[PR115042, LRA]: Postpone processing of new reload insns

LRA in this PR can not find regs for asm insn which requires 11
general regs when 13 regs are available.  Arm subtarget (thumb) has
two stores with low and high general regs.  LRA systematically chooses
stores involving low regs as having less costs and there are only 8
low regs.  That is because LRA (and reload) chooses (mov) insn
alternatives independently from register pressure.

The proposed patch postpones processing new reload insns until reload
pseudos are assigned and after that considers new reload insns.
Depending on the assignment LRA chooses insns involving low or high
regs.  Generally speaking it can change code generation in better or
worse way but it should be a rare case.

The patch does not contain the test as original test is too big (300KB
of C code).  Unfortunately cvise after 2 days of work managed to
decrease the test only to 100KB file.

gcc/ChangeLog:

	PR target/115042
	* lra-int.h (lra_constraint_insn_stack_clear): New prototype.
	* lra.cc (lra_constraint_insn_stack2): New vector.
	(lra_constraint_insn_stack_clear): New function.
	(lra): Initialize/finalize lra_constraint_insn_stack2.
	* lra-constraints.cc (lra_constraints): Use
	lra_constraint_insn_stack_clear to postpone processing new reload
	insns.

diff --git a/gcc/lra-constraints.cc b/gcc/lra-constraints.cc
index 1b5a875f7248d611ef114b1a26a75d123670edc9..1e1b0c4d1d872cd09c0c53a34972ca07ab5cbdcc 100644 (file)
--- a/gcc/lra-constraints.cc
+++ b/gcc/lra-constraints.cc
@@ -5514,10 +5514,9 @@ bool
 lra_constraints (bool first_p)
 {
   bool changed_p;
-  int i, hard_regno, new_insns_num;
-  unsigned int min_len, new_min_len, uid;
+  int i, hard_regno;
+  unsigned int uid;
   rtx set, x, reg, nosubreg_dest;
-  rtx_insn *original_insn;
   basic_block last_bb;
   bitmap_iterator bi;
 
@@ -5627,36 +5626,18 @@ lra_constraints (bool first_p)
      substituted by their equivalences.  */
   EXECUTE_IF_SET_IN_BITMAP (equiv_insn_bitmap, 0, uid, bi)
     lra_push_insn_by_uid (uid);
-  min_len = lra_insn_stack_length ();
-  new_insns_num = 0;
   last_bb = NULL;
   changed_p = false;
-  original_insn = NULL;
-  while ((new_min_len = lra_insn_stack_length ()) != 0)
+  auto constraint_insns = lra_constraint_insn_stack_clear ();
+  while (constraint_insns.length () != 0)
     {
-      curr_insn = lra_pop_insn ();
-      --new_min_len;
+      curr_insn = constraint_insns.pop ();
       curr_bb = BLOCK_FOR_INSN (curr_insn);
       if (curr_bb != last_bb)
        {
          last_bb = curr_bb;
          bb_reload_num = lra_curr_reload_num;
        }
-      if (min_len > new_min_len)
-       {
-         min_len = new_min_len;
-         new_insns_num = 0;
-         original_insn = curr_insn;
-       }
-      else if (combine_reload_insn (curr_insn, original_insn))
-       {
-         continue;
-        }
-      if (new_insns_num > MAX_RELOAD_INSNS_NUMBER)
-       internal_error
-         ("maximum number of generated reload insns per insn achieved (%d)",
-          MAX_RELOAD_INSNS_NUMBER);
-      new_insns_num++;
       if (DEBUG_INSN_P (curr_insn))
        {
          /* We need to check equivalence in debug insn and change
@@ -5747,7 +5728,15 @@ lra_constraints (bool first_p)
          init_curr_insn_input_reloads ();
          init_curr_operand_mode ();
          if (curr_insn_transform (false))
-           changed_p = true;
+           {
+             if (lra_insn_stack_length () != 0)
+               {
+                 auto reload_insn = lra_pop_insn ();
+                 if (!combine_reload_insn (reload_insn, curr_insn))
+                   lra_push_insn (reload_insn);
+               }
+             changed_p = true;
+           }
          /* Check non-transformed insns too for equiv change as USE
             or CLOBBER don't need reloads but can contain pseudos
             being changed on their equivalences.  */

diff --git a/gcc/lra-int.h b/gcc/lra-int.h
index 1c0561f496cfbc2f2aa5fd7df7c892f87a942ed5..18c4cf6eaeb0c065769bd5c3edca4fda4199920b 100644 (file)
--- a/gcc/lra-int.h
+++ b/gcc/lra-int.h
@@ -310,6 +310,7 @@ extern void lra_push_insn_by_uid (unsigned int);
 extern void lra_push_insn_and_update_insn_regno_info (rtx_insn *);
 extern rtx_insn *lra_pop_insn (void);
 extern unsigned int lra_insn_stack_length (void);
+extern vec<rtx_insn *> lra_constraint_insn_stack_clear (void);
 
 extern rtx lra_create_new_reg (machine_mode, rtx, enum reg_class, HARD_REG_SET *,
                               const char *);

diff --git a/gcc/lra.cc b/gcc/lra.cc
index 20a3db45747682d464905a7c266259095662216b..b4471a3e1c8e58d61ea2365a34ca434e1ef44901 100644 (file)
--- a/gcc/lra.cc
+++ b/gcc/lra.cc
@@ -1808,8 +1808,8 @@ lra_rtx_hash (rtx x)
 /* Bitmap used to put an insn on the stack only in one exemplar.  */
 static sbitmap lra_constraint_insn_stack_bitmap;
 
-/* The stack itself.  */
-vec<rtx_insn *> lra_constraint_insn_stack;
+/* Vectors used for the stack.  */
+static vec<rtx_insn *> lra_constraint_insn_stack, lra_constraint_insn_stack2;
 
 /* Put INSN on the stack.  If ALWAYS_UPDATE is true, always update the reg
    info for INSN, otherwise only update it if INSN is not already on the
@@ -1868,6 +1868,16 @@ lra_insn_stack_length (void)
   return lra_constraint_insn_stack.length ();
 }
 
+/* Purge the stack and return stack vector before purging.  */
+vec<rtx_insn *>
+lra_constraint_insn_stack_clear (void)
+{
+  std::swap (lra_constraint_insn_stack, lra_constraint_insn_stack2);
+  lra_constraint_insn_stack.truncate (0);
+  bitmap_clear (lra_constraint_insn_stack_bitmap);
+  return lra_constraint_insn_stack2;
+}
+
 /* Push insns FROM to TO (excluding it) going in reverse order.         */
 static void
 push_insns (rtx_insn *from, rtx_insn *to)
@@ -2458,6 +2468,7 @@ lra (FILE *f, int verbose)
      expensive when a lot of RTL changes are made.  */
   df_set_flags (DF_NO_INSN_RESCAN);
   lra_constraint_insn_stack.create (get_max_uid ());
+  lra_constraint_insn_stack2.create (get_max_uid ());
   lra_constraint_insn_stack_bitmap = sbitmap_alloc (get_max_uid ());
   bitmap_clear (lra_constraint_insn_stack_bitmap);
   lra_live_ranges_init ();
@@ -2635,6 +2646,7 @@ lra (FILE *f, int verbose)
   finish_reg_info ();
   sbitmap_free (lra_constraint_insn_stack_bitmap);
   lra_constraint_insn_stack.release ();
+  lra_constraint_insn_stack2.release ();
   finish_insn_recog_data ();
   lra_finish_equiv ();
   regstat_free_n_sets_and_refs ();