🚀 go-pugleaf

I am running GCC 2.3.1 on a Sun Sparcstation.  GCC was compiled with
"configure sun4".

When NEEDLESS_REMAINDER is not defined in the following function, GCC
optimizes away the computation of (temp % 33), but with NEEDLESS_REMAINDER
defined, the optimization doesn't happen.  Remainder is implemented in a
subroutine on my machine, so it's expensive.

If the xxx variable is assigned to a different register, the optimized
assembly code is always produced -- NEEDLESS_REMAINDER doesn't make a
difference.


% cat wow5.c
============


#ifdef NEEDLESS_REMAINDER
register long xxx asm ("%o0");
#endif


void *
foobar()
{
    long temp;
    
    temp = 1;
    temp = temp % 33;
    
    if (temp == 0)
	short_computation();
    else if (temp == 1)
	long_computation();
}



% gcc-2.3.1 -O -S wow5.c -v
===========================

Reading specs from /usr/local/lib/gcc-lib/sun4/2.3.1/specs
gcc version 2.3.1
 /usr/local/lib/gcc-lib/sun4/2.3.1/cpp -lang-c -v -undef -D__GNUC__=2 -Dsparc -Dsun -Dunix -D__sparc__ -D__sun__ -D__unix__ -D__sparc -D__sun -D__unix -D__OPTIMIZE__ wow5.c /usr/tmp/cca04461.i
GNU CPP version 2.3.1 (sparc)
 /usr/local/lib/gcc-lib/sun4/2.3.1/cc1 /usr/tmp/cca04461.i -quiet -dumpbase wow5.c -O -version -o wow5.s
GNU C version 2.3.1 (sparc) compiled by GNU C version 2.3.1.


% cat wow5.s
============

gcc2_compiled.:
.text
	.align 4
	.global _foobar
	.proc	0120
_foobar:
	!#PROLOGUE# 0
	save %sp,-136,%sp
	!#PROLOGUE# 1
	call _long_computation,0
	nop
	ret
	restore


% gcc-2.3.1 -O -S wow5.c -v -DNEEDLESS_REMAINDER
================================================

Reading specs from /usr/local/lib/gcc-lib/sun4/2.3.1/specs
gcc version 2.3.1
 /usr/local/lib/gcc-lib/sun4/2.3.1/cpp -lang-c -v -DNEEDLESS_REMAINDER -undef -D__GNUC__=2 -Dsparc -Dsun -Dunix -D__sparc__ -D__sun__ -D__unix__ -D__sparc -D__sun -D__unix -D__OPTIMIZE__ wow5.c /usr/tmp/cca04465.i
GNU CPP version 2.3.1 (sparc)
 /usr/local/lib/gcc-lib/sun4/2.3.1/cc1 /usr/tmp/cca04465.i -quiet -dumpbase wow5.c -O -version -o wow5.s
GNU C version 2.3.1 (sparc) compiled by GNU C version 2.3.1.
wow5.c:3: warning: call-clobbered register used for global register variable

thor [299]  cat wow5.x s
gcc2_compiled.:
.text
	.align 4
	.global _foobar
	.proc	0120
_foobar:
	!#PROLOGUE# 0
	save %sp,-136,%sp
	!#PROLOGUE# 1
	mov 1,%o1
	mov %o1,%o0
	call .rem,0
	mov 33,%o1
	call _long_computation,0
	nop
	ret
	restore