From 844eed3364309bd20cbb7d6793a16b7c6b889ba4 Mon Sep 17 00:00:00 2001
From: Jonathan Wakely <jwakely@redhat.com>
Date: Mon, 31 Mar 2025 12:30:44 +0100
Subject: [PATCH] libstdc++: Fix -Warray-bounds warning in std::vector::resize
 [PR114945]
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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>
---
 libstdc++-v3/include/bits/vector.tcc          |  3 ++
 .../23_containers/vector/capacity/114945.cc   | 36 +++++++++++++++++++
 2 files changed, 39 insertions(+)
 create mode 100644 libstdc++-v3/testsuite/23_containers/vector/capacity/114945.cc

diff --git a/libstdc++-v3/include/bits/vector.tcc b/libstdc++-v3/include/bits/vector.tcc
index 7a92f34ec644..66d73b4cfd7e 100644
--- a/libstdc++-v3/include/bits/vector.tcc
+++ b/libstdc++-v3/include/bits/vector.tcc
@@ -768,6 +768,9 @@ _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 000000000000..daafc59d5a9d
--- /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);
+}
-- 
2.47.2