[gcc r14-4944] [RA]: Modfify cost calculation for dealing with equivalences

[gcc r14-4944] [RA]: Modfify cost calculation for dealing with equivalences

[Vladimir Makarov]

https://gcc.gnu.org/g:f55cdce3f8dd8503e080e35be59c5f5390f6d95e

commit r14-4944-gf55cdce3f8dd8503e080e35be59c5f5390f6d95e
Author: Vladimir N. Makarov <vmakarov@redhat.com>
Date:   Thu Oct 26 09:50:40 2023 -0400

    [RA]: Modfify cost calculation for dealing with equivalences
    
    RISCV target developers reported that pseudos with equivalence used in
    a loop can be spilled.  Simple changes of heuristics of cost
    calculation of pseudos with equivalence or even ignoring equivalences
    resulted in numerous testsuite failures on different targets or worse
    spec2017 performance.  This patch implements more sophisticated cost
    calculations of pseudos with equivalences.  The patch does not change
    RA behaviour for targets still using the old reload pass instead of
    LRA.  The patch solves the reported problem and improves x86-64
    specint2017 a bit (specfp2017 performance stays the same).  The patch
    takes into account how the equivalence will be used: will it be
    integrated into the user insns or require an input reload insn.  It
    requires additional pass over insns.  To compensate RA slow down, the
    patch removes a pass over insns in the reload pass used by IRA before.
    This also decouples IRA from reload more and will help to remove the
    reload pass in the future if it ever happens.
    
    gcc/ChangeLog:
    
            * dwarf2out.cc (reg_loc_descriptor): Use lra_eliminate_regs when
            LRA is used.
            * ira-costs.cc: Include regset.h.
            (equiv_can_be_consumed_p, get_equiv_regno, calculate_equiv_gains):
            New functions.
            (find_costs_and_classes): Call calculate_equiv_gains and redefine
            mem_cost of pseudos with equivs when LRA is used.
            * var-tracking.cc: Include ira.h and lra.h.
            (vt_initialize): Use lra_eliminate_regs when LRA is used.

Diff:
---
 gcc/dwarf2out.cc    |   4 +-
 gcc/ira-costs.cc    | 169 ++++++++++++++++++++++++++++++++++++++++++++++++++--
 gcc/var-tracking.cc |  14 ++++-
 3 files changed, 179 insertions(+), 8 deletions(-)

diff --git a/gcc/dwarf2out.cc b/gcc/dwarf2out.cc
index 0ea73bf782e5..1e0cec66c5e9 100644
--- a/gcc/dwarf2out.cc
+++ b/gcc/dwarf2out.cc
@@ -14311,7 +14311,9 @@ reg_loc_descriptor (rtx rtl, enum var_init_status initialized)
      argument pointer and soft frame pointer rtx's.
      Use DW_OP_fbreg offset DW_OP_stack_value in this case.  */
   if ((rtl == arg_pointer_rtx || rtl == frame_pointer_rtx)
-      && eliminate_regs (rtl, VOIDmode, NULL_RTX) != rtl)
+      && (ira_use_lra_p
+	  ? lra_eliminate_regs (rtl, VOIDmode, NULL_RTX)
+	  : eliminate_regs (rtl, VOIDmode, NULL_RTX)) != rtl)
     {
       dw_loc_descr_ref result = NULL;
 
diff --git a/gcc/ira-costs.cc b/gcc/ira-costs.cc
index d9e700e89473..a59d45a6e24c 100644
--- a/gcc/ira-costs.cc
+++ b/gcc/ira-costs.cc
@@ -30,6 +30,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "tm_p.h"
 #include "insn-config.h"
 #include "regs.h"
+#include "regset.h"
 #include "ira.h"
 #include "ira-int.h"
 #include "addresses.h"
@@ -1757,6 +1758,145 @@ process_bb_node_for_costs (ira_loop_tree_node_t loop_tree_node)
     process_bb_for_costs (bb);
 }
 
+/* Check that reg REGNO can be changed by TO in INSN.  Return true in case the
+   result insn would be valid one.  */
+static bool
+equiv_can_be_consumed_p (int regno, rtx to, rtx_insn *insn)
+{
+  validate_replace_src_group (regno_reg_rtx[regno], to, insn);
+  bool res = verify_changes (0);
+  cancel_changes (0);
+  return res;
+}
+
+/* Return true if X contains a pseudo with equivalence.  In this case also
+   return the pseudo through parameter REG.  If the pseudo is a part of subreg,
+   return the subreg through parameter SUBREG.  */
+
+static bool
+get_equiv_regno (rtx x, int &regno, rtx &subreg)
+{
+  subreg = NULL_RTX;
+  if (GET_CODE (x) == SUBREG)
+    {
+      subreg = x;
+      x = SUBREG_REG (x);
+    }
+  if (REG_P (x)
+      && (ira_reg_equiv[REGNO (x)].memory != NULL
+	  || ira_reg_equiv[REGNO (x)].constant != NULL))
+    {
+      regno = REGNO (x);
+      return true;
+    }
+  RTX_CODE code = GET_CODE (x);
+  const char *fmt = GET_RTX_FORMAT (code);
+
+  for (int i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
+    if (fmt[i] == 'e')
+      {
+	if (get_equiv_regno (XEXP (x, i), regno, subreg))
+	  return true;
+      }
+    else if (fmt[i] == 'E')
+      {
+	for (int j = 0; j < XVECLEN (x, i); j++)
+	  if (get_equiv_regno (XVECEXP (x, i, j), regno, subreg))
+	    return true;
+      }
+  return false;
+}
+
+/* A pass through the current function insns.  Calculate costs of using
+   equivalences for pseudos and store them in regno_equiv_gains.  */
+
+static void
+calculate_equiv_gains (void)
+{
+  basic_block bb;
+  int regno, freq, cost;
+  rtx subreg;
+  rtx_insn *insn;
+  machine_mode mode;
+  enum reg_class rclass;
+  bitmap_head equiv_pseudos;
+
+  ira_assert (allocno_p);
+  bitmap_initialize (&equiv_pseudos, &reg_obstack);
+  for (regno = max_reg_num () - 1; regno >= FIRST_PSEUDO_REGISTER; regno--)
+    if (ira_reg_equiv[regno].init_insns != NULL
+	&& (ira_reg_equiv[regno].memory != NULL
+	    || (ira_reg_equiv[regno].constant != NULL
+		/* Ignore complicated constants which probably will be placed
+		   in memory:  */
+		&& GET_CODE (ira_reg_equiv[regno].constant) != CONST_DOUBLE
+		&& GET_CODE (ira_reg_equiv[regno].constant) != CONST_VECTOR
+		&& GET_CODE (ira_reg_equiv[regno].constant) != LABEL_REF)))
+      {
+	rtx_insn_list *x;
+	for (x = ira_reg_equiv[regno].init_insns; x != NULL; x = x->next ())
+	  {
+	    insn = x->insn ();
+	    rtx set = single_set (insn);
+
+	    if (set == NULL_RTX || SET_DEST (set) != regno_reg_rtx[regno])
+	      break;
+	    bb = BLOCK_FOR_INSN (insn);
+	    ira_curr_regno_allocno_map
+	      = ira_bb_nodes[bb->index].parent->regno_allocno_map;
+	    mode = PSEUDO_REGNO_MODE (regno);
+	    rclass = pref[COST_INDEX (regno)];
+	    ira_init_register_move_cost_if_necessary (mode);
+	    if (ira_reg_equiv[regno].memory != NULL)
+	      cost = ira_memory_move_cost[mode][rclass][1];
+	    else
+	      cost = ira_register_move_cost[mode][rclass][rclass];
+	    freq = REG_FREQ_FROM_BB (bb);
+	    regno_equiv_gains[regno] += cost * freq;
+	  }
+	if (x != NULL)
+	  /* We found complicated equiv or reverse equiv mem=reg.  Ignore
+	     them.  */
+	  regno_equiv_gains[regno] = 0;
+	else
+	  bitmap_set_bit (&equiv_pseudos, regno);
+      }
+
+  FOR_EACH_BB_FN (bb, cfun)
+    {
+      freq = REG_FREQ_FROM_BB (bb);
+      ira_curr_regno_allocno_map
+	= ira_bb_nodes[bb->index].parent->regno_allocno_map;
+      FOR_BB_INSNS (bb, insn)
+	{
+	  if (!INSN_P (insn) || !get_equiv_regno (PATTERN (insn), regno, subreg)
+	      || !bitmap_bit_p (&equiv_pseudos, regno))
+	    continue;
+	  rtx subst = ira_reg_equiv[regno].memory;
+
+	  if (subst == NULL)
+	    subst = ira_reg_equiv[regno].constant;
+	  ira_assert (subst != NULL);
+	  mode = PSEUDO_REGNO_MODE (regno);
+	  ira_init_register_move_cost_if_necessary (mode);
+	  bool consumed_p = equiv_can_be_consumed_p (regno, subst, insn);
+
+	  rclass = pref[COST_INDEX (regno)];
+	  if (MEM_P (subst)
+	      /* If it is a change of constant into double for example, the
+		 result constant probably will be placed in memory.  */
+	      || (subreg != NULL_RTX && !INTEGRAL_MODE_P (GET_MODE (subreg))))
+	    cost = ira_memory_move_cost[mode][rclass][1] + (consumed_p ? 0 : 1);
+	  else if (consumed_p)
+	    continue;
+	  else
+	    cost = ira_register_move_cost[mode][rclass][rclass];
+	  regno_equiv_gains[regno] -= cost * freq;
+	}
+    }
+  bitmap_clear (&equiv_pseudos);
+}
+
 /* Find costs of register classes and memory for allocnos or pseudos
    and their best costs.  Set up preferred, alternative and allocno
    classes for pseudos.  */
@@ -1855,6 +1995,12 @@ find_costs_and_classes (FILE *dump_file)
       if (pass == 0)
 	pref = pref_buffer;
 
+      if (ira_use_lra_p && allocno_p && pass == 1)
+	/* It is a pass through all insns.  So do it once and only for RA (not
+	   for insn scheduler) when we already found preferable pseudo register
+	   classes on the previous pass.  */
+	calculate_equiv_gains ();
+
       /* Now for each allocno look at how desirable each class is and
 	 find which class is preferred.  */
       for (i = max_reg_num () - 1; i >= FIRST_PSEUDO_REGISTER; i--)
@@ -1947,6 +2093,17 @@ find_costs_and_classes (FILE *dump_file)
 	    }
 	  if (i >= first_moveable_pseudo && i < last_moveable_pseudo)
 	    i_mem_cost = 0;
+	  else if (ira_use_lra_p)
+	    {
+	      if (equiv_savings > 0)
+		{
+		  i_mem_cost = 0;
+		  if (ira_dump_file != NULL && internal_flag_ira_verbose > 5)
+		    fprintf (ira_dump_file,
+			     "   Use MEM for r%d as the equiv savings is %d\n",
+			     i, equiv_savings);
+		}
+	    }
 	  else if (equiv_savings < 0)
 	    i_mem_cost = -equiv_savings;
 	  else if (equiv_savings > 0)
@@ -2395,7 +2552,10 @@ ira_costs (void)
   total_allocno_costs = (struct costs *) ira_allocate (max_struct_costs_size
 						       * ira_allocnos_num);
   initiate_regno_cost_classes ();
-  calculate_elim_costs_all_insns ();
+  if (!ira_use_lra_p)
+    /* Process equivs in reload to update costs through hook
+       ira_adjust_equiv_reg_cost.  */
+    calculate_elim_costs_all_insns ();
   find_costs_and_classes (ira_dump_file);
   setup_allocno_class_and_costs ();
   finish_regno_cost_classes ();
@@ -2520,13 +2680,14 @@ ira_tune_allocno_costs (void)
     }
 }
 
-/* Add COST to the estimated gain for eliminating REGNO with its
-   equivalence.  If COST is zero, record that no such elimination is
-   possible.  */
+/* A hook from the reload pass.  Add COST to the estimated gain for eliminating
+   REGNO with its equivalence.  If COST is zero, record that no such
+   elimination is possible.  */
 
 void
 ira_adjust_equiv_reg_cost (unsigned regno, int cost)
 {
+  ira_assert (!ira_use_lra_p);
   if (cost == 0)
     regno_equiv_gains[regno] = 0;
   else
diff --git a/gcc/var-tracking.cc b/gcc/var-tracking.cc
index d8dafa5481af..4a81ccbe4867 100644
--- a/gcc/var-tracking.cc
+++ b/gcc/var-tracking.cc
@@ -107,6 +107,8 @@
 #include "cfgrtl.h"
 #include "cfganal.h"
 #include "reload.h"
+#include "ira.h"
+#include "lra.h"
 #include "calls.h"
 #include "tree-dfa.h"
 #include "tree-ssa.h"
@@ -10131,7 +10133,9 @@ vt_initialize (void)
 #else
       reg = arg_pointer_rtx;
 #endif
-      elim = eliminate_regs (reg, VOIDmode, NULL_RTX);
+      elim = (ira_use_lra_p
+	      ? lra_eliminate_regs (reg, VOIDmode, NULL_RTX)
+	      : eliminate_regs (reg, VOIDmode, NULL_RTX));
       if (elim != reg)
 	{
 	  if (GET_CODE (elim) == PLUS)
@@ -10151,7 +10155,9 @@ vt_initialize (void)
       reg = arg_pointer_rtx;
       fp_cfa_offset = ARG_POINTER_CFA_OFFSET (current_function_decl);
 #endif
-      elim = eliminate_regs (reg, VOIDmode, NULL_RTX);
+      elim = (ira_use_lra_p
+	      ? lra_eliminate_regs (reg, VOIDmode, NULL_RTX)
+	      : eliminate_regs (reg, VOIDmode, NULL_RTX));
       if (elim != reg)
 	{
 	  if (GET_CODE (elim) == PLUS)
@@ -10183,7 +10189,9 @@ vt_initialize (void)
 #else
       reg = arg_pointer_rtx;
 #endif
-      elim = eliminate_regs (reg, VOIDmode, NULL_RTX);
+      elim = (ira_use_lra_p
+	      ? lra_eliminate_regs (reg, VOIDmode, NULL_RTX)
+	      : eliminate_regs (reg, VOIDmode, NULL_RTX));
       if (elim != reg)
 	{
 	  if (GET_CODE (elim) == PLUS)