From: Jonathan Wakely <jwakely@redhat.com>
Date: Mon, 31 Mar 2025 11:30:44 +0000 (+0100)
Subject: libstdc++: Fix -Warray-bounds warning in std::vector::resize [PR114945]
X-Git-Tag: releases/gcc-14.3.0~292
X-Git-Url: http://git.ipfire.org/gitweb/gitweb.cgi?a=commitdiff_plain;h=6b11aed73f6601de32082a4519022d4de1ce8a8f;p=thirdparty%2Fgcc.git

libstdc++: Fix -Warray-bounds warning in std::vector::resize [PR114945]

This is yet another false positive warning fix. This time the compiler
can't prove that when the vector has sufficient excess capacity to
append new elements, the pointer to the existing storage is not null.

libstdc++-v3/ChangeLog:

	PR libstdc++/114945
	* include/bits/vector.tcc (vector::_M_default_append): Add
	unreachable condition so the compiler knows that _M_finish is
	not null.
	* testsuite/23_containers/vector/capacity/114945.cc: New test.

Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>

(cherry picked from commit 844eed3364309bd20cbb7d6793a16b7c6b889ba4)
---

diff --git a/libstdc++-v3/include/bits/vector.tcc b/libstdc++-v3/include/bits/vector.tcc
index 0458d560075..0bd1ae41102 100644
--- a/libstdc++-v3/include/bits/vector.tcc
+++ b/libstdc++-v3/include/bits/vector.tcc
@@ -816,6 +816,9 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 
 	  if (__navail >= __n)
 	    {
+	      if (!this->_M_impl._M_finish)
+		__builtin_unreachable();
+
 	      _GLIBCXX_ASAN_ANNOTATE_GROW(__n);
 	      this->_M_impl._M_finish =
 		std::__uninitialized_default_n_a(this->_M_impl._M_finish,
diff --git a/libstdc++-v3/testsuite/23_containers/vector/capacity/114945.cc b/libstdc++-v3/testsuite/23_containers/vector/capacity/114945.cc
new file mode 100644
index 00000000000..daafc59d5a9
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/vector/capacity/114945.cc
@@ -0,0 +1,36 @@
+// { dg-options "-O2 -Werror=stringop-overflow -Werror=array-bounds" }
+// { dg-do compile { target c++11 } }
+
+// Bug libstdc++/114945
+// Sporadic std::vector::resize() -Wstringop-overflow or -Warray-bounds warning
+
+#include <stdint.h>
+#include <vector>
+template <typename a> struct b {
+  void resize(std::size_t c) { d.resize(c); }
+  template <typename e> void f(a, e);
+  std::vector<char> d;
+};
+#include <regex>
+std::regex g;
+uint64_t h;
+uint32_t i;
+struct s {
+  enum class j : size_t;
+  void k();
+  using l = b<j>;
+  std::vector<l> m;
+};
+enum class s::j : size_t { n };
+void o() { g = ""; }
+void s::k() {
+  l p;
+  auto q = uint32_t(), r = uint32_t();
+  if (h)
+    r = i;
+  b<size_t> t;
+  if (q || r)
+    p.f(j::n, 5);
+  t.resize(4);
+  m.push_back(p);
+}