From 361d230fd7800a7e749aba8ed020f54f5c26d504 Mon Sep 17 00:00:00 2001
From: Jonathan Wakely <jwakely@redhat.com>
Date: Thu, 26 Sep 2024 16:55:07 +0100
Subject: [PATCH] libstdc++: Enable _GLIBCXX_ASSERTIONS by default for -O0
[PR112808]
Too many users don't know about -D_GLIBCXX_ASSERTIONS and so are missing
valuable checks for C++ standard library preconditions. This change
enables libstdc++ assertions by default when compiling with -O0 so that
we diagnose more bugs by default.
When users enable optimization we don't add the assertions by default
(because they have non-zero overhead) so they still need to enable them
manually.
For users who really don't want the assertions even in unoptimized
builds, defining _GLIBCXX_NO_ASSERTIONS will prevent them from being
enabled automatically.
libstdc++-v3/ChangeLog:
PR libstdc++/112808
* doc/xml/manual/using.xml (_GLIBCXX_ASSERTIONS): Document
implicit definition for -O0 compilation.
(_GLIBCXX_NO_ASSERTIONS): Document.
* doc/html/manual/using_macros.html: Regenerate.
* include/bits/c++config [!__OPTIMIZE__] (_GLIBCXX_ASSERTIONS):
Define for unoptimized builds.
---
libstdc++-v3/doc/html/manual/using_macros.html | 12 +++++++++---
libstdc++-v3/doc/xml/manual/using.xml | 16 +++++++++++++---
libstdc++-v3/include/bits/c++config | 9 +++++++--
3 files changed, 29 insertions(+), 8 deletions(-)
diff --git a/libstdc++-v3/doc/html/manual/using_macros.html b/libstdc++-v3/doc/html/manual/using_macros.html
index 67623b5e2aff..c1406ec76f77 100644
--- a/libstdc++-v3/doc/html/manual/using_macros.html
+++ b/libstdc++-v3/doc/html/manual/using_macros.html
@@ -82,9 +82,15 @@
This is described in more detail in
<a class="link" href="ext_compile_checks.html" title="Chapter 16. Compile Time Checks">Compile Time Checks</a>.
</p></dd><dt><span class="term"><code class="code">_GLIBCXX_ASSERTIONS</code></span></dt><dd><p>
- Undefined by default. When defined, enables extra error checking in
- the form of precondition assertions, such as bounds checking in
- strings and null pointer checks when dereferencing smart pointers.
+ Defined by default when compiling with no optimization, undefined
+ by default when compiling with optimization.
+ When defined, enables extra error checking in the form of
+ precondition assertions, such as bounds checking in strings
+ and null pointer checks when dereferencing smart pointers.
+ </p></dd><dt><span class="term"><code class="code">_GLIBCXX_NO_ASSERTIONS</code></span></dt><dd><p>
+ Undefined by default. When defined, prevents the implicit
+ definition of <code class="code">_GLIBCXX_ASSERTIONS</code> when compiling
+ with no optimization.
</p></dd><dt><span class="term"><code class="code">_GLIBCXX_DEBUG</code></span></dt><dd><p>
Undefined by default. When defined, compiles user code using
the <a class="link" href="debug_mode.html" title="Chapter 17. Debug Mode">debug mode</a>.
diff --git a/libstdc++-v3/doc/xml/manual/using.xml b/libstdc++-v3/doc/xml/manual/using.xml
index 89119f6fb2db..7ca3a3f4b4c0 100644
--- a/libstdc++-v3/doc/xml/manual/using.xml
+++ b/libstdc++-v3/doc/xml/manual/using.xml
@@ -1247,9 +1247,19 @@ g++ -Winvalid-pch -I. -include stdc++.h -H -g -O2 hello.cc -o test.exe
<varlistentry><term><code>_GLIBCXX_ASSERTIONS</code></term>
<listitem>
<para>
- Undefined by default. When defined, enables extra error checking in
- the form of precondition assertions, such as bounds checking in
- strings and null pointer checks when dereferencing smart pointers.
+ Defined by default when compiling with no optimization, undefined
+ by default when compiling with optimization.
+ When defined, enables extra error checking in the form of
+ precondition assertions, such as bounds checking in strings
+ and null pointer checks when dereferencing smart pointers.
+ </para>
+ </listitem></varlistentry>
+ <varlistentry><term><code>_GLIBCXX_NO_ASSERTIONS</code></term>
+ <listitem>
+ <para>
+ Undefined by default. When defined, prevents the implicit
+ definition of <code>_GLIBCXX_ASSERTIONS</code> when compiling
+ with no optimization.
</para>
</listitem></varlistentry>
<varlistentry><term><code>_GLIBCXX_DEBUG</code></term>
diff --git a/libstdc++-v3/include/bits/c++config b/libstdc++-v3/include/bits/c++config
index 29d795f687c6..b87a3527f24b 100644
--- a/libstdc++-v3/include/bits/c++config
+++ b/libstdc++-v3/include/bits/c++config
@@ -586,9 +586,14 @@ namespace std
#pragma GCC visibility pop
}
+#ifndef _GLIBCXX_ASSERTIONS
+# if defined(_GLIBCXX_DEBUG)
// Debug Mode implies checking assertions.
-#if defined(_GLIBCXX_DEBUG) && !defined(_GLIBCXX_ASSERTIONS)
-# define _GLIBCXX_ASSERTIONS 1
+# define _GLIBCXX_ASSERTIONS 1
+# elif ! defined(__OPTIMIZE__) && ! defined(_GLIBCXX_NO_ASSERTIONS)
+// Enable assertions for unoptimized builds.
+# define _GLIBCXX_ASSERTIONS 1
+# endif
#endif
// Disable std::string explicit instantiation declarations in order to assert.
--
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