[PATCH v2] ifcvt: Handle multiple rewired regs and refactor noce_convert_multiple_sets

Manolis Tsamis manolis.tsamis@vrull.eu
Tue Nov 21 18:00:54 GMT 2023


The existing implementation of need_cmov_or_rewire and
noce_convert_multiple_sets_1 assumes that sets are either REG or SUBREG.
This commit enchances them so they can handle/rewire arbitrary set statements.

To do that a new helper struct noce_multiple_sets_info is introduced which is
used by noce_convert_multiple_sets and its helper functions. This results in
cleaner function signatures, improved efficientcy (a number of vecs and hash
set/map are replaced with a single vec of struct) and simplicity.

gcc/ChangeLog:

	* ifcvt.cc (need_cmov_or_rewire): Renamed init_noce_multiple_sets_info.
	(init_noce_multiple_sets_info): Initialize noce_multiple_sets_info.
	(noce_convert_multiple_sets_1): Use noce_multiple_sets_info and handle
	rewiring of multiple registers.
	(noce_convert_multiple_sets): Updated to use noce_multiple_sets_info.
	* ifcvt.h (struct noce_multiple_sets_info): Introduce new struct
	noce_multiple_sets_info to store info for noce_convert_multiple_sets.

Signed-off-by: Manolis Tsamis <manolis.tsamis@vrull.eu>
---

Changes in v2:
        - Made standalone patch.
        - Better comments, some more checks.

 gcc/ifcvt.cc | 252 +++++++++++++++++++++++----------------------------
 gcc/ifcvt.h  |  16 ++++
 2 files changed, 129 insertions(+), 139 deletions(-)

diff --git a/gcc/ifcvt.cc b/gcc/ifcvt.cc
index a0af553b9ff..9486d54de34 100644
--- a/gcc/ifcvt.cc
+++ b/gcc/ifcvt.cc
@@ -98,14 +98,10 @@ static bool dead_or_predicable (basic_block, basic_block, basic_block,
 				edge, bool);
 static void noce_emit_move_insn (rtx, rtx);
 static rtx_insn *block_has_only_trap (basic_block);
-static void need_cmov_or_rewire (basic_block, hash_set<rtx_insn *> *,
-				 hash_map<rtx_insn *, int> *);
+static void init_noce_multiple_sets_info (basic_block,
+  auto_delete_vec<noce_multiple_sets_info> &);
 static bool noce_convert_multiple_sets_1 (struct noce_if_info *,
-					  hash_set<rtx_insn *> *,
-					  hash_map<rtx_insn *, int> *,
-					  auto_vec<rtx> *,
-					  auto_vec<rtx> *,
-					  auto_vec<rtx_insn *> *, int *);
+  auto_delete_vec<noce_multiple_sets_info> &, int *);
 
 /* Count the number of non-jump active insns in BB.  */
 
@@ -3270,24 +3266,13 @@ noce_convert_multiple_sets (struct noce_if_info *if_info)
   rtx x = XEXP (cond, 0);
   rtx y = XEXP (cond, 1);
 
-  /* The true targets for a conditional move.  */
-  auto_vec<rtx> targets;
-  /* The temporaries introduced to allow us to not consider register
-     overlap.  */
-  auto_vec<rtx> temporaries;
-  /* The insns we've emitted.  */
-  auto_vec<rtx_insn *> unmodified_insns;
-
-  hash_set<rtx_insn *> need_no_cmov;
-  hash_map<rtx_insn *, int> rewired_src;
-
-  need_cmov_or_rewire (then_bb, &need_no_cmov, &rewired_src);
+  auto_delete_vec<noce_multiple_sets_info> insn_info;
+  init_noce_multiple_sets_info (then_bb, insn_info);
 
   int last_needs_comparison = -1;
 
   bool ok = noce_convert_multiple_sets_1
-    (if_info, &need_no_cmov, &rewired_src, &targets, &temporaries,
-     &unmodified_insns, &last_needs_comparison);
+    (if_info, insn_info, &last_needs_comparison);
   if (!ok)
       return false;
 
@@ -3302,8 +3287,7 @@ noce_convert_multiple_sets (struct noce_if_info *if_info)
       end_sequence ();
       start_sequence ();
       ok = noce_convert_multiple_sets_1
-	(if_info, &need_no_cmov, &rewired_src, &targets, &temporaries,
-	 &unmodified_insns, &last_needs_comparison);
+	(if_info, insn_info, &last_needs_comparison);
       /* Actually we should not fail anymore if we reached here,
 	 but better still check.  */
       if (!ok)
@@ -3312,12 +3296,12 @@ noce_convert_multiple_sets (struct noce_if_info *if_info)
 
   /* We must have seen some sort of insn to insert, otherwise we were
      given an empty BB to convert, and we can't handle that.  */
-  gcc_assert (!unmodified_insns.is_empty ());
+  gcc_assert (!insn_info.is_empty ());
 
   /* Now fixup the assignments.  */
-  for (unsigned i = 0; i < targets.length (); i++)
-    if (targets[i] != temporaries[i])
-      noce_emit_move_insn (targets[i], temporaries[i]);
+  for (unsigned i = 0; i < insn_info.length (); i++)
+    if (insn_info[i]->target != insn_info[i]->temporary)
+      noce_emit_move_insn (insn_info[i]->target, insn_info[i]->temporary);
 
   /* Actually emit the sequence if it isn't too expensive.  */
   rtx_insn *seq = get_insns ();
@@ -3332,10 +3316,10 @@ noce_convert_multiple_sets (struct noce_if_info *if_info)
     set_used_flags (insn);
 
   /* Mark all our temporaries and targets as used.  */
-  for (unsigned i = 0; i < targets.length (); i++)
+  for (unsigned i = 0; i < insn_info.length (); i++)
     {
-      set_used_flags (temporaries[i]);
-      set_used_flags (targets[i]);
+      set_used_flags (insn_info[i]->temporary);
+      set_used_flags (insn_info[i]->target);
     }
 
   set_used_flags (cond);
@@ -3354,7 +3338,7 @@ noce_convert_multiple_sets (struct noce_if_info *if_info)
       return false;
 
   emit_insn_before_setloc (seq, if_info->jump,
-			   INSN_LOCATION (unmodified_insns.last ()));
+			   INSN_LOCATION (insn_info.last ()->unmodified_insn));
 
   /* Clean up THEN_BB and the edges in and out of it.  */
   remove_edge (find_edge (test_bb, join_bb));
@@ -3389,21 +3373,13 @@ check_for_cc_cmp_clobbers (rtx dest, const_rtx, void *p0)
     p[0] = NULL_RTX;
 }
 
-/* This goes through all relevant insns of IF_INFO->then_bb and tries to
-   create conditional moves.  In case a simple move sufficis the insn
-   should be listed in NEED_NO_CMOV.  The rewired-src cases should be
-   specified via REWIRED_SRC.  TARGETS, TEMPORARIES and UNMODIFIED_INSNS
-   are specified and used in noce_convert_multiple_sets and should be passed
-   to this function..  */
+/* This goes through all relevant insns of IF_INFO->then_bb and tries to create
+   conditional moves.  Information for the insns is kept in INSN_INFO.  */
 
 static bool
 noce_convert_multiple_sets_1 (struct noce_if_info *if_info,
-			      hash_set<rtx_insn *> *need_no_cmov,
-			      hash_map<rtx_insn *, int> *rewired_src,
-			      auto_vec<rtx> *targets,
-			      auto_vec<rtx> *temporaries,
-			      auto_vec<rtx_insn *> *unmodified_insns,
-			      int *last_needs_comparison)
+			auto_delete_vec<noce_multiple_sets_info> &insn_info,
+			int *last_needs_comparison)
 {
   basic_block then_bb = if_info->then_bb;
   rtx_insn *jump = if_info->jump;
@@ -3421,11 +3397,6 @@ noce_convert_multiple_sets_1 (struct noce_if_info *if_info,
 
   rtx_insn *insn;
   int count = 0;
-
-  targets->truncate (0);
-  temporaries->truncate (0);
-  unmodified_insns->truncate (0);
-
   bool second_try = *last_needs_comparison != -1;
 
   FOR_BB_INSNS (then_bb, insn)
@@ -3434,6 +3405,8 @@ noce_convert_multiple_sets_1 (struct noce_if_info *if_info,
       if (!active_insn_p (insn))
 	continue;
 
+      noce_multiple_sets_info *info = insn_info[count];
+
       rtx set = single_set (insn);
       gcc_checking_assert (set);
 
@@ -3441,9 +3414,12 @@ noce_convert_multiple_sets_1 (struct noce_if_info *if_info,
       rtx temp;
 
       rtx new_val = SET_SRC (set);
-      if (int *ii = rewired_src->get (insn))
-	new_val = simplify_replace_rtx (new_val, (*targets)[*ii],
-					(*temporaries)[*ii]);
+
+      int i, ii;
+      FOR_EACH_VEC_ELT (info->rewired_src, i, ii)
+	new_val = simplify_replace_rtx (new_val, insn_info[ii]->target,
+					insn_info[ii]->temporary);
+
       rtx old_val = target;
 
       /* As we are transforming
@@ -3484,7 +3460,7 @@ noce_convert_multiple_sets_1 (struct noce_if_info *if_info,
       /* We have identified swap-style idioms before.  A normal
 	 set will need to be a cmov while the first instruction of a swap-style
 	 idiom can be a regular move.  This helps with costing.  */
-      bool need_cmov = !need_no_cmov->contains (insn);
+      bool need_cmov = info->need_cmov;
 
       /* If we had a non-canonical conditional jump (i.e. one where
 	 the fallthrough is to the "else" case) we need to reverse
@@ -3632,21 +3608,102 @@ noce_convert_multiple_sets_1 (struct noce_if_info *if_info,
 
       /* Bookkeeping.  */
       count++;
-      targets->safe_push (target);
-      temporaries->safe_push (temp_dest);
-      unmodified_insns->safe_push (insn);
+
+      info->target = target;
+      info->temporary = temp_dest;
+      info->unmodified_insn = insn;
     }
 
+  /* The number of processed insns must match init_noce_multiple_sets_info.  */
+  gcc_assert (count == (int) insn_info.length ());
+
   /* Even if we did not actually need the comparison, we want to make sure
      to try a second time in order to get rid of the temporaries.  */
   if (*last_needs_comparison == -1)
     *last_needs_comparison = 0;
 
-
   return true;
 }
 
+/* Find local swap-style idioms in BB and mark the first insn (1)
+   that is only a temporary as not needing a conditional move as
+   it is going to be dead afterwards anyway.
+
+     (1) int tmp = a;
+	 a = b;
+	 b = tmp;
+
+	 ifcvt
+	 -->
+
+	 tmp = a;
+	 a = cond ? b : a_old;
+	 b = cond ? tmp : b_old;
+
+    Additionally, store the index of insns like (2) when a subsequent
+    SET reads from their destination.
 
+    (2) int c = a;
+	int d = c;
+
+	ifcvt
+	-->
+
+	c = cond ? a : c_old;
+	d = cond ? d : c;     // Need to use c rather than c_old here.
+*/
+
+static void
+init_noce_multiple_sets_info (basic_block bb,
+		     auto_delete_vec<noce_multiple_sets_info> &insn_info)
+{
+  rtx_insn *insn;
+  int count = 0;
+  auto_vec<rtx> dests;
+
+  /* Iterate over all SETs, storing the destinations
+     in DEST.
+     - If we hit a SET that reads from a destination
+       that we have seen before and the corresponding register
+       is dead afterwards, the register does not need to be
+       moved conditionally.
+     - If we encounter a previously changed register,
+       rewire the read to the original source.  */
+  FOR_BB_INSNS (bb, insn)
+    {
+      if (!active_insn_p (insn))
+	continue;
+
+      noce_multiple_sets_info *info = new noce_multiple_sets_info;
+      info->target = NULL_RTX;
+      info->temporary = NULL_RTX;
+      info->unmodified_insn = NULL;
+      info->need_cmov = true;
+      insn_info.safe_push (info);
+
+      rtx set = single_set (insn);
+      gcc_checking_assert (set);
+
+      rtx src = SET_SRC (set);
+      rtx dest = SET_DEST (set);
+
+      /* Check if the current SET's source is the same
+	 as any previously seen destination.
+	 This is quadratic but the number of insns in BB
+	 is bounded by PARAM_MAX_RTL_IF_CONVERSION_INSNS.  */
+      for (int i = count - 1; i >= 0; --i)
+	if (reg_mentioned_p (dests[i], src))
+	  {
+	    if (find_reg_note (insn, REG_DEAD, src) != NULL_RTX)
+	      insn_info[i]->need_cmov = false;
+	    else
+	      insn_info[count]->rewired_src.safe_push (i);
+	  }
+
+      dests.safe_push (dest);
+      count++;
+    }
+}
 
 /* Return true iff basic block TEST_BB is comprised of only
    (SET (REG) (REG)) insns suitable for conversion to a series
@@ -4121,89 +4178,6 @@ check_cond_move_block (basic_block bb,
   return true;
 }
 
-/* Find local swap-style idioms in BB and mark the first insn (1)
-   that is only a temporary as not needing a conditional move as
-   it is going to be dead afterwards anyway.
-
-     (1) int tmp = a;
-	 a = b;
-	 b = tmp;
-
-	 ifcvt
-	 -->
-
-	 tmp = a;
-	 a = cond ? b : a_old;
-	 b = cond ? tmp : b_old;
-
-    Additionally, store the index of insns like (2) when a subsequent
-    SET reads from their destination.
-
-    (2) int c = a;
-	int d = c;
-
-	ifcvt
-	-->
-
-	c = cond ? a : c_old;
-	d = cond ? d : c;     // Need to use c rather than c_old here.
-*/
-
-static void
-need_cmov_or_rewire (basic_block bb,
-		     hash_set<rtx_insn *> *need_no_cmov,
-		     hash_map<rtx_insn *, int> *rewired_src)
-{
-  rtx_insn *insn;
-  int count = 0;
-  auto_vec<rtx_insn *> insns;
-  auto_vec<rtx> dests;
-
-  /* Iterate over all SETs, storing the destinations
-     in DEST.
-     - If we hit a SET that reads from a destination
-       that we have seen before and the corresponding register
-       is dead afterwards, the register does not need to be
-       moved conditionally.
-     - If we encounter a previously changed register,
-       rewire the read to the original source.  */
-  FOR_BB_INSNS (bb, insn)
-    {
-      rtx set, src, dest;
-
-      if (!active_insn_p (insn))
-	continue;
-
-      set = single_set (insn);
-      if (set == NULL_RTX)
-	continue;
-
-      src = SET_SRC (set);
-      if (SUBREG_P (src))
-	src = SUBREG_REG (src);
-      dest = SET_DEST (set);
-
-      /* Check if the current SET's source is the same
-	 as any previously seen destination.
-	 This is quadratic but the number of insns in BB
-	 is bounded by PARAM_MAX_RTL_IF_CONVERSION_INSNS.  */
-      if (REG_P (src))
-	for (int i = count - 1; i >= 0; --i)
-	  if (reg_overlap_mentioned_p (src, dests[i]))
-	    {
-	      if (find_reg_note (insn, REG_DEAD, src) != NULL_RTX)
-		need_no_cmov->add (insns[i]);
-	      else
-		rewired_src->put (insn, i);
-	    }
-
-      insns.safe_push (insn);
-      dests.safe_push (dest);
-
-      count++;
-    }
-}
-
 /* 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
diff --git a/gcc/ifcvt.h b/gcc/ifcvt.h
index be1385aabe4..83420fe1207 100644
--- a/gcc/ifcvt.h
+++ b/gcc/ifcvt.h
@@ -40,6 +40,22 @@ struct ce_if_block
   int pass;				/* Pass number.  */
 };
 
+struct noce_multiple_sets_info
+{
+  /* A list of indices to instructions that we need to rewire into this
+     instruction when we replace them with temporary conditional moves.  */
+  auto_vec<int> rewired_src;
+  /* The true targets for a conditional move.  */
+  rtx target;
+  /* The temporary introduced for this conditional move.  */
+  rtx temporary;
+  /* The original instruction that we're replacing.  */
+  rtx_insn *unmodified_insn;
+  /* True if a conditional move is needed.
+     False if a simple move can be used instead.  */
+  bool need_cmov;
+};
+
 /* Used by noce_process_if_block to communicate with its subroutines.
 
    The subroutines know that A and B may be evaluated freely.  They
-- 
2.34.1



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