[gcc r13-1184] if-to-switch: Don't skip the first condition bb when find_conditions in if-to-switch [PR105740]

[Xiong Hu Luo <luoxhu@gcc.gnu.org>]

https://gcc.gnu.org/g:57424087e82db140c06d4ea73f9700d5291c5bc2

commit r13-1184-g57424087e82db140c06d4ea73f9700d5291c5bc2
Author: Xionghu Luo <xionghuluo@tencent.com>
Date:   Thu Jun 9 15:46:30 2022 +0800

    if-to-switch: Don't skip the first condition bb when find_conditions in if-to-switch [PR105740]
    
    The if condition is at last of first bb, so side effect statement in first BB
    doesn't matter, then the first if condition could also be folded to switch
    table.
    
    gcc/ChangeLog:
    
            PR target/105740
            * gimple-if-to-switch.cc (find_conditions): Don't skip the first
            condition bb.
    
    gcc/testsuite/ChangeLog:
    
            PR target/105740
            * gcc.dg/tree-ssa/if-to-switch-11.c: New test.
    
    Signed-off-by: Xionghu Luo <xionghuluo@tencent.com>

Diff:
---
 gcc/gimple-if-to-switch.cc                      |  4 +++-
 gcc/testsuite/gcc.dg/tree-ssa/if-to-switch-11.c | 28 +++++++++++++++++++++++++
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/gcc/gimple-if-to-switch.cc b/gcc/gimple-if-to-switch.cc
index 5dcfe5b77e0..ca276d790c3 100644
--- a/gcc/gimple-if-to-switch.cc
+++ b/gcc/gimple-if-to-switch.cc
@@ -389,7 +389,9 @@ find_conditions (basic_block bb,
   if (cond == NULL)
     return;
 
-  if (!no_side_effect_bb (bb))
+  /* 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);
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/if-to-switch-11.c b/gcc/testsuite/gcc.dg/tree-ssa/if-to-switch-11.c
new file mode 100644
index 00000000000..3dffee04812
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/if-to-switch-11.c
@@ -0,0 +1,28 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-iftoswitch-optimized" } */
+
+struct f {
+  int len;
+  int arr[4];
+};
+
+int
+test (struct f const *const f)
+{
+  if (f->arr[3] == 1) {
+    return 12;
+  } else if (f->arr[3] == 2) {
+    return 27;
+  } else if (f->arr[3] == 3) {
+    return 38;
+  } else if (f->arr[3] == 4) {
+    return 18;
+  } else if (f->arr[3] == 5) {
+    return 58;
+  } else if (f->arr[3] == 6) {
+    return 68;
+  }
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "Canonical GIMPLE case clusters: 1 2 3 4 5 6" "iftoswitch" } } */