[gcc r13-3753] tree-ssa-sink: do not touch calls that return twice

[gcc r13-3753] tree-ssa-sink: do not touch calls that return twice

[Alexander Monakov]

https://gcc.gnu.org/g:5d060d8b0477ff4911f41c816281daaa24b41a13

commit r13-3753-g5d060d8b0477ff4911f41c816281daaa24b41a13
Author: Alexander Monakov <amonakov@ispras.ru>
Date:   Mon Nov 7 15:33:01 2022 +0300

    tree-ssa-sink: do not touch calls that return twice
    
    Avoid moving pure/const calls that may return twice in tree-ssa-sink:
    properly redirecting the associated abnormal edge is non-trivial.
    
    gcc/ChangeLog:
    
            PR tree-optimization/107505
            * tree-ssa-sink.cc (statement_sink_location): Additionally
            reject ECF_RETURNS_TWICE calls.
    
    gcc/testsuite/ChangeLog:
    
            PR tree-optimization/107505
            * gcc.dg/pr107505.c: New test.

Diff:
---
 gcc/testsuite/gcc.dg/pr107505.c | 26 ++++++++++++++++++++++++++
 gcc/tree-ssa-sink.cc            |  5 +++--
 2 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/pr107505.c b/gcc/testsuite/gcc.dg/pr107505.c
new file mode 100644
index 00000000000..01270eac91c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr107505.c
@@ -0,0 +1,26 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fno-guess-branch-probability" } */
+
+int n;
+
+void
+bar (void);
+
+__attribute__ ((noinline, returns_twice)) int
+zero (void)
+{
+  return 0;
+}
+
+void
+foo (void)
+{
+  int a = zero ();
+
+  for (n = 0; n < 2; ++n)
+    {
+    }
+
+  if (a)
+    bar ();
+}
diff --git a/gcc/tree-ssa-sink.cc b/gcc/tree-ssa-sink.cc
index 9213052017a..eb7c2e6819c 100644
--- a/gcc/tree-ssa-sink.cc
+++ b/gcc/tree-ssa-sink.cc
@@ -263,12 +263,13 @@ statement_sink_location (gimple *stmt, basic_block frombb,
 
   *zero_uses_p = false;
 
-  /* We only can sink assignments and non-looping const/pure calls.  */
+  /* We only can sink assignments and const/pure calls that are guaranteed
+     to return exactly once.  */
   int cf;
   if (!is_gimple_assign (stmt)
       && (!is_gimple_call (stmt)
 	  || !((cf = gimple_call_flags (stmt)) & (ECF_CONST|ECF_PURE))
-	  || (cf & ECF_LOOPING_CONST_OR_PURE)))
+	  || (cf & (ECF_LOOPING_CONST_OR_PURE|ECF_RETURNS_TWICE))))
     return false;
 
   /* We only can sink stmts with a single definition.  */