path: root/0086-Modfify-cost-calculation-for-dealing-with-equivalenc.patch

From c546aad5d38165e2962456525a0f6a427e03583b Mon Sep 17 00:00:00 2001
From: "Vladimir N. Makarov" <vmakarov@redhat.com>
Date: Thu, 26 Oct 2023 09:50:40 -0400
Subject: [PATCH 31/32] 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.
---
 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 0a5c081d8..f0f6f4fd4 100644
--- a/gcc/dwarf2out.cc
+++ b/gcc/dwarf2out.cc
@@ -14263,7 +14263,9 @@ 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 642fda529..c79311783 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"
@@ -1750,6 +1751,145 @@ 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.  */
@@ -1848,6 +1988,12 @@ 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--)
@@ -1940,6 +2086,17 @@ 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)
@@ -2378,7 +2535,10 @@ 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 ();
@@ -2503,13 +2663,14 @@ 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 7c3ad0a55..b10c8c1eb 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"
@@ -10133,7 +10135,9 @@ 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)
@@ -10153,7 +10157,9 @@ 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)
@@ -10185,7 +10191,9 @@ 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)
-- 
2.28.0.windows.1