Robin Dapp <rd...@linux.ibm.com> writes:
> noce_convert_multiple_sets creates temporaries for the destination of
> every emitted cmov and expects subsequent passes to get rid of them. This
> does not happen every time and even if the temporaries are removed, code
> generation can be affected adversely. In this patch, temporaries are
> only created if the destination of a set is used in an emitted condition
> check.
Still digesting the series, but a couple of implementation questions:
>
> ---
> gcc/ifcvt.c | 54 ++++++++++++++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 51 insertions(+), 3 deletions(-)
>
> diff --git a/gcc/ifcvt.c b/gcc/ifcvt.c
> index e95ff9ee9b0..253b8a96c1a 100644
> --- a/gcc/ifcvt.c
> +++ b/gcc/ifcvt.c
> @@ -99,6 +99,10 @@ static int dead_or_predicable (basic_block, basic_block,
> basic_block,
> edge, int);
> static void noce_emit_move_insn (rtx, rtx);
> static rtx_insn *block_has_only_trap (basic_block);
> +static void check_need_temps (basic_block bb,
> + hash_map<rtx, bool> *need_temp,
> + rtx cond);
> +
>
> /* Count the number of non-jump active insns in BB. */
>
> @@ -3145,6 +3149,12 @@ noce_convert_multiple_sets (struct noce_if_info
> *if_info)
> auto_vec<rtx_insn *> unmodified_insns;
> int count = 0;
>
> + hash_map<rtx, bool> need_temps;
> +
> + check_need_temps (then_bb, &need_temps, cond);
Is the separate need_temps scan required for correctness? It looked
like we could test:
if (reg_overlap_mentioned_p (dest, cond))
...
on-the-fly during the main noce_convert_multiple_sets loop.
> +
> + hash_map<rtx, bool> temps_created;
> +
> FOR_BB_INSNS (then_bb, insn)
> {
> /* Skip over non-insns. */
> @@ -3155,10 +3165,20 @@ noce_convert_multiple_sets (struct noce_if_info
> *if_info)
> gcc_checking_assert (set);
>
> rtx target = SET_DEST (set);
> - rtx temp = gen_reg_rtx (GET_MODE (target));
> rtx new_val = SET_SRC (set);
> rtx old_val = target;
>
> + rtx dest = SET_DEST (set);
> +
> + rtx temp;
> + if (need_temps.get (dest))
> + {
> + temp = gen_reg_rtx (GET_MODE (target));
> + temps_created.put (target, true);
> + }
> + else
> + temp = target;
> +
> /* If we were supposed to read from an earlier write in this block,
> we've changed the register allocation. Rewire the read. While
> we are looking, also try to catch a swap idiom. */
> @@ -3242,8 +3262,8 @@ noce_convert_multiple_sets (struct noce_if_info
> *if_info)
>
> /* Now fixup the assignments. */
> for (int i = 0; i < count; i++)
> - noce_emit_move_insn (targets[i], temporaries[i]);
> -
> + if (temps_created.get(targets[i]) && targets[i] != temporaries[i])
> + noce_emit_move_insn (targets[i], temporaries[i]);
Would it work to set temporaries[i] to targets[i] whenever a temporary
isn't needed, and avoid temps_created?
Thanks,
Richard
>
> /* Actually emit the sequence if it isn't too expensive. */
> rtx_insn *seq = get_insns ();
> @@ -3749,6 +3769,34 @@ check_cond_move_block (basic_block bb,
> return TRUE;
> }
>
> +/* Check for which sets we need to emit temporaries to hold the destination
> of
> + a conditional move. */
> +static void
> +check_need_temps (basic_block bb, hash_map<rtx, bool> *need_temp, rtx cond)
> +{
> + rtx_insn *insn;
> +
> + FOR_BB_INSNS (bb, insn)
> + {
> + rtx set, dest;
> +
> + if (!active_insn_p (insn))
> + continue;
> +
> + set = single_set (insn);
> + if (set == NULL_RTX)
> + continue;
> +
> + dest = SET_DEST (set);
> +
> + /* noce_emit_cmove will emit the condition check every time it is
> called
> + so we need a temp register if the destination is modified. */
> + if (reg_overlap_mentioned_p (dest, cond))
> + need_temp->put (dest, true);
> + }
> +}
> +
> +
> /* Given a basic block BB suitable for conditional move conversion,
> a condition COND, and pointer maps THEN_VALS and ELSE_VALS containing
> the register values depending on COND, emit the insns in the block as
