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fwprop: Allow (subreg (mem)) simplifications

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Suppose we have:

    (set (reg/v:TF 63) (mem/c:TF (reg/v:DI 62)))
    (set (reg:FPRX2 66) (subreg:FPRX2 (reg/v:TF 63) 0))

It is clearly profitable to propagate the first insn into the second
one and get:

    (set (reg:FPRX2 66) (mem/c:FPRX2 (reg/v:DI 62)))

fwprop actually manages to perform this, but doesn't think the result is
worth it, which results in unnecessary store/load sequences on s390.
Improve the situation by classifying SUBREG -> MEM changes as
profitable.

gcc/ChangeLog:

2021-01-15  Ilya Leoshkevich  <iii@linux.ibm.com>

	* fwprop.c (fwprop_propagation::classify_result): Allow
	(subreg (mem)) simplifications.
This commit is contained in:
Ilya Leoshkevich 2021-01-15 00:14:56 +01:00
parent f645da0e4a
commit efb6bc55a9
1 changed files with 28 additions and 5 deletions
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33
gcc/fwprop.c
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@ -176,7 +176,7 @@ namespace
static const uint16_t CONSTANT = FIRST_SPARE_RESULT << 1;
static const uint16_t PROFITABLE = FIRST_SPARE_RESULT << 2;
fwprop_propagation (rtx_insn *, rtx, rtx);
fwprop_propagation (insn_info *, insn_info *, rtx, rtx);
bool changed_mem_p () const { return result_flags & CHANGED_MEM; }
bool folded_to_constants_p () const;
@ -185,13 +185,20 @@ namespace
bool check_mem (int, rtx) final override;
void note_simplification (int, uint16_t, rtx, rtx) final override;
uint16_t classify_result (rtx, rtx);
private:
const bool single_use_p;
const bool single_ebb_p;
};
}
/* Prepare to replace FROM with TO in INSN. */
fwprop_propagation::fwprop_propagation (rtx_insn *insn, rtx from, rtx to)
: insn_propagation (insn, from, to)
fwprop_propagation::fwprop_propagation (insn_info *use_insn,
insn_info *def_insn, rtx from, rtx to)
: insn_propagation (use_insn->rtl (), from, to),
single_use_p (def_insn->num_uses () == 1),
single_ebb_p (use_insn->ebb () == def_insn->ebb ())
{
should_check_mems = true;
should_note_simplifications = true;
@ -262,6 +269,22 @@ fwprop_propagation::classify_result (rtx old_rtx, rtx new_rtx)
&& GET_MODE (new_rtx) == GET_MODE_INNER (GET_MODE (from)))
return PROFITABLE;
/* Allow (subreg (mem)) -> (mem) simplifications with the following
exceptions:
1) Propagating (mem)s into multiple uses is not profitable.
2) Propagating (mem)s across EBBs may not be profitable if the source EBB
runs less frequently.
3) Propagating (mem)s into paradoxical (subreg)s is not profitable.
4) Creating new (mem/v)s is not correct, since DCE will not remove the old
ones. */
if (single_use_p
&& single_ebb_p
&& SUBREG_P (old_rtx)
&& !paradoxical_subreg_p (old_rtx)
&& MEM_P (new_rtx)
&& !MEM_VOLATILE_P (new_rtx))
return PROFITABLE;
return 0;
}
@ -363,7 +386,7 @@ try_fwprop_subst_note (insn_info *use_insn, insn_info *def_insn,
rtx_insn *use_rtl = use_insn->rtl ();
insn_change_watermark watermark;
fwprop_propagation prop (use_rtl, dest, src);
fwprop_propagation prop (use_insn, def_insn, dest, src);
if (!prop.apply_to_rvalue (&XEXP (note, 0)))
{
if (dump_file && (dump_flags & TDF_DETAILS))
@ -426,7 +449,7 @@ try_fwprop_subst_pattern (obstack_watermark &attempt, insn_change &use_change,
rtx_insn *use_rtl = use_insn->rtl ();
insn_change_watermark watermark;
fwprop_propagation prop (use_rtl, dest, src);
fwprop_propagation prop (use_insn, def_insn, dest, src);
if (!prop.apply_to_pattern (loc))
{
if (dump_file && (dump_flags & TDF_DETAILS))