[gcc(refs/users/marxin/heads/PR106126-iftoswitch-side-effects)] if-to-switch: properly allow side effects only for first condition

[Martin Liska <marxin@gcc.gnu.org>]

https://gcc.gnu.org/g:a6b643af166a25b298f234d02929b80b03044a48

commit a6b643af166a25b298f234d02929b80b03044a48
Author: Martin Liska <mliska@suse.cz>
Date:   Thu Jun 30 15:00:17 2022 +0200

    if-to-switch: properly allow side effects only for first condition
    
    Properly allow side effects only for a first BB in a condition chain.
    
            PR tree-optimization/106126
    
    gcc/ChangeLog:
    
            * gimple-if-to-switch.cc (struct condition_info): Save
            has_side_effect.
            (find_conditions): Parse all BBs.
            (pass_if_to_switch::execute): Allow only side effects for first
            BB.
    
    gcc/testsuite/ChangeLog:
    
            * gcc.dg/tree-ssa/pr106126.c: New test.

Diff:
---
 gcc/gimple-if-to-switch.cc               | 20 +++++++++++---------
 gcc/testsuite/gcc.dg/tree-ssa/pr106126.c | 12 ++++++++++++
 2 files changed, 23 insertions(+), 9 deletions(-)

diff --git a/gcc/gimple-if-to-switch.cc b/gcc/gimple-if-to-switch.cc
index 70daae2003c..4441206c481 100644
--- a/gcc/gimple-if-to-switch.cc
+++ b/gcc/gimple-if-to-switch.cc
@@ -61,9 +61,11 @@ struct condition_info
 {
   typedef auto_vec<std::pair<gphi *, tree>> mapping_vec;
 
-  condition_info (gcond *cond): m_cond (cond), m_bb (gimple_bb (cond)),
-    m_forwarder_bb (NULL), m_ranges (), m_true_edge (NULL), m_false_edge (NULL),
-    m_true_edge_phi_mapping (), m_false_edge_phi_mapping ()
+  condition_info (gcond *cond, bool has_side_effect): m_cond (cond),
+    m_bb (gimple_bb (cond)), m_forwarder_bb (NULL), m_ranges (),
+    m_true_edge (NULL), m_false_edge (NULL),
+    m_true_edge_phi_mapping (), m_false_edge_phi_mapping (),
+    m_has_side_effect (has_side_effect)
   {
     m_ranges.create (0);
   }
@@ -80,6 +82,7 @@ struct condition_info
   edge m_false_edge;
   mapping_vec m_true_edge_phi_mapping;
   mapping_vec m_false_edge_phi_mapping;
+  bool m_has_side_effect;
 };
 
 /* Recond PHI mapping for an original edge E and save these into vector VEC.  */
@@ -389,16 +392,11 @@ find_conditions (basic_block bb,
   if (cond == NULL)
     return;
 
-  /* An empty conditions_in_bbs indicates we are processing the first
-     basic-block then no need check side effect.  */
-  if (!conditions_in_bbs->is_empty () && !no_side_effect_bb (bb))
-    return;
-
   tree lhs = gimple_cond_lhs (cond);
   tree rhs = gimple_cond_rhs (cond);
   tree_code code = gimple_cond_code (cond);
 
-  condition_info *info = new condition_info (cond);
+  condition_info *info = new condition_info (cond, !no_side_effect_bb (bb));
 
   gassign *def;
   if (code == NE_EXPR
@@ -536,6 +534,10 @@ pass_if_to_switch::execute (function *fun)
 	      if ((*info2)->m_false_edge != e)
 		break;
 
+	      /* Only the first BB in a chain can have a side effect.  */
+	      if (info->m_has_side_effect)
+		break;
+
 	      chain->m_entries.safe_push (*info2);
 	      bitmap_set_bit (seen_bbs, e->src->index);
 	      info = *info2;
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr106126.c b/gcc/testsuite/gcc.dg/tree-ssa/pr106126.c
new file mode 100644
index 00000000000..2f0fd44164b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr106126.c
@@ -0,0 +1,12 @@
+/* PR tree-optimization/106126 */
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+char *var_1;
+void pool_conda_matchspec() {
+  for (; var_1 && *var_1 &&
+         *var_1 != '<' && *var_1 != '>' &&
+         *var_1 != '!' && *var_1 != '~';)
+    if (*var_1 >= 'A' && *var_1 <= 'Z')
+      *var_1 += 'A';
+}