gcc-2.95 19990629 miscompiles makeinfo.c

[Alexander Sokolov <robocop at amur dot rosnet dot ru>]

Building the latest gcc-2.95 snapshot I encountered with miscompilation
of makeinfo which segfaulted in get_until() when attempting to make
cpp.info. Take a look at the part of C source from makeinfo.c

get_until (match, string)
     char *match, **string;
{
  int len, current_point, x, new_point, tem;
   
  current_point = x = input_text_offset;
  new_point = search_forward (match, input_text_offset);
   
  if (new_point < 0)
    new_point = size_of_input_text;
  ...

and the assembler code generated by gcc-2.95 19990629 with -O2
-fomit-frame-pointer -march=pentiumpro options:

get_until:
        subl $28,%esp
        pushl %ebp
        pushl %edi
        pushl %esi
        pushl %ebx
        movl 48(%esp),%ebx
        movl input_text_offset,%edi
        addl $-8,%esp
        pushl %edi
        pushl %ebx
        call search_forward
        addl $16,%esp

%eax now contains new_point returned by search_forward() which should be
compared to 0. The obvious way is cmpl $0,%eax or even testl %eax,%eax but
look what gcc generates instead:

        cmpl $0,28(%esp)
        cmovl size_of_input_text,%eax
        movl %eax,28(%esp)

This code is incorrect because 28(%esp) contains garbage but not
new_point. Note that both -O1 and -O3 generate the correct code.

--
Alexander Sokolov
System Administrator
ROSNET Komsomolsk-na-Amure
Tel./Fax: +7-095-737-6260