[gcc r14-2850] loop-split improvements, part 2

[gcc r14-2850] loop-split improvements, part 2

[Jan Hubicka]

https://gcc.gnu.org/g:b24acae8f4d315a5b071ffc2574ce91c7a0800ca

commit r14-2850-gb24acae8f4d315a5b071ffc2574ce91c7a0800ca
Author: Jan Hubicka <jh@suse.cz>
Date:   Fri Jul 28 09:48:34 2023 +0200

    loop-split improvements, part 2
    
    this patch fixes profile update in the first case of loop splitting.
    The pass still gives up on very basic testcases:
    
    __attribute__ ((noinline,noipa))
    void test1 (int n)
    {
      if (n <= 0 || n > 100000)
        return;
      for (int i = 0; i <= n; i++)
        {
          if (i < n)
            do_something ();
          if (a[i])
            do_something2();
        }
    }
    
    Here I needed to do the conditoinal that enforces sane value range of n.
    The reason is that it gives up on:
          !number_of_iterations_exit (loop1, exit1, &niter, false, true)
    and without the conditonal we get assumption that n>=0 and not INT_MAX.
    I think from overflow we shold derive that INT_MAX test is not needed and since
    the loop does nothing for n<0 it is also just an paranoia.
    
    I am not sure how to fix this though :(.  In general the pass does not really
    need to compute iteration count.  It only needs to know what direction the IVs
    go so it can detect tests that fires in first part of iteration space.
    
    Rich, any idea what the correct test should be?
    
    In testcase:
      for (int i = 0; i < 200; i++)
        if (i < 150)
          do_something ();
        else
          do_something2 ();
    the old code did wrong update of the exit condition probabilities.
    We know that first loop iterates 150 times and the second loop 50 times
    and we get it by simply scaling loop body by the probability of inner test.
    
    With the patch we now get:
    
      <bb 2> [count: 1000]:
    
      <bb 3> [count: 150000]:    <- loop 1 correctly iterates 149 times
      # i_10 = PHI <i_7(8), 0(2)>
      do_something ();
      i_7 = i_10 + 1;
      if (i_7 <= 149)
        goto <bb 8>; [99.33%]
      else
        goto <bb 17>; [0.67%]
    
      <bb 8> [count: 149000]:
      goto <bb 3>; [100.00%]
    
      <bb 16> [count: 1000]:
      # i_15 = PHI <i_18(17)>
    
      <bb 9> [count: 49975]:    <- loop 2 should iterate 50 times but
                                   we are slightly wrong
      # i_3 = PHI <i_15(16), i_14(13)>
      do_something2 ();
      i_14 = i_3 + 1;
      if (i_14 != 200)
        goto <bb 13>; [98.00%]
      else
        goto <bb 7>; [2.00%]
    
      <bb 13> [count: 48975]:
      goto <bb 9>; [100.00%]
    
      <bb 17> [count: 1000]:   <- this test is always true becuase it is
                                  reached form bb 3
      # i_18 = PHI <i_7(3)>
      if (i_18 != 200)
        goto <bb 16>; [99.95%]
      else
        goto <bb 7>; [0.05%]
    
      <bb 7> [count: 1000]:
      return;
    
    The reason why we are slightly wrong is the condtion in bb17 that
    is always true but the pass does not konw it.
    
    Rich any idea how to do that?  I think connect_loops should work out
    the cas where the loop exit conditon is never satisfied at the time
    the splitted condition fails for first time.
    
    Before patch on hmmer we get a lot of mismatches:
    Profile report here claims:
    dump id |static mismat|dynamic mismatch                                     |
            |in count     |in count                  |time                      |
    lsplit  |      5    +5|   8151850567  +8151850567| 531506481006       +57.9%|
    ldist   |      9    +4|  15345493501  +7193642934| 606848841056       +14.2%|
    ifcvt   |     10    +1|  15487514871   +142021370| 689469797790       +13.6%|
    vect    |     35   +25|  17558425961  +2070911090| 517375405715       -25.0%|
    cunroll |     42    +7|  16898736178   -659689783| 452445796198        -4.9%|
    loopdone|     33    -9|   2678017188 -14220718990| 330969127663             |
    tracer  |     34    +1|   2678018710        +1522| 330613415364        +0.0%|
    fre     |     33    -1|   2676980249     -1038461| 330465677073        -0.0%|
    expand  |     28    -5|   2497468467   -179511782|--------------------------|
    
    With patch
    
    lsplit  |      0      |            0             | 328723360744        -2.3%|
    ldist   |      0      |            0             | 396193562452       +20.6%|
    ifcvt   |      1    +1|     71010686    +71010686| 478743508522       +20.8%|
    vect    |     14   +13|    697518955   +626508269| 299398068323       -37.5%|
    cunroll |     13    -1|    489349408   -208169547| 257777839725       -10.5%|
    loopdone|     11    -2|    402558559    -86790849| 201010712702             |
    tracer  |     13    +2|    402977200      +418641| 200651036623        +0.0%|
    fre     |     13      |    402622146      -355054| 200344398654        -0.2%|
    expand  |     11    -2|    333608636    -69013510|--------------------------|
    
    So no mismatches for lsplit and ldist and also lsplit thinks it improves speed by
    2.3% rather than regressig it by 57%.
    
    Update is still not perfect since we do not work out that the second loop
    never iterates.
    
    Ifcft wrecks profile by desing since it insert conditonals with both arms 100%
    that will be eliminated later after vect.  It is not clear to me what happens
    in vect though.
    
    Bootstrapped/regtested x86_64-linux, comitted.
    
    gcc/ChangeLog:
    
            PR middle-end/106923
            * tree-ssa-loop-split.cc (connect_loops): Change probability
            of the test preconditioning second loop to very_likely.
            (fix_loop_bb_probability): Handle correctly case where
            on of the arms of the conditional is empty.
            (split_loop): Fold the test guarding first condition to
            see if it is constant true; Set correct entry block
            probabilities of the split loops; determine correct loop
            eixt probabilities.
    
    gcc/testsuite/ChangeLog:
    
            PR middle-end/106293
            * gcc.dg/tree-prof/loop-split-1.c: New test.
            * gcc.dg/tree-prof/loop-split-2.c: New test.
            * gcc.dg/tree-prof/loop-split-3.c: New test.

Diff:
---
 gcc/testsuite/gcc.dg/tree-prof/loop-split-1.c | 33 +++++++++++
 gcc/testsuite/gcc.dg/tree-prof/loop-split-2.c | 36 ++++++++++++
 gcc/testsuite/gcc.dg/tree-prof/loop-split-3.c | 41 +++++++++++++
 gcc/tree-ssa-loop-split.cc                    | 84 ++++++++++++++++++++++-----
 4 files changed, 180 insertions(+), 14 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/tree-prof/loop-split-1.c b/gcc/testsuite/gcc.dg/tree-prof/loop-split-1.c
new file mode 100644
index 00000000000..46f7ae66fa3
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-prof/loop-split-1.c
@@ -0,0 +1,33 @@
+/* { dg-options "-O3 -fdump-tree-lsplit-details-blocks -fdump-tree-optimized-details-blocks" } */
+
+
+void
+__attribute__ ((noinline,noipa))
+do_something()
+{
+}
+void
+__attribute__ ((noinline,noipa))
+do_something2()
+{
+}
+
+__attribute__ ((noinline,noipa))
+void test1 (int n, int ga)
+{
+  for (int i = 0; i < 200; i++)
+	  if (i < 150)
+		  do_something ();
+	  else
+		  do_something2 ();
+}
+int
+main(int, char **)
+{
+	for (int i = 0 ; i < 1000; i++)
+	  test1(10, 10);
+	return 0;
+}
+/* { dg-final-use-not-autofdo { scan-tree-dump-times "Loop split" 1 "lsplit" } } */
+/* { dg-final-use-not-autofdo { scan-tree-dump-times "Invalid sum" 0 "lsplit" } } */
+/* { dg-final-use-not-autofdo { scan-tree-dump-times "Invalid sum" 0 "optimized" } } */
diff --git a/gcc/testsuite/gcc.dg/tree-prof/loop-split-2.c b/gcc/testsuite/gcc.dg/tree-prof/loop-split-2.c
new file mode 100644
index 00000000000..de2c9f58301
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-prof/loop-split-2.c
@@ -0,0 +1,36 @@
+/* { dg-options "-O3 -fdump-tree-lsplit-details-blocks -fdump-tree-optimized-details-blocks" } */
+
+int M = 100;
+
+void
+__attribute__ ((noinline,noipa))
+do_something()
+{
+}
+void
+__attribute__ ((noinline,noipa))
+do_something2()
+{
+}
+
+__attribute__ ((noinline,noipa))
+void test1 (int n)
+{
+  if (n <= 0 || n > 100000)
+        return; 
+  for (int i = 0; i <= n; i++)
+          if (i < n)
+                  do_something ();
+          else
+                  do_something2 ();
+}
+int
+main(int, char **)
+{
+        for (int i = 0 ; i < 1000; i++)
+          test1(M);
+        return 0;
+}
+/* { dg-final-use-not-autofdo { scan-tree-dump-times "Loop split" 1 "lsplit" } } */
+/* { dg-final-use-not-autofdo { scan-tree-dump-times "Invalid sum" 0 "lsplit" } } */
+/* { dg-final-use-not-autofdo { scan-tree-dump-times "Invalid sum" 0 "optimized" } } */
diff --git a/gcc/testsuite/gcc.dg/tree-prof/loop-split-3.c b/gcc/testsuite/gcc.dg/tree-prof/loop-split-3.c
new file mode 100644
index 00000000000..a88bc1f8663
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-prof/loop-split-3.c
@@ -0,0 +1,41 @@
+/* { dg-options "-O3 -fdump-tree-lsplit-details-blocks -fdump-tree-optimized-details-blocks" } */
+
+int M = 100;
+int a[1000];
+
+void
+__attribute__ ((noinline,noipa))
+do_something()
+{
+}
+void
+__attribute__ ((noinline,noipa))
+do_something2()
+{
+}
+
+__attribute__ ((noinline,noipa))
+void test1 (int n)
+{
+  if (n <= 0 || n > 100000)
+        return; 
+  for (int i = 0; i <= n; i++)
+    {
+      if (i < n)
+	do_something ();
+      if (a[i])
+	do_something2();
+    }
+}
+int
+main(int, char **)
+{
+  for (int i = 0 ; i < 1000; i+=3)
+    a[i]=1;
+  for (int i = 0 ; i < 1000; i++)
+    test1(M);
+  return 0;
+}
+/* { dg-final-use-not-autofdo { scan-tree-dump-times "Loop split" 1 "lsplit" } } */
+/* { dg-final-use-not-autofdo { scan-tree-dump-times "Invalid sum" 0 "lsplit" } } */
+/* { dg-final-use-not-autofdo { scan-tree-dump-times "Invalid sum" 0 "optimized" } } */
diff --git a/gcc/tree-ssa-loop-split.cc b/gcc/tree-ssa-loop-split.cc
index f441f3fe1b5..70cd0aaefa7 100644
--- a/gcc/tree-ssa-loop-split.cc
+++ b/gcc/tree-ssa-loop-split.cc
@@ -41,6 +41,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "cfghooks.h"
 #include "gimple-fold.h"
 #include "gimplify-me.h"
+#include "print-tree.h"
 
 /* This file implements two kinds of loop splitting.
 
@@ -355,7 +356,7 @@ connect_loops (class loop *loop1, class loop *loop2)
       new_e->flags |= EDGE_TRUE_VALUE;
     }
 
-  new_e->probability = profile_probability::likely ();
+  new_e->probability = profile_probability::very_likely ();
   skip_e->probability = new_e->probability.invert ();
 
   return new_e;
@@ -496,6 +497,8 @@ fix_loop_bb_probability (class loop *loop1, class loop *loop2, edge true_edge,
   unsigned j;
   for (j = 0; j < loop1->num_nodes; j++)
     if (bbs1[j] == loop1->latch
+	/* Watch for case where the true conditional is empty.  */
+	|| !single_pred_p (true_edge->dest)
 	|| !dominated_by_p (CDI_DOMINATORS, bbs1[j], true_edge->dest))
       bbs1[j]->count
 	= bbs1[j]->count.apply_probability (true_edge->probability);
@@ -507,6 +510,8 @@ fix_loop_bb_probability (class loop *loop1, class loop *loop2, edge true_edge,
   bbs2 = get_loop_body (loop2);
   for (j = 0; j < loop2->num_nodes; j++)
     if (bbs2[j] == loop2->latch
+	/* Watch for case where the flase conditional is empty.  */
+	|| !single_pred_p (bbi_copy)
 	|| !dominated_by_p (CDI_DOMINATORS, bbs2[j], bbi_copy))
       bbs2[j]->count
 	= bbs2[j]->count.apply_probability (true_edge->probability.invert ());
@@ -564,6 +569,7 @@ split_loop (class loop *loop1)
   for (i = 0; i < loop1->num_nodes; i++)
     if ((guard_iv = split_at_bb_p (loop1, bbs[i], &border, &iv)))
       {
+	profile_count entry_count = loop_preheader_edge (loop1)->count ();
 	/* Handling opposite steps is not implemented yet.  Neither
 	   is handling different step sizes.  */
 	if ((tree_int_cst_sign_bit (iv.step)
@@ -610,7 +616,8 @@ split_loop (class loop *loop1)
 	if (stmts2)
 	  gsi_insert_seq_on_edge_immediate (loop_preheader_edge (loop1),
 					    stmts2);
-	tree cond = build2 (guard_code, boolean_type_node, guard_init, border);
+	tree cond = fold_build2 (guard_code, boolean_type_node,
+				 guard_init, border);
 	if (!initial_true)
 	  cond = fold_build1 (TRUTH_NOT_EXPR, boolean_type_node, cond);
 
@@ -622,13 +629,71 @@ split_loop (class loop *loop1)
 	initialize_original_copy_tables ();
 	basic_block cond_bb;
 
+	profile_probability loop1_prob
+	  = integer_onep (cond) ? profile_probability::always ()
+				: true_edge->probability;
+	/* TODO: It is commonly a case that we know that both loops will be
+	   entered.  very_likely below is the probability that second loop will
+	   be entered given by connect_loops.  We should work out the common
+	   case it is always true.  */
 	class loop *loop2 = loop_version (loop1, cond, &cond_bb,
-					  true_edge->probability,
-					  true_edge->probability.invert (),
+					  loop1_prob,
+					  /* Pass always as we will later
+					     redirect first loop to second
+					     loop.  */
 					  profile_probability::always (),
 					  profile_probability::always (),
+					  profile_probability::very_likely (),
 					  true);
 	gcc_assert (loop2);
+	/* Correct probability of edge  cond_bb->preheader_of_loop2.  */
+	single_pred_edge
+		(loop_preheader_edge (loop2)->src)->probability
+			= loop1_prob.invert ();
+
+	fix_loop_bb_probability (loop1, loop2, true_edge, false_edge);
+
+	/* Fix loop's exit probability after scaling.  */
+
+	if (entry_count.initialized_p () && entry_count.nonzero_p ())
+	  {
+	    edge exit_to_latch1;
+	    if (EDGE_SUCC (exit1->src, 0) == exit1)
+	      exit_to_latch1 = EDGE_SUCC (exit1->src, 1);
+	    else
+	      exit_to_latch1 = EDGE_SUCC (exit1->src, 0);
+	    if (exit1->src->count.nonzero_p ())
+	      {
+		/* First loop is entered loop1_prob * entry_count times
+		   and it needs to exit the same number of times.  */
+		exit1->probability
+			= entry_count.apply_probability
+				(loop1_prob).probability_in (exit1->src->count);
+		exit_to_latch1->probability = exit1->probability.invert ();
+		scale_dominated_blocks_in_loop (loop1, exit1->src,
+						exit_to_latch1->count (),
+						exit_to_latch1->dest->count);
+	      }
+
+	    edge exit_to_latch2, exit2 = single_exit (loop2);
+	    if (EDGE_SUCC (exit2->src, 0) == exit2)
+	      exit_to_latch2 = EDGE_SUCC (exit2->src, 1);
+	    else
+	      exit_to_latch2 = EDGE_SUCC (exit2->src, 0);
+	    if (exit2->src->count.nonzero_p ())
+	      {
+		/* Second loop is entered very_likely * entry_count times
+		   and it needs to exit the same number of times.  */
+		exit2->probability
+			= entry_count.apply_probability
+				(profile_probability::very_likely ())
+				.probability_in (exit2->src->count);
+		exit_to_latch2->probability = exit2->probability.invert ();
+		scale_dominated_blocks_in_loop (loop2, exit2->src,
+						exit_to_latch2->count (),
+						exit_to_latch2->dest->count);
+	      }
+	  }
 
 	edge new_e = connect_loops (loop1, loop2);
 	connect_loop_phis (loop1, loop2, new_e);
@@ -647,16 +712,7 @@ split_loop (class loop *loop1)
 	tree guard_next = PHI_ARG_DEF_FROM_EDGE (phi, loop_latch_edge (loop1));
 	patch_loop_exit (loop1, guard_stmt, guard_next, newend, initial_true);
 
-	fix_loop_bb_probability (loop1, loop2, true_edge, false_edge);
-
-	/* Fix first loop's exit probability after scaling.  */
-	edge exit_to_latch1;
-	if (EDGE_SUCC (exit1->src, 0) == exit1)
-	  exit_to_latch1 = EDGE_SUCC (exit1->src, 1);
-	else
-	  exit_to_latch1 = EDGE_SUCC (exit1->src, 0);
-	exit_to_latch1->probability *= true_edge->probability;
-	exit1->probability = exit_to_latch1->probability.invert ();
+	/* TODO: Update any_esitmate and upper bounds.  */
 
 	/* Finally patch out the two copies of the condition to be always
 	   true/false (or opposite).  */