ifcvt: Try re-using CC for conditional moves.
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
parent
e9ebb86799
commit
aa8cfe7859
117
gcc/ifcvt.cc
117
gcc/ifcvt.cc
@ -83,7 +83,7 @@ static rtx_insn *last_active_insn (basic_block, int);
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static rtx_insn *find_active_insn_before (basic_block, rtx_insn *);
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static rtx_insn *find_active_insn_after (basic_block, rtx_insn *);
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static basic_block block_fallthru (basic_block);
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static rtx cond_exec_get_condition (rtx_insn *);
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static rtx cond_exec_get_condition (rtx_insn *, bool);
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static rtx noce_get_condition (rtx_insn *, rtx_insn **, bool);
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static int noce_operand_ok (const_rtx);
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static void merge_if_block (ce_if_block *);
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@ -427,7 +427,7 @@ cond_exec_process_insns (ce_if_block *ce_info ATTRIBUTE_UNUSED,
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/* Return the condition for a jump. Do not do any special processing. */
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static rtx
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cond_exec_get_condition (rtx_insn *jump)
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cond_exec_get_condition (rtx_insn *jump, bool get_reversed = false)
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{
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rtx test_if, cond;
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@ -439,8 +439,10 @@ cond_exec_get_condition (rtx_insn *jump)
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/* If this branches to JUMP_LABEL when the condition is false,
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reverse the condition. */
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if (GET_CODE (XEXP (test_if, 2)) == LABEL_REF
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&& label_ref_label (XEXP (test_if, 2)) == JUMP_LABEL (jump))
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if (get_reversed
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|| (GET_CODE (XEXP (test_if, 2)) == LABEL_REF
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&& label_ref_label (XEXP (test_if, 2))
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== JUMP_LABEL (jump)))
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{
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enum rtx_code rev = reversed_comparison_code (cond, jump);
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if (rev == UNKNOWN)
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@ -3152,6 +3154,50 @@ bb_valid_for_noce_process_p (basic_block test_bb, rtx cond,
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return false;
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}
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/* Helper function to emit a cmov sequence encapsulated in
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start_sequence () and end_sequence (). If NEED_CMOV is true
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we call noce_emit_cmove to create a cmove sequence. Otherwise emit
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a simple move. If successful, store the first instruction of the
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sequence in TEMP_DEST and the sequence costs in SEQ_COST. */
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static rtx_insn*
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try_emit_cmove_seq (struct noce_if_info *if_info, rtx temp,
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rtx cond, rtx new_val, rtx old_val, bool need_cmov,
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unsigned *cost, rtx *temp_dest,
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rtx cc_cmp = NULL, rtx rev_cc_cmp = NULL)
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{
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rtx_insn *seq = NULL;
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*cost = 0;
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rtx x = XEXP (cond, 0);
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rtx y = XEXP (cond, 1);
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rtx_code cond_code = GET_CODE (cond);
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start_sequence ();
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if (need_cmov)
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*temp_dest = noce_emit_cmove (if_info, temp, cond_code,
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x, y, new_val, old_val, cc_cmp, rev_cc_cmp);
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else
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{
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*temp_dest = temp;
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if (if_info->then_else_reversed)
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noce_emit_move_insn (temp, old_val);
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else
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noce_emit_move_insn (temp, new_val);
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}
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if (*temp_dest != NULL_RTX)
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{
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seq = get_insns ();
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*cost = seq_cost (seq, if_info->speed_p);
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}
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end_sequence ();
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return seq;
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}
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/* We have something like:
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if (x > y)
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@ -3209,7 +3255,9 @@ noce_convert_multiple_sets (struct noce_if_info *if_info)
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rtx cond = noce_get_condition (jump, &cond_earliest, false);
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rtx x = XEXP (cond, 0);
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rtx y = XEXP (cond, 1);
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rtx_code cond_code = GET_CODE (cond);
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rtx cc_cmp = cond_exec_get_condition (jump);
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rtx rev_cc_cmp = cond_exec_get_condition (jump, /* get_reversed */ true);
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/* The true targets for a conditional move. */
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auto_vec<rtx> targets;
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@ -3323,31 +3371,51 @@ noce_convert_multiple_sets (struct noce_if_info *if_info)
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old_val = lowpart_subreg (dst_mode, old_val, src_mode);
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}
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rtx temp_dest = NULL_RTX;
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/* Try emitting a conditional move passing the backend the
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canonicalized comparison. The backend is then able to
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recognize expressions like
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if (need_cmov)
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if (x > y)
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y = x;
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as min/max and emit an insn, accordingly. */
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unsigned cost1 = 0, cost2 = 0;
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rtx_insn *seq, *seq1, *seq2;
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rtx temp_dest = NULL_RTX, temp_dest1 = NULL_RTX, temp_dest2 = NULL_RTX;
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seq1 = try_emit_cmove_seq (if_info, temp, cond,
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new_val, old_val, need_cmov,
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&cost1, &temp_dest1);
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/* Here, we try to pass the backend a non-canonicalized cc comparison
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as well. This allows the backend to emit a cmov directly without
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creating an additional compare for each. If successful, costing
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is easier and this sequence is usually preferred. */
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seq2 = try_emit_cmove_seq (if_info, target, cond,
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new_val, old_val, need_cmov,
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&cost2, &temp_dest2, cc_cmp, rev_cc_cmp);
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/* Check which version is less expensive. */
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if (seq1 != NULL_RTX && (cost1 <= cost2 || seq2 == NULL_RTX))
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{
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/* Actually emit the conditional move. */
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temp_dest = noce_emit_cmove (if_info, temp, cond_code,
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x, y, new_val, old_val);
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/* If we failed to expand the conditional move, drop out and don't
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try to continue. */
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if (temp_dest == NULL_RTX)
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{
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end_sequence ();
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return FALSE;
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}
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seq = seq1;
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temp_dest = temp_dest1;
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}
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else if (seq2 != NULL_RTX)
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{
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seq = seq2;
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temp_dest = temp_dest2;
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}
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else
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{
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if (if_info->then_else_reversed)
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noce_emit_move_insn (temp, old_val);
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else
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noce_emit_move_insn (temp, new_val);
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temp_dest = temp;
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/* Nothing worked, bail out. */
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end_sequence ();
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return FALSE;
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}
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/* End the sub sequence and emit to the main sequence. */
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emit_insn (seq);
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/* Bookkeeping. */
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count++;
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targets.safe_push (target);
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@ -3361,7 +3429,8 @@ noce_convert_multiple_sets (struct noce_if_info *if_info)
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/* Now fixup the assignments. */
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for (int i = 0; i < count; i++)
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noce_emit_move_insn (targets[i], temporaries[i]);
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if (targets[i] != temporaries[i])
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noce_emit_move_insn (targets[i], temporaries[i]);
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/* Actually emit the sequence if it isn't too expensive. */
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rtx_insn *seq = get_insns ();
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