[gcc(refs/users/aoliva/heads/testme)] hardcmp: split before dispatch edge

[Alexandre Oliva <aoliva@gcc.gnu.org>]

https://gcc.gnu.org/g:361f4fcac4d9e948d22bb7ad87a0251aef5b03e0

commit 361f4fcac4d9e948d22bb7ad87a0251aef5b03e0
Author: Alexandre Oliva <oliva@adacore.com>
Date:   Wed Mar 23 20:16:22 2022 -0300

    hardcmp: split before dispatch edge
    
    If we harden a compare at the end of a block with an edge to the
    abnormal dispatch block, it won't have a single successor.  Arrange to
    split the block at its final stmt so as to have a single succ.
    
    
    for  gcc/ChangeLog
    
            PR middle-end/104975
            * gimple-harden-conditionals.cc
            (pass_harden_compares::execute): Force split in case of
            multiple edges.
    
    for  gcc/testsuite/ChangeLog
    
            PR middle-end/104975
            * gcc.dg/pr104975.c: New.

Diff:
---
 gcc/gimple-harden-conditionals.cc | 12 +++++++++---
 gcc/testsuite/gcc.dg/pr104975.c   | 20 ++++++++++++++++++++
 2 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/gcc/gimple-harden-conditionals.cc b/gcc/gimple-harden-conditionals.cc
index 6a5fc3fb9e1..be01f3ea8c4 100644
--- a/gcc/gimple-harden-conditionals.cc
+++ b/gcc/gimple-harden-conditionals.cc
@@ -509,10 +509,16 @@ pass_harden_compares::execute (function *fun)
 	gsi_insert_before (&gsi_split, asgnck, GSI_SAME_STMT);
 
 	/* We wish to insert a cond_expr after the compare, so arrange
-	   for it to be at the end of a block if it isn't.  */
-	if (!gsi_end_p (gsi_split))
+	   for it to be at the end of a block if it isn't, and for it
+	   to have a single successor in case there's more than
+	   one, as in PR104975.  */
+	if (!gsi_end_p (gsi_split)
+	    || !single_succ_p (gsi_bb (gsi_split)))
 	  {
-	    gsi_prev (&gsi_split);
+	    if (!gsi_end_p (gsi_split))
+	      gsi_prev (&gsi_split);
+	    else
+	      gsi_split = gsi_last_bb (gsi_bb (gsi_split));
 	    basic_block obb = gsi_bb (gsi_split);
 	    basic_block nbb = split_block (obb, gsi_stmt (gsi_split))->dest;
 	    gsi_next (&gsi_split);
diff --git a/gcc/testsuite/gcc.dg/pr104975.c b/gcc/testsuite/gcc.dg/pr104975.c
new file mode 100644
index 00000000000..04532fc4443
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr104975.c
@@ -0,0 +1,20 @@
+/* { dg-do compile } */
+/* { dg-options "-O1 -fharden-compares -fno-inline -fno-ipa-pure-const" } */
+
+__attribute__ ((pure, returns_twice)) int
+bar (int);
+
+int
+quux (void)
+{
+  return 0;
+}
+
+int
+foo (short int x)
+{
+  x = !x;
+  bar (quux ());
+
+  return x;
+}