Re: -fuse-caller-save - Enable for MIPS

[Richard Sandiford <rdsandiford at googlemail dot com>]

Tom de Vries <Tom_deVries@mentor.com> writes:
> 2014-01-12  Radovan Obradovic  <robradovic@mips.com>
>             Tom de Vries  <tom@codesourcery.com>
>
> 	* config/mips/mips-protos.h (mips_emit_call_insn): Declare.
> 	* config/mips/mips.h (POST_CALL_TMP_REG): Define.
> 	* config/mips/mips.c (mips_emit_call_insn): Remove static.  Use
> 	last_call_insn.  Add POST_CALL_TMP_REG clobber
> 	 (mips_split_call): Use POST_CALL_TMP_REG.
> 	(TARGET_CALL_FUSAGE_CONTAINS_NON_CALLEE_CLOBBERS): Redefine to true.
> 	* config/mips/mips.md (define_expand "untyped_call"): Use
> 	mips_emit_call_insn.
>
> 	* gcc.target/mips/mips.exp: Add use-caller-save to -ffoo/-fno-foo
> 	options.
> 	* gcc.target/mips/fuse-caller-save.h: New include file.
> 	* gcc.target/mips/fuse-caller-save.c: New test.
> 	* gcc.target/mips/fuse-caller-save-mips16.c: Same.
> 	* gcc.target/mips/fuse-caller-save-micromips.c: Same.

Sorry, a couple of things, but this is looking pretty good:

>  mips_emit_call_insn (rtx pattern, rtx orig_addr, rtx addr, bool lazy_p)
>  {
>    rtx insn, reg;
>  
> -  insn = emit_call_insn (pattern);
> +  emit_call_insn (pattern);
> +  insn = last_call_insn ();
>  
>    if (TARGET_MIPS16 && mips_use_pic_fn_addr_reg_p (orig_addr))
>      {

This change isn't necessary; emit_call_insn is defined to return a CALL_INSN.

> @@ -2843,6 +2844,16 @@ mips_emit_call_insn (rtx pattern, rtx orig_addr, rtx addr, bool lazy_p)
>  	       gen_rtx_REG (Pmode, GOT_VERSION_REGNUM));
>        emit_insn (gen_update_got_version ());
>      }
> +
> +  if (TARGET_MIPS16
> +      && TARGET_EXPLICIT_RELOCS
> +      && TARGET_CALL_CLOBBERED_GP
> +      && !find_reg_note (insn, REG_NORETURN, 0))
> +    {
> +      rtx post_call_tmp_reg = gen_rtx_REG (word_mode, POST_CALL_TMP_REG);
> +      clobber_reg (&CALL_INSN_FUNCTION_USAGE (insn), post_call_tmp_reg);
> +    }

The REG_NORETURN note won't be around yet, so we might as well drop
that line.  I'm not sure how useful it would be anyway since values
are never live across a noreturn call.

> +/* Temporary register that is used after a call.  $4 and $5 are used for

Might as well make it "...used when restoring $gp after a call", now that
it's not as obvious from context.

> +   returning complex double values in soft-float code, so $6 is the first
> +   suitable candidate for !TARGET_MIPS16.  For TARGET_MIPS16, we use
> +   PIC_OFFSET_TABLE_REGNUM instead.  */

!TARGET_MIPS16 and TARGET_MIPS16 are the wrong way around:

   suitable candidate for TARGET_MIPS16.  For !TARGET_MIPS16 we can use
   $gp itself as the temporary.  */

> +/* The scan of the sp-relative saves will fail for -O0 and -O1.
> +   For -flto, scans will fail because there's no code in the .s file.  */
> +/* { dg-skip-if "" { *-*-* }  { "-O0" "-O1" "-flto"} } */

The -flto thing is handled automatically by the testsuite
(see force_conventional_output_for) so that one should be left out.

I'm a bit surprised that it doesn't work at -O1 for a simple test
like this though.  What goes wrong?

Thanks,
Richard