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ifcvt: Try re-using CC for conditional moves.

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Following up on the previous patch, this patch makes
noce_convert_multiple emit two cmov sequences:  The same one as before
and a second one that tries to re-use the existing CC.  Then their costs
are compared and the cheaper one is selected.

gcc/ChangeLog:

	* ifcvt.cc (cond_exec_get_condition): New parameter to allow getting the
	reversed comparison.
	(try_emit_cmove_seq): New function to facilitate creating a cmov
	sequence.
	(noce_convert_multiple_sets): Create two sequences and use the less
	expensive one.
This commit is contained in:
Robin Dapp 2022-01-19 17:36:36 +01:00
parent e9ebb86799
commit aa8cfe7859
1 changed files with 93 additions and 24 deletions
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115
gcc/ifcvt.cc
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@ -83,7 +83,7 @@ static rtx_insn *last_active_insn (basic_block, int);
static rtx_insn *find_active_insn_before (basic_block, rtx_insn *);
static rtx_insn *find_active_insn_after (basic_block, rtx_insn *);
static basic_block block_fallthru (basic_block);
static rtx cond_exec_get_condition (rtx_insn *);
static rtx cond_exec_get_condition (rtx_insn *, bool);
static rtx noce_get_condition (rtx_insn *, rtx_insn **, bool);
static int noce_operand_ok (const_rtx);
static void merge_if_block (ce_if_block *);
@ -427,7 +427,7 @@ cond_exec_process_insns (ce_if_block *ce_info ATTRIBUTE_UNUSED,
/* Return the condition for a jump. Do not do any special processing. */
static rtx
cond_exec_get_condition (rtx_insn *jump)
cond_exec_get_condition (rtx_insn *jump, bool get_reversed = false)
{
rtx test_if, cond;
@ -439,8 +439,10 @@ cond_exec_get_condition (rtx_insn *jump)
/* If this branches to JUMP_LABEL when the condition is false,
reverse the condition. */
if (GET_CODE (XEXP (test_if, 2)) == LABEL_REF
&& label_ref_label (XEXP (test_if, 2)) == JUMP_LABEL (jump))
if (get_reversed
|| (GET_CODE (XEXP (test_if, 2)) == LABEL_REF
&& label_ref_label (XEXP (test_if, 2))
== JUMP_LABEL (jump)))
{
enum rtx_code rev = reversed_comparison_code (cond, jump);
if (rev == UNKNOWN)
@ -3152,6 +3154,50 @@ bb_valid_for_noce_process_p (basic_block test_bb, rtx cond,
return false;
}
/* Helper function to emit a cmov sequence encapsulated in
start_sequence () and end_sequence (). If NEED_CMOV is true
we call noce_emit_cmove to create a cmove sequence. Otherwise emit
a simple move. If successful, store the first instruction of the
sequence in TEMP_DEST and the sequence costs in SEQ_COST. */
static rtx_insn*
try_emit_cmove_seq (struct noce_if_info *if_info, rtx temp,
rtx cond, rtx new_val, rtx old_val, bool need_cmov,
unsigned *cost, rtx *temp_dest,
rtx cc_cmp = NULL, rtx rev_cc_cmp = NULL)
{
rtx_insn *seq = NULL;
*cost = 0;
rtx x = XEXP (cond, 0);
rtx y = XEXP (cond, 1);
rtx_code cond_code = GET_CODE (cond);
start_sequence ();
if (need_cmov)
*temp_dest = noce_emit_cmove (if_info, temp, cond_code,
x, y, new_val, old_val, cc_cmp, rev_cc_cmp);
else
{
*temp_dest = temp;
if (if_info->then_else_reversed)
noce_emit_move_insn (temp, old_val);
else
noce_emit_move_insn (temp, new_val);
}
if (*temp_dest != NULL_RTX)
{
seq = get_insns ();
*cost = seq_cost (seq, if_info->speed_p);
}
end_sequence ();
return seq;
}
/* We have something like:
if (x > y)
@ -3209,7 +3255,9 @@ noce_convert_multiple_sets (struct noce_if_info *if_info)
rtx cond = noce_get_condition (jump, &cond_earliest, false);
rtx x = XEXP (cond, 0);
rtx y = XEXP (cond, 1);
rtx_code cond_code = GET_CODE (cond);
rtx cc_cmp = cond_exec_get_condition (jump);
rtx rev_cc_cmp = cond_exec_get_condition (jump, /* get_reversed */ true);
/* The true targets for a conditional move. */
auto_vec<rtx> targets;
@ -3323,30 +3371,50 @@ noce_convert_multiple_sets (struct noce_if_info *if_info)
old_val = lowpart_subreg (dst_mode, old_val, src_mode);
}
rtx temp_dest = NULL_RTX;
/* Try emitting a conditional move passing the backend the
canonicalized comparison. The backend is then able to
recognize expressions like
if (need_cmov)
{
/* Actually emit the conditional move. */
temp_dest = noce_emit_cmove (if_info, temp, cond_code,
x, y, new_val, old_val);
if (x > y)
y = x;
/* If we failed to expand the conditional move, drop out and don't
try to continue. */
if (temp_dest == NULL_RTX)
as min/max and emit an insn, accordingly. */
unsigned cost1 = 0, cost2 = 0;
rtx_insn *seq, *seq1, *seq2;
rtx temp_dest = NULL_RTX, temp_dest1 = NULL_RTX, temp_dest2 = NULL_RTX;
seq1 = try_emit_cmove_seq (if_info, temp, cond,
new_val, old_val, need_cmov,
&cost1, &temp_dest1);
/* Here, we try to pass the backend a non-canonicalized cc comparison
as well. This allows the backend to emit a cmov directly without
creating an additional compare for each. If successful, costing
is easier and this sequence is usually preferred. */
seq2 = try_emit_cmove_seq (if_info, target, cond,
new_val, old_val, need_cmov,
&cost2, &temp_dest2, cc_cmp, rev_cc_cmp);
/* Check which version is less expensive. */
if (seq1 != NULL_RTX && (cost1 <= cost2 || seq2 == NULL_RTX))
{
seq = seq1;
temp_dest = temp_dest1;
}
else if (seq2 != NULL_RTX)
{
seq = seq2;
temp_dest = temp_dest2;
}
else
{
/* Nothing worked, bail out. */
end_sequence ();
return FALSE;
}
}
else
{
if (if_info->then_else_reversed)
noce_emit_move_insn (temp, old_val);
else
noce_emit_move_insn (temp, new_val);
temp_dest = temp;
}
/* End the sub sequence and emit to the main sequence. */
emit_insn (seq);
/* Bookkeeping. */
count++;
@ -3361,6 +3429,7 @@ noce_convert_multiple_sets (struct noce_if_info *if_info)
/* Now fixup the assignments. */
for (int i = 0; i < count; i++)
if (targets[i] != temporaries[i])
noce_emit_move_insn (targets[i], temporaries[i]);
/* Actually emit the sequence if it isn't too expensive. */