On Wed, 6 Nov 2024, Jakub Jelinek wrote:
> Hi!
>
> As mentioned in the "inline asm: Add new constraint for symbol definitions"
> patch description, while the c operand modifier is documented to:
> Require a constant operand and print the constant expression with no
> punctuation.
> it actually doesn't do that with -fpic at least on some targets and
> has been behaving that way for at least 3 decades.
> It prints the operand using output_addr_const if CONSTANT_ADDRESS_P is true,
> but CONSTANT_ADDRESS_P can do all sorts of target specific checks.
> And if it is false, it falls back to output_operand (operands[opnum], 'c');
> which will on various targets just result in an error that it is invalid
> modifier letter (weird because it is documented), on others like x86 or
> alpha will handle the operand in some weird way if it is a comparison
> and otherwise complain the argument isn't a comparison, on others like
> arm perhaps do what the user wanted.
>
> As I wrote, we are pretty much out of modifier letters because some targets
> use a lot of them, and almost out of % punctuation chars (I think ` is left)
> but right now punctuation chars aren't normally followed by operand number
> anyway.
>
> So, the following patch takes one of the generic letters (c) and adds an
> extra modifier char after it, I chose cc, which behaves like c but just
> always uses output_addr_const instead of falling back to the machine
> dependent code.
IMO quite reasonable.
Thus OK if there are no complaints.
Thanks,
Richard.
> 2024-11-06 Jakub Jelinek <ja...@redhat.com>
>
> * final.cc (output_asm_insn): Add support for cc operand modifier.
> * doc/extend.texi (Generic Operand Modifiers): Document cc operand
> modifier.
> * doc/md.texi (@samp{:} in constraint): Mention the cc operand
> modifier and add small example.
>
> * c-c++-common/toplevel-asm-4.c: Don't use -fno-pie option.
> Use cc modifier instead of c.
> (v, w): Add extern keyword.
> * c-c++-common/toplevel-asm-6.c: New test.
>
> --- gcc/final.cc.jj 2024-11-06 10:23:21.214728021 +0100
> +++ gcc/final.cc 2024-11-06 11:02:40.406413277 +0100
> @@ -3492,7 +3492,10 @@ output_asm_insn (const char *templ, rtx
> int letter = *p++;
> unsigned long opnum;
> char *endptr;
> + int letter2 = 0;
>
> + if (letter == 'c' && *p == 'c')
> + letter2 = *p++;
> opnum = strtoul (p, &endptr, 10);
>
> if (endptr == p)
> @@ -3506,7 +3509,7 @@ output_asm_insn (const char *templ, rtx
> output_address (VOIDmode, operands[opnum]);
> else if (letter == 'c')
> {
> - if (CONSTANT_ADDRESS_P (operands[opnum]))
> + if (letter2 == 'c' || CONSTANT_ADDRESS_P (operands[opnum]))
> output_addr_const (asm_out_file, operands[opnum]);
> else
> output_operand (operands[opnum], 'c');
> --- gcc/doc/extend.texi.jj 2024-11-06 10:23:21.220727937 +0100
> +++ gcc/doc/extend.texi 2024-11-06 11:09:46.433407349 +0100
> @@ -12113,6 +12113,11 @@ The following table shows the modifiers
> @item @code{c}
> @tab Require a constant operand and print the constant expression with no
> punctuation.
> @tab @code{%c0}
> +@item @code{cc}
> +@tab Like @samp{%c} except try harder to print it with no punctuation.
> +@samp{%c} can e.g.@: fail to print constant addresses in position
> independent code on
> +some architectures.
> +@tab @code{%cc0}
> @item @code{n}
> @tab Like @samp{%c} except that the value of the constant is negated before
> printing.
> @tab @code{%n0}
> --- gcc/doc/md.texi.jj 2024-11-06 10:30:09.884948601 +0100
> +++ gcc/doc/md.texi 2024-11-06 11:12:51.893792814 +0100
> @@ -1510,6 +1510,13 @@ This constraint, allowed only in input o
> pattern defines specific function or variable symbol. The constraint
> shouldn't be mixed with other constraints on the same operand and
> the operand should be address of a function or non-automatic variable.
> +Best used with the @samp{cc} modifier when printing the operand, so that
> +even in position independent code it prints as a label.
> +
> +@smallexample
> +void foo (void);
> +asm (".globl %cc0; %cc0: ret" : : ":" (foo));
> +@end smallexample
>
> @cindex other register constraints
> @cindex extensible constraints
> --- gcc/testsuite/c-c++-common/toplevel-asm-4.c.jj 2024-11-06
> 10:30:09.888948544 +0100
> +++ gcc/testsuite/c-c++-common/toplevel-asm-4.c 2024-11-06
> 11:14:14.553627513 +0100
> @@ -1,9 +1,8 @@
> /* PR c/41045 */
> /* { dg-do compile } */
> /* { dg-options "-O0" } */
> -/* { dg-additional-options "-fno-pie" { target pie } } */
>
> -int v[42], w;
> +extern int v[42], w;
> void foo (void);
>
> -asm ("# %c0: %c1:" :: ":" (foo), ":" (v), ":" (&w));
> +asm ("# %cc0: %cc1:" :: ":" (foo), ":" (v), ":" (&w));
> --- gcc/testsuite/c-c++-common/toplevel-asm-6.c.jj 2024-11-06
> 11:13:44.342053423 +0100
> +++ gcc/testsuite/c-c++-common/toplevel-asm-6.c 2024-11-06
> 11:14:27.548444315 +0100
> @@ -0,0 +1,9 @@
> +/* PR c/41045 */
> +/* { dg-do compile } */
> +/* { dg-options "-O0" } */
> +/* { dg-additional-options "-fPIC" { target fpic } } */
> +
> +extern int v[42], w;
> +void foo (void);
> +
> +asm ("# %cc0: %cc1:" :: ":" (foo), ":" (v), ":" (&w));
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
