gimple: sccopy: Prune removed statements from SCCs [PR117919]

While writing the sccopy pass I didn't realize that 'replace_uses_by ()' can
remove portions of the CFG.  This happens when replacing arguments of some
statement results in the removal of an EH edge.  Because of this sccopy can
then work with GIMPLE statements that aren't part of the IR anymore.  In
PR117919 this triggered an assertion within the pass which assumes that
statements the pass works with are reachable.

This patch tells the pass to notice when a statement isn't in the IR anymore
and remove it from it's worklist.

	PR tree-optimization/117919

gcc/ChangeLog:

	* gimple-ssa-sccopy.cc (scc_copy_prop::propagate): Prune
	statements that 'replace_uses_by ()' removed.

gcc/testsuite/ChangeLog:

	* g++.dg/pr117919.C: New test.

Signed-off-by: Filip Kastl <fkastl@suse.cz>

2 files changed, 65 insertions, 0 deletions

diff --git a/gcc/gimple-ssa-sccopy.cc b/gcc/gimple-ssa-sccopy.cc
index 9f25fba..7ffb571 100644
--- a/gcc/gimple-ssa-sccopy.cc
+++ b/gcc/gimple-ssa-sccopy.cc
@@ -568,6 +568,19 @@ scc_copy_prop::propagate ()
     {
       vec<gimple *> scc = worklist.pop ();
 
+      /* When we do 'replace_scc_by_value' it may happen that some EH edges
+	 get removed.  That means parts of CFG get removed.  Those may
+	 contain copy statements.  For that reason we prune SCCs here.  */
+      unsigned i;
+      for (i = 0; i < scc.length (); i++)
+	if (gimple_bb (scc[i]) == NULL)
+	  scc.unordered_remove (i);
+      if (scc.is_empty ())
+	{
+	  scc.release ();
+	  continue;
+	}
+
       auto_vec<gimple *> inner;
       hash_set<tree> outer_ops;
       tree last_outer_op = NULL_TREE;
diff --git a/gcc/testsuite/g++.dg/pr117919.C b/gcc/testsuite/g++.dg/pr117919.C
new file mode 100644
index 0000000..fa2d9c9
--- /dev/null
+++ b/gcc/testsuite/g++.dg/pr117919.C
@@ -0,0 +1,52 @@
+/* PR tree-optimization/117919 */
+/* { dg-do compile } */
+/* { dg-options "-O1 -fno-tree-forwprop -fnon-call-exceptions --param=early-inlining-insns=192 -std=c++20" } */
+
+char _M_p, _M_construct___beg;
+struct _Alloc_hider {
+  _Alloc_hider(char);
+};
+long _M_string_length;
+void _M_destroy();
+void _S_copy_chars(char *, char *, char *) noexcept;
+char _M_local_data();
+struct Trans_NS___cxx11_basic_string {
+  _Alloc_hider _M_dataplus;
+  bool _M_is_local() {
+    if (_M_local_data())
+      if (_M_string_length)
+        return true;
+    return false;
+  }
+  void _M_dispose() {
+    if (!_M_is_local())
+      _M_destroy();
+  }
+  char *_M_construct___end;
+  Trans_NS___cxx11_basic_string(Trans_NS___cxx11_basic_string &)
+      : _M_dataplus(0) {
+    struct _Guard {
+      ~_Guard() { _M_guarded->_M_dispose(); }
+      Trans_NS___cxx11_basic_string *_M_guarded;
+    } __guard0;
+    _S_copy_chars(&_M_p, &_M_construct___beg, _M_construct___end);
+  }
+};
+namespace filesystem {
+struct path {
+  path();
+  Trans_NS___cxx11_basic_string _M_pathname;
+};
+} // namespace filesystem
+struct FileWriter {
+  filesystem::path path;
+  FileWriter() : path(path) {}
+};
+struct LanguageFileWriter : FileWriter {
+  LanguageFileWriter(filesystem::path) {}
+};
+int
+main() {
+  filesystem::path output_file;
+  LanguageFileWriter writer(output_file);
+}