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Re: optimization/1945 fix
- To: Richard Henderson <rth at redhat dot com>
- Subject: Re: optimization/1945 fix
- From: Shane Nay <shane at agendacomputing dot com>
- Date: Fri, 16 Feb 2001 04:47:39 -0800
- Cc: gcc-patches at gcc dot gnu dot org
- Organization: Agenda Computing
- References: <email@example.com> <20010215205711.C18831@redhat.com>
- Reply-To: shane at agendacomputing dot com
On Thursday 15 February 2001 20:57, Richard Henderson wrote:
> On Thu, Feb 15, 2001 at 05:07:19AM -0800, Shane Nay wrote:
> > + /* We need to check to make sure that we should be
> > + emitting shift code, because if the argument isn't
> > + getting used, it is considered a bug to emit
> > + preparation code for it in mips_expand_prologue.
> > + */
> Ug. I don't think you want to be scanning the entire function.
> I'd have said check "BASIC_BLOCK (0)->global_live_at_start", but
> just remembered that that isn't valid at this point.
Really I think it's right to have this evaluation of whether or not registers
are needed in the flow_analysis because it benefits more than one platform.
Maybe instead of REG_MAYBE_DEAD, we should have REG_DONT_KILL, and assume all
manipulations are worthy of dumping if they aren't used unless the
architecture specific piece notes them as REG_DONT_KILL.
> As much as I dislike the thing, I think you'll have to add a
> REG_MAYBE_UNUSED note to these shift instructions.
2001-02-16 Shane Nay <firstname.lastname@example.org>
* mips.c (mips_expand_prologue) Add REG_MAYBE_DEAD
notes to structs passed by value since we don't know at that
point whether or not we'll need the value.
RCS file: /cvs/gcc/gcc/gcc/config/mips/mips.c,v
retrieving revision 1.107
diff -u -3 -r1.107 mips.c
--- mips.c 2001/02/05 16:34:40 1.107
+++ mips.c 2001/02/16 13:43:34
@@ -7115,13 +7115,21 @@
for (i = 0; i < num; i++)
+ rtx insn;
rtx pattern = RTVEC_ELT (adjust, i);
if (GET_CODE (pattern) != SET
|| GET_CODE (SET_SRC (pattern)) != ASHIFT)
abort_with_insn (pattern, "Insn is not a shift");
PUT_CODE (SET_SRC (pattern), ASHIFTRT);
- emit_insn (pattern);
+ insn=emit_insn (pattern);
+ /* Since we are emitting these shift instructions without
+ checking whether they are necessary, we must note
+ that they might be dead. */
+ REG_NOTES(insn) = gen_rtx_EXPR_LIST (REG_MAYBE_DEAD, NULL_RTX,
+ REG_NOTES (insn));