From a1cd4d52d6ef90b977fb2d80c1cf17f3efa5b01d Mon Sep 17 00:00:00 2001
From: Richard Biener <rguenther@suse.de>
Date: Fri, 19 Aug 2022 15:11:14 +0200
Subject: [PATCH] tree-optimization/105646 - re-interpret always executed in
 uninit diag

The following fixes PR105646, not diagnosing

int f1();
int f3(){
    auto const & a = f1();
    bool v3{v3};
    return a;
}

with optimization because the early uninit diagnostic pass only
diagnoses always executed cases.  The patch does this by
re-interpreting what always executed means and choosing to
ignore exceptional and abnormal control flow for this.  At the
same time it improves things as suggested in a comment - when
the value-numbering run done without optimizing figures there's
a fallthru path, consider blocks on it as always executed.

	PR tree-optimization/105646
	* tree-ssa-uninit.cc (warn_uninitialized_vars): Pre-compute
	the set of fallthru reachable blocks from function entry
	and use that to determine wlims.always_executed.

	* g++.dg/uninit-pr105646.C: New testcase.
---
 gcc/testsuite/g++.dg/uninit-pr105646.C | 17 +++++++++++++++++
 gcc/tree-ssa-uninit.cc                 | 10 ++++++++--
 2 files changed, 25 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/uninit-pr105646.C

diff --git a/gcc/testsuite/g++.dg/uninit-pr105646.C b/gcc/testsuite/g++.dg/uninit-pr105646.C
new file mode 100644
index 0000000..48ceb98
--- /dev/null
+++ b/gcc/testsuite/g++.dg/uninit-pr105646.C
@@ -0,0 +1,17 @@
+// { dg-do compile }
+// { dg-require-effective-target c++11 }
+// { dg-options "-O2 -Wuninitialized" }
+
+int f1();
+int f2(){
+    bool v2{v2}; // { dg-warning "is used uninitialized" }
+    auto const & a = f1();
+    return a;
+}
+int f3(){
+    auto const & a = f1();
+    // Diagnose the following when optimizing and as unconditional
+    // uninitialized use despite f1 possibly throwing
+    bool v3{v3}; // { dg-warning "is used uninitialized" }
+    return a;
+}
diff --git a/gcc/tree-ssa-uninit.cc b/gcc/tree-ssa-uninit.cc
index eae29f8..bde2399 100644
--- a/gcc/tree-ssa-uninit.cc
+++ b/gcc/tree-ssa-uninit.cc
@@ -991,14 +991,20 @@ warn_uninitialized_vars (bool wmaybe_uninit)
   auto_bb_flag ft_reachable (cfun);
 
   /* Mark blocks that are always executed when we ignore provably
-     not executed edges.  */
+     not executed and EH and abnormal edges.  */
   basic_block bb = single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun));
   while (!(bb->flags & ft_reachable))
     {
       bb->flags |= ft_reachable;
+      edge e = find_fallthru_edge (bb->succs);
+      if (e && e->flags & EDGE_EXECUTABLE)
+	{
+	  bb = e->dest;
+	  continue;
+	}
       /* Find a single executable edge.  */
       edge_iterator ei;
-      edge e, ee = NULL;
+      edge ee = NULL;
       FOR_EACH_EDGE (e, ei, bb->succs)
 	if (e->flags & EDGE_EXECUTABLE)
 	  {
-- 
2.7.4