.c (reversed_comparison): Fix typo in last patch.
 > 	(combine_reversed_comparison_code): Make static to follow
 > 	prototype declaration.

 > Index: combine.c
 > ===================================================================
 > RCS file: /cvs/gcc/egcs/gcc/combine.c,v
 > retrieving revision 1.174
 > diff -u -r1.174 combine.c
 > --- combine.c	2001/01/11 23:10:30	1.174
 > +++ combine.c	2001/01/12 08:42:28
 > @@ -11123,7 +11123,7 @@
 >  
 >  /* Like jump.c' reversed_comparison_code, but use combine infrastructure for
 >     searching backward.  */
 > -enum rtx_code
 > +static enum rtx_code
 >  combine_reversed_comparison_code (exp)
 >       rtx exp;
 >  {
 > @@ -11135,7 +11135,7 @@
 >       return code1;
 >     /* Otherwise try and find where the condition codes were last set and
 >        use that.  */
 > -   x = get_last_value (XEXP (x, 0));
 > +   x = get_last_value (XEXP (exp, 0));
 >     if (GET_CODE (x) != COMPARE)
 >       return UNKNOWN;
 >     return reversed_comparison_code_parts (GET_CODE (exp),

This patch doesn't fix the problem :-(

(gdb) r -fpreprocessed init-first.i -quiet -dumpbase init-first.c -march=pentiumpro -mcpu=i686 -g -O3 -Wall -Wbad-function-cast -Wcomment -Wcomments -Winline -Wmissing-declarations -Wmissing-format-attribute -Wmissing-noreturn -Wmissing-prototypes -Wmultichar -Wsign-compare -Wstrict-prototypes -Wtrigraphs -Wwrite-strings -version -freorder-blocks -fssa -fkeep-inline-functions -o init-first.s
GNU CPP version 2.97 20010111 (experimental) (cpplib) (i386 Linux/ELF)
GNU C version 2.97 20010111 (experimental) (i686-pc-linux-gnu)
        compiled by GNU C version 2.97 20010111 (experimental).

Breakpoint 1, combine_reversed_comparison_code (exp=0x40325130)
    at /cvs/gcc/gcc/combine.c:11138
11138      x = get_last_value (XEXP (exp, 0));
(gdb) p exp
$3 = 0x40325130
(gdb) p *exp
$4 = {code = LT, mode = VOIDmode, jump = 0, call = 0, unchanging = 0, volatil = 0, 
  in_struct = 0, used = 1, integrated = 0, frame_related = 0, fld = {{rtwint = 1077039360, 
      rtint = 1077039360, rtuint = 1077039360, rtstr = 0x40325100 "9", rtx = 0x40325100, 
      rtvec = 0x40325100, rttype = 1077039360, rt_addr_diff_vec_flags = {min_align = 0, 
        base_after_vec = 1, min_after_vec = 0, max_after_vec = 0, min_after_base = 0, 
        max_after_base = 1, offset_unsigned = 0, 1, scale = 50}, rt_cselib = 0x40325100, 
      rtbit = 0x40325100, rttree = 0x40325100, bb = 0x40325100}}}
(gdb) p x
$5 = 0x34
(gdb) n
11139      if (GET_CODE (x) != COMPARE)
(gdb) p x
$6 = 0x0
(gdb) bt
#0  combine_reversed_comparison_code (exp=0x40325130) at /cvs/gcc/gcc/combine.c:11139
#1  0x81aee3e in simplify_if_then_else (x=0x40325170) at /cvs/gcc/gcc/combine.c:4644
#2  0x81ad689 in combine_simplify_rtx (x=0x40325170, op0_mode=VOIDmode, last=0, in_dest=0)
    at /cvs/gcc/gcc/combine.c:4482
#3  0x81acba0 in subst (x=0x40325170, from=0x40325140, to=0x4018e3f8, in_dest=0, 
    unique_copy=0) at /cvs/gcc/gcc/combine.c:3466
#4  0x81acc2a in subst (x=0x40325180, from=0x40325140, to=0x4018e3f8, in_dest=0, 
    unique_copy=0) at /cvs/gcc/gcc/combine.c:3436
#5  0x81a9b8f in try_combine (i3=0x40323f40, i2=0x40323f00, i1=0x0, 
    new_direct_jump_p=0xbfffeea4) at /cvs/gcc/gcc/combine.c:1935
#6  0x81a86a0 in combine_instructions (f=0x4030d4a0, nregs=131) at /cvs/gcc/gcc/combine.c:635
#7  0x8097481 in rest_of_compilation (decl=0x4031c3a8) at /cvs/gcc/gcc/toplev.c:3290
#8  0x8062a35 in c_expand_body (fndecl=0x4031c3a8, nested_p=0) at /cvs/gcc/gcc/c-decl.c:6699
#9  0x8062721 in finish_function (nested=0) at /cvs/gcc/gcc/c-decl.c:6620
#10 0x804a126 in yyparse_1 () at /usr/share/bison.simple:323
#11 0x8095f3d in compile_file (name=0x8383d51 "init-first.i") at /cvs/gcc/gcc/toplev.c:2374
#12 0x8099b2c in main (argc=30, argv=0xbffff55c) at /cvs/gcc/gcc/toplev.c:4872
#13 0x40042baf in __libc_start_main () from /lib/libc.so.6

The file init-first.i is available at
ftp.suse.com/pub/people/aj/init-first.i.

Andreas
-- 
 Andreas Jaeger
  SuSE Labs aj@suse.de
   private aj@arthur.inka.de
    http://www.suse.de/~aj