[gcc r14-4857] tree-optimization/111917 - bougs IL after guard hoisting

[Richard Biener <rguenth@gcc.gnu.org>]

https://gcc.gnu.org/g:d96bd4aade170fcd86f5f09b68b770dde798e631

commit r14-4857-gd96bd4aade170fcd86f5f09b68b770dde798e631
Author: Richard Biener <rguenther@suse.de>
Date:   Mon Oct 23 11:25:17 2023 +0200

    tree-optimization/111917 - bougs IL after guard hoisting
    
    The unswitching code to hoist guards inserts conditions in wrong
    places.  The following fixes this, simplifying code.
    
            PR tree-optimization/111917
            * tree-ssa-loop-unswitch.cc (hoist_guard): Always insert
            new conditional after last stmt.
    
            * gcc.dg/torture/pr111917.c: New testcase.

Diff:
---
 gcc/testsuite/gcc.dg/torture/pr111917.c | 23 +++++++++++++++++++++++
 gcc/tree-ssa-loop-unswitch.cc           |  5 +----
 2 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/torture/pr111917.c b/gcc/testsuite/gcc.dg/torture/pr111917.c
new file mode 100644
index 000000000000..532e30200b59
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr111917.c
@@ -0,0 +1,23 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-funswitch-loops" } */
+
+long t;
+long a() {
+  long b = t, c = t;
+  for (; b < 31; b++)
+    c <<= 1;
+  return c;
+}
+long t1;
+static
+int d() {
+  if (!t1)
+    return 0;
+e:
+f:
+  for (; a();)
+    ;
+  goto f;
+  return 0;
+}
+int main() { d(); }
diff --git a/gcc/tree-ssa-loop-unswitch.cc b/gcc/tree-ssa-loop-unswitch.cc
index 619b50fb4bb0..b4611ac82561 100644
--- a/gcc/tree-ssa-loop-unswitch.cc
+++ b/gcc/tree-ssa-loop-unswitch.cc
@@ -1455,10 +1455,7 @@ hoist_guard (class loop *loop, edge guard)
   cond_stmt = as_a <gcond *> (stmt);
   extract_true_false_edges_from_block (guard_bb, &te, &fe);
   /* Insert guard to PRE_HEADER.  */
-  if (!empty_block_p (pre_header))
-    gsi = gsi_last_bb (pre_header);
-  else
-    gsi = gsi_start_bb (pre_header);
+  gsi = gsi_last_bb (pre_header);
   /* Create copy of COND_STMT.  */
   new_cond_stmt = gimple_build_cond (gimple_cond_code (cond_stmt),
 				     gimple_cond_lhs (cond_stmt),