[gcc r11-8162] PR tree-optimization/82800 - Incorrect warning on "may be used uninitialized in variadic template co

[gcc r11-8162] PR tree-optimization/82800 - Incorrect warning on "may be used uninitialized in variadic template co

[Martin Sebor]

https://gcc.gnu.org/g:af7128621e54f04b90589bb0c3e1ef271c239265

commit r11-8162-gaf7128621e54f04b90589bb0c3e1ef271c239265
Author: Martin Sebor <msebor@redhat.com>
Date:   Tue Apr 13 14:53:26 2021 -0600

    PR tree-optimization/82800 - Incorrect warning on "may be used uninitialized in variadic template code
    
    gcc/testsuite/ChangeLog:
            PR tree-optimization/82800
            * g++.dg/warn/uninit-pr82800.C: New test.

Diff:
---
 gcc/testsuite/g++.dg/warn/uninit-pr82800.C | 43 ++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/gcc/testsuite/g++.dg/warn/uninit-pr82800.C b/gcc/testsuite/g++.dg/warn/uninit-pr82800.C
new file mode 100644
index 00000000000..dc3ce5d89e3
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/uninit-pr82800.C
@@ -0,0 +1,43 @@
+/* PR 82800 - Incorrect warning on "may be used uninitialized in
+   variadic template code
+   { dg-do compile { target c++11 } }
+   { dg-options "-O2 -Wall" } */
+
+typedef __SIZE_TYPE__ size_t;
+
+extern "C" int rand ();
+
+struct Maker
+{
+  double makeConst()
+  {
+    return pick<double>(0, 0, 0, 0, 0, 0, 1);   // { dg-bogus "uninitialized" }
+  }
+
+  template<typename T, typename... Args>
+  T pick(T first, Args... args)
+  {
+    return pickGivenNum<T>(rand(), first, args...);
+  }
+
+  template<typename T>
+  T pickGivenNum(size_t num, T first)
+  {
+    if (num != 0) __builtin_abort();
+    return first;
+  }
+
+  template<typename T, typename... Args>
+  T pickGivenNum(size_t num, T first, Args... args)
+  {
+    if (num == 0) return first;
+    return pickGivenNum<T>(num - 1, args...);
+  }
+};
+
+int main ()
+{
+  Maker maker;
+  maker.makeConst();
+  maker.makeConst();
+}