PR tree-optimization/83239 - False positive from -Wstringop-overflow

PR tree-optimization/83239 - False positive from -Wstringop-overflow
on simple std::vector code

libstdc++/CHangeLog:
	* include/bits/vector.tcc (vector::_M_default_append): Assert
        invariant to generate better code.

gcc/testsuite/ChangeLog:
	* g++.dg/pr83239.C: New test case.

From-SVN: r255753

2 files changed, 61 insertions, 0 deletions

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 49c26ac..f16a187 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2017-12-16  Martin Sebor  <msebor@redhat.com>
+
+	PR tree-optimization/83239
+	* g++.dg/pr83239.C: New test case.
+
 2017-12-16  Sebastian Peryt  <sebastian.peryt@intel.com>
 
 	PR testsuite/82767
diff --git a/gcc/testsuite/g++.dg/pr83239.C b/gcc/testsuite/g++.dg/pr83239.C
new file mode 100644
index 0000000..b0f31be
--- /dev/null
+++ b/gcc/testsuite/g++.dg/pr83239.C
@@ -0,0 +1,56 @@
+// PR tree-optimization/83239 - False positive from -Wstringop-overflow
+// on simple std::vector code
+// { dg-do compile }
+// { dg-options "-O3 -Wall -fdump-tree-optimized"  }
+
+#include <vector>
+
+// Verify no warnings are issued.
+
+template <class T>
+void test_loop ()
+{
+  std::vector<T> a;
+
+  int num = 2;
+
+  while (num > 0)
+    {
+      const typename std::vector<T>::size_type sz = a.size ();
+
+      if (sz < 3)
+	a.assign (1, 0);
+      else
+	a.resize (sz - 2);
+
+      --num;
+    }
+}
+
+// Verify no warnings are issued here either.
+
+template <class T>
+void test_if (std::vector<T> &a, int num)
+{
+  if (num > 0)
+    {
+      const typename std::vector<T>::size_type sz = a.size ();
+
+      if (sz < 3)
+	a.assign (1, 0);
+      else
+	a.resize (sz - 2);
+    }
+}
+
+// Instantiate each function on a different type to force both
+// to be fully inlined.  Instantiating both on the same type
+// causes the inlining heuristics to outline _M_default_append
+// which, in turn, masks the warning.
+template void test_loop<int>();
+template void test_if<long>(std::vector<long>&, int);
+
+// Verify that std::vector<T>::_M_default_append() has been inlined
+// (the absence of warnings depends on it).
+// { dg-final { scan-tree-dump-not "_ZNSt6vectorIiSaIiEE17_M_default_appendEm"  optimized } }
+// { dg-final { scan-tree-dump-not "_ZNSt6vectorIPvSaIS0_EE17_M_default_appendEm" optimized } }