From 57424087e82db140c06d4ea73f9700d5291c5bc2 Mon Sep 17 00:00:00 2001
From: Xionghu Luo <xionghuluo@tencent.com>
Date: Thu, 9 Jun 2022 15:46:30 +0800
Subject: [PATCH] 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>
---
 gcc/gimple-if-to-switch.cc                    |  4 ++-
 .../gcc.dg/tree-ssa/if-to-switch-11.c         | 28 +++++++++++++++++++
 2 files changed, 31 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/if-to-switch-11.c

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" } } */