Bad C code generation, egcs-980914, short example

[Paul Henning]

Reading specs from
/usr/local/app/egcs-19980914/lib/gcc-lib/i686-pc-linux-gnu/egcs-2.92.07/specs
gcc version egcs-2.92.07 19980914 (gcc2 ss-980609 experimental)

egcs-980914 is miscompiling teTeX-0.9 (a really nice TeX/LaTeX/etc
distribution), and I isolated the problem to the following bit of
preprocessed C code:

# 1 "ha.c"
extern long curcs;
extern long curtok;
void gettoken(void);

void getrtoken (void) 
{
 lab20: 
  do { gettoken(); } while(curtok == 2592);
  if (curcs == 0) goto lab20 ;
} 


when this is compiled with: gcc -v -O2 -S ha.i
I get the following code:

gcc2_compiled.:
.text
	.align 4
.globl getrtoken
	.type	 getrtoken,@function
getrtoken:
	pushl %ebp
	movl %esp,%ebp
	pushl %ebx
.L2:
	movl curtok,%ebx
	.p2align 4,,7
.L3:
	call gettoken
	cmpl $2592,%ebx
	je .L3

(plus some more stuff)

The problem is that %ebx is getting loaded with the value of curtok
before the call to gettoken.  Of course, gettoken is changing curtok
as a side-effect, and the whole comparison is get hosed.  Adding
--no-force-mem makes the problem go away by not doing the compare in
the register.

Thanks,
Paul Henning
paul-henning@uiowa.edu		http://www.cs.uiowa.edu/~phenning