Re: [PATCH] shut up warnings in bits/string2.h

[Jakub Jelinek <jakub at redhat dot com>]

On Tue, Dec 07, 1999 at 11:38:43PM -0800, Ulrich Drepper wrote:
> Jakub Jelinek <jakub@redhat.com> writes:
> 
> > This patch shuts up gcc 2.96 warnings about long switch expressions not
> > converted to int.
> 
> Well, rth commented that this might fail for long strings.  But those
> strings must be string constants, not actual strings.  And gcc (nor
> any other compiler) will have support for strings of more than 2^32
> character in length.  So it should be possible to apply the patch.

All the inlines where I changed this are invoked from macros which guard it
by something like this:
__builtin_constant_p (n) && (n) <= 16
where the length limit is 16 or 8 as far as I could see, so I don't see how
that could be a problem (the only problematic thing could be say
memcpy(p, "string", -4) because then n is builtin constant and is <= 16, but
that should be guarded by
__builtin_constant_p (n) && (n) <= 16U
).

> 
> > How does it work on other architectures?
> 
> Which functions?  The generic functions should perform quite good.
> The copying of constant strings work by moving immedate values which
> is much faster.

E.g.
#include <string.h>
void foo(char *p)
{
	strcpy(p, "strn");
}

gets compiled with -O2 -m32 by gcc 2.96 (but similarly by egcs 1.1.2) into:
foo:	save	%sp, -224, %sp
	sethi	%hi(.LLC0+1), %o0
	or	%o0, %lo(.LLC0+1), %o0
	add	%o0, -1, %o5
	sub	%o0, %o5, %o0
	cmp	%o0, 1
	bne	.LL145
	mov	%i0, %o0
	mov	115, %o1
	mov	116, %o2
	mov	114, %o3
	mov	110, %o4
	stb	%o1, [%fp-32]
	stb	%g0, [%fp-31]
	stb	%o1, [%fp-24]
	stb	%g0, [%fp-23]
	stb	%o1, [%fp-48]
	stb	%o2, [%fp-47]
	stb	%g0, [%fp-46]
	stb	%o1, [%fp-40]
	stb	%o2, [%fp-39]
	stb	%g0, [%fp-38]
	stb	%o1, [%fp-64]
	stb	%o2, [%fp-63]
	stb	%o3, [%fp-62]
	stb	%g0, [%fp-61]
	stb	%o1, [%fp-56]
	stb	%o2, [%fp-55]
	stb	%o3, [%fp-54]
	stb	%g0, [%fp-53]
	stb	%o1, [%fp-80]
	stb	%o2, [%fp-79]
	stb	%o3, [%fp-78]
	stb	%o4, [%fp-77]
	stb	%g0, [%fp-76]
	stb	%o1, [%fp-72]
	stb	%o2, [%fp-71]
	stb	%o3, [%fp-70]
	stb	%o4, [%fp-69]
	stb	%g0, [%fp-68]
	ldub	[%o5+5], %o7
	mov	%o1, %l0
	stb	%o1, [%fp-96]
	stb	%o2, [%fp-95]
	stb	%o3, [%fp-94]
	stb	%o4, [%fp-93]
	stb	%g0, [%fp-92]
	stb	%g0, [%fp-91]
	stb	%o1, [%fp-88]
	stb	%o2, [%fp-87]
	stb	%o3, [%fp-86]
	stb	%o4, [%fp-85]
	stb	%g0, [%fp-84]
	stb	%g0, [%fp-83]
	stb	%o1, [%fp-112]
	stb	%o2, [%fp-111]
	stb	%o3, [%fp-110]
	stb	%o4, [%fp-109]
	stb	%g0, [%fp-108]
	stb	%o7, [%fp-107]
	stb	%g0, [%fp-106]
	stb	%o1, [%fp-104]
	stb	%o2, [%fp-103]
	stb	%o3, [%fp-102]
	stb	%o4, [%fp-101]
	stb	%g0, [%fp-100]
	stb	%o7, [%fp-99]
	stb	%g0, [%fp-98]
	ldub	[%o5+6], %l1
	mov	%o2, %g3
	ldub	[%fp-68], %o0
	stb	%o1, [%fp-120]
	stb	%o2, [%fp-119]
	stb	%o3, [%fp-118]
	stb	%o4, [%fp-117]
	stb	%o7, [%fp-115]
	stb	%l1, [%fp-114]
	mov	%o3, %g2
	mov	%o4, %o5
	stb	%o0, [%i0+4]
	stb	%l0, [%i0]
	stb	%g3, [%i0+1]
	stb	%g2, [%i0+2]
	stb	%o5, [%i0+3]
	stb	%o1, [%fp-128]
	stb	%o2, [%fp-127]
	stb	%o3, [%fp-126]
	stb	%o4, [%fp-125]
	stb	%g0, [%fp-124]
	stb	%o7, [%fp-123]
	stb	%l1, [%fp-122]
	stb	%g0, [%fp-121]
	stb	%g0, [%fp-116]
	b	.LL144
	stb	%g0, [%fp-113]
.LL145:	mov	%o5, %o1
	call	memcpy, 0
	mov	5, %o2
.LL144:	ret
	restore

while compiling it with the same compiler with -O2 -D__NO_STRING_INLINES
turns into (and similarly with egcs 1.1.2):
foo:	sethi	%hi(.LLC0), %g2
	ldub	[%g2+%lo(.LLC0)], %g3
	or	%g2, %lo(.LLC0), %g2
	stb	%g3, [%o0]
	ldub	[%g2+1], %g3
	stb	%g3, [%o0+1]
	ldub	[%g2+2], %o1
	stb	%o1, [%o0+2]
	ldub	[%g2+3], %g3
	stb	%g3, [%o0+3]
	ldub	[%g2+4], %o1
	retl
	stb	%o1, [%o0+4]

I haven't yet investigated what's the problem, but some string2.h inlines
work as expected (e.g. memset).

Cheers,
    Jakub
___________________________________________________________________
Jakub Jelinek | jakub@redhat.com | http://sunsite.mff.cuni.cz/~jj
Linux version 2.3.18 on a sparc64 machine (1343.49 BogoMips)
___________________________________________________________________