On Wed, Sep 19, 2012 at 3:51 AM, Joern Rennecke <amyl...@spamcop.net> wrote:
> I am about to submit the ARCompact target port; this port needs a few
> patches to target-independent code.
>
> There is a move pattern with 20 alternatives; a few of them need a simple
> function call to decide which output pattern to use. With the '@'-syntax
> for multi-alternative templates, each alternative is still a one-liner.
> Requiring to transform this into some switch statement would make the thing
> several times as big, and very hard to take in; besides, it is generally
> a maintenance issue if you have to completely rewrite a multi-alternative
> template if you just change one alternative from a constant to some C-code,
> or vice versa for the last non-literal alternative.
>
> The attached patch makes the '*' syntax for C code fragments available for
> individual alternatives of an '@' multi-alternative output template.
> It does this by translating the input into a switch statement in the
> generated file, so in a way this is just syntactic sugar, but it's syntactic
> sugar that makes some machine descriptions easier to write and change.
>
> Bootstrapped in revision 191429 for i686-pc-linux-gnu.
>
> I've been wondering if it'd make sense to also support for '{' / '}' ,
> but at least in the ARCompact context, I think the use of that syntax
> inside a multi-alternative template would reduce rather than improve
> legibility, so, having no application for the '{' / '}' in that place,
> there seems to be no use in adding support for that at this point in time.
I think that needs to be documented somewhere in the internals manual,
possibly with an example.
Richard.
> 2008-11-19 J"orn Rennecke <joern.renne...@arc.com>
>
> * genoutput.c (process_template): Process '*' in '@' alternatives.
>
> Index: genoutput.c
> ===================================================================
> --- genoutput.c (revision 191429)
> +++ genoutput.c (working copy)
> @@ -662,19 +662,55 @@ process_template (struct data *d, const
> list of assembler code templates, one for each alternative. */
> else if (template_code[0] == '@')
> {
> - d->template_code = 0;
> - d->output_format = INSN_OUTPUT_FORMAT_MULTI;
> + int found_star = 0;
>
> - printf ("\nstatic const char * const output_%d[] = {\n",
> d->code_number);
> + for (cp = &template_code[1]; *cp; )
> + {
> + while (ISSPACE (*cp))
> + cp++;
> + if (*cp == '*')
> + found_star = 1;
> + while (!IS_VSPACE (*cp) && *cp != '\0')
> + ++cp;
> + }
> + d->template_code = 0;
> + if (found_star)
> + {
> + d->output_format = INSN_OUTPUT_FORMAT_FUNCTION;
> + puts ("\nstatic const char *");
> + printf ("output_%d (rtx *operands ATTRIBUTE_UNUSED, "
> + "rtx insn ATTRIBUTE_UNUSED)\n", d->code_number);
> + puts ("{");
> + puts (" switch (which_alternative)\n {");
> + }
> + else
> + {
> + d->output_format = INSN_OUTPUT_FORMAT_MULTI;
> + printf ("\nstatic const char * const output_%d[] = {\n",
> + d->code_number);
> + }
>
> for (i = 0, cp = &template_code[1]; *cp; )
> {
> - const char *ep, *sp;
> + const char *ep, *sp, *bp;
>
> while (ISSPACE (*cp))
> cp++;
>
> - printf (" \"");
> + bp = cp;
> + if (found_star)
> + {
> + printf (" case %d:", i);
> + if (*cp == '*')
> + {
> + printf ("\n ");
> + cp++;
> + }
> + else
> + printf (" return \"");
> + }
> + else
> + printf (" \"");
>
> for (ep = sp = cp; !IS_VSPACE (*ep) && *ep != '\0'; ++ep)
> if (!ISSPACE (*ep))
> @@ -690,7 +726,18 @@ process_template (struct data *d, const
> cp++;
> }
>
> - printf ("\",\n");
> + if (!found_star)
> + puts ("\",");
> + else if (*bp != '*')
> + puts ("\";");
> + else
> + {
> + /* The usual action will end with a return.
> + If there is neither break or return at the end, this is
> + assumed to be intentional; this allows to have multiple
> + consecutive alternatives share some code. */
> + puts ("");
> + }
> i++;
> }
> if (i == 1)
> @@ -700,7 +747,10 @@ process_template (struct data *d, const
> error_with_line (d->lineno,
> "wrong number of alternatives in the output
> template");
>
> - printf ("};\n");
> + if (found_star)
> + puts (" default: gcc_unreachable ();\n }\n}");
> + else
> + printf ("};\n");
> }
> else
> {
>
