[gcc r12-6140] Fix ICE in lsplit when built with -O3 -fno-guess-branch-probability [PR103793]

[gcc r12-6140] Fix ICE in lsplit when built with -O3 -fno-guess-branch-probability [PR103793]

[Xiong Hu Luo]

https://gcc.gnu.org/g:44372676e81358de29d5c853685a7664a95d8a96

commit r12-6140-g44372676e81358de29d5c853685a7664a95d8a96
Author: Xionghu Luo <luoxhu@linux.ibm.com>
Date:   Tue Dec 28 19:09:14 2021 -0600

    Fix ICE in lsplit when built with -O3 -fno-guess-branch-probability [PR103793]
    
    no-guess-branch-probability option requires profile_count scaling with
    initialized_p guard, use multiply instead of apply_scale, which will do
    the right thing to undefined probabilities and will not cause unnecesary
    roundoff errors and precision info loss.
    Also merge the missed part of r12-6086 of factor out function to avoid
    duplicate code.
    
    Regression testest pass on Power and X86.
    
    gcc/ChangeLog:
    
            PR tree-optimization/103793
            * tree-ssa-loop-split.c (fix_loop_bb_probability): New function.
            (split_loop): Use multiply to scale loop1's exit probability.
            (do_split_loop_on_cond): Call fix_loop_bb_probability.
    
    gcc/testsuite/ChangeLog:
    
            PR tree-optimization/103793
            * gcc.dg/pr103793.c: New test.

Diff:
---
 gcc/testsuite/gcc.dg/pr103793.c | 12 ++++++
 gcc/tree-ssa-loop-split.c       | 86 +++++++++++++++++------------------------
 2 files changed, 48 insertions(+), 50 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/pr103793.c b/gcc/testsuite/gcc.dg/pr103793.c
new file mode 100644
index 00000000000..d7ed721c973
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr103793.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-O3 -fno-guess-branch-probability" } */
+
+extern void bar (void);
+
+void
+foo (int x, int w)
+{
+  for (int y; y < w; y++)
+    if (y < x)
+      bar ();
+}
diff --git a/gcc/tree-ssa-loop-split.c b/gcc/tree-ssa-loop-split.c
index 33128061aab..3e1bbc84007 100644
--- a/gcc/tree-ssa-loop-split.c
+++ b/gcc/tree-ssa-loop-split.c
@@ -484,6 +484,39 @@ compute_new_first_bound (gimple_seq *stmts, class tree_niter_desc *niter,
   return newend;
 }
 
+/* Fix the two loop's bb count after split based on the split edge probability,
+   don't adjust the bbs dominated by true branches of that loop to avoid
+   dropping 1s down.  */
+static void
+fix_loop_bb_probability (class loop *loop1, class loop *loop2, edge true_edge,
+			 edge false_edge)
+{
+  update_ssa (TODO_update_ssa);
+
+  /* Proportion first loop's bb counts except those dominated by true
+     branch to avoid drop 1s down.  */
+  basic_block *bbs1, *bbs2;
+  bbs1 = get_loop_body (loop1);
+  unsigned j;
+  for (j = 0; j < loop1->num_nodes; j++)
+    if (bbs1[j] == loop1->latch
+	|| !dominated_by_p (CDI_DOMINATORS, bbs1[j], true_edge->dest))
+      bbs1[j]->count
+	= bbs1[j]->count.apply_probability (true_edge->probability);
+  free (bbs1);
+
+  /* Proportion second loop's bb counts except those dominated by false
+     branch to avoid drop 1s down.  */
+  basic_block bbi_copy = get_bb_copy (false_edge->dest);
+  bbs2 = get_loop_body (loop2);
+  for (j = 0; j < loop2->num_nodes; j++)
+    if (bbs2[j] == loop2->latch
+	|| !dominated_by_p (CDI_DOMINATORS, bbs2[j], bbi_copy))
+      bbs2[j]->count
+	= bbs2[j]->count.apply_probability (true_edge->probability.invert ());
+  free (bbs2);
+}
+
 /* Checks if LOOP contains an conditional block whose condition
    depends on which side in the iteration space it is, and if so
    splits the iteration space into two loops.  Returns true if the
@@ -610,38 +643,14 @@ 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);
 
-	update_ssa (TODO_update_ssa);
-
-	/* Proportion first loop's bb counts except those dominated by true
-	   branch to avoid drop 1s down.  */
-	basic_block *bbs1, *bbs2;
-	bbs1 = get_loop_body (loop1);
-	unsigned j;
-	for (j = 0; j < loop1->num_nodes; j++)
-	  if (bbs1[j] == loop1->latch
-	      || !dominated_by_p (CDI_DOMINATORS, bbs1[j], true_edge->dest))
-	    bbs1[j]->count
-	      = bbs1[j]->count.apply_probability (true_edge->probability);
-	free (bbs1);
+	fix_loop_bb_probability (loop1, loop2, true_edge, false_edge);
 
 	/* Fix first loop's exit probability after scaling.  */
 	edge exit_to_latch1 = single_pred_edge (loop1->latch);
-	exit_to_latch1->probability = exit_to_latch1->probability.apply_scale (
-	  true_edge->probability.to_reg_br_prob_base (), REG_BR_PROB_BASE);
+	exit_to_latch1->probability *= true_edge->probability;
 	single_exit (loop1)->probability
 	  = exit_to_latch1->probability.invert ();
 
-	/* Proportion second loop's bb counts except those dominated by false
-	   branch to avoid drop 1s down.  */
-	basic_block bbi_copy = get_bb_copy (false_edge->dest);
-	bbs2 = get_loop_body (loop2);
-	for (j = 0; j < loop2->num_nodes; j++)
-	  if (bbs2[j] == loop2->latch
-	      || !dominated_by_p (CDI_DOMINATORS, bbs2[j], bbi_copy))
-	    bbs2[j]->count = bbs2[j]->count.apply_probability (
-	      true_edge->probability.invert ());
-	free (bbs2);
-
 	/* Finally patch out the two copies of the condition to be always
 	   true/false (or opposite).  */
 	gcond *force_true = as_a<gcond *> (last_stmt (bbs[i]));
@@ -1570,40 +1579,17 @@ do_split_loop_on_cond (struct loop *loop1, edge invar_branch)
      between loop1 and loop2.  */
   connect_loop_phis (loop1, loop2, to_loop2);
 
-  update_ssa (TODO_update_ssa);
-
   edge true_edge, false_edge, skip_edge1, skip_edge2;
   extract_true_false_edges_from_block (cond_bb, &true_edge, &false_edge);
 
-  /* Proportion first loop's bb counts except those dominated by true
-     branch to avoid drop 1s down.  */
   skip_edge1 = true_invar ? false_edge : true_edge;
   skip_edge2 = true_invar ? true_edge : false_edge;
-  basic_block *bbs1, *bbs2;
-  bbs1 = get_loop_body (loop1);
-  unsigned j;
-  for (j = 0; j < loop1->num_nodes; j++)
-    if (bbs1[j] == loop1->latch
-	|| !dominated_by_p (CDI_DOMINATORS, bbs1[j], skip_edge1->dest))
-      bbs1[j]->count
-	= bbs1[j]->count.apply_probability (skip_edge1->probability);
-  free (bbs1);
+  fix_loop_bb_probability (loop1, loop2, skip_edge1, skip_edge2);
 
   /* Fix first loop's exit probability after scaling.  */
   to_loop1->probability = invar_branch->probability.invert ();
   to_loop2->probability = invar_branch->probability;
 
-  /* Proportion second loop's bb counts except those dominated by false
-     branch to avoid drop 1s down.  */
-  basic_block bbi_copy = get_bb_copy (skip_edge2->dest);
-  bbs2 = get_loop_body (loop2);
-  for (j = 0; j < loop2->num_nodes; j++)
-    if (bbs2[j] == loop2->latch
-	|| !dominated_by_p (CDI_DOMINATORS, bbs2[j], bbi_copy))
-      bbs2[j]->count
-	= bbs2[j]->count.apply_probability (skip_edge2->probability);
-  free (bbs2);
-
   free_original_copy_tables ();
 
   return true;