From: Jonathan Wakely <jwakely@redhat.com>
To: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org
Subject: [committed] libstdc++: Disable all emergency EH pool code if obj-count == 0
Date: Fri, 14 Oct 2022 15:36:55 +0100 [thread overview]
Message-ID: <20221014143655.2512929-1-jwakely@redhat.com> (raw)
Tested x86_64-linux. Pushed to trunk.
-- >8 --
For a zero-sized static pool we can completely elide all code for the EH
pool.
We no longer need to adjust the static buffer size to ensure at least
one free_entry can be created in it, because we no longer use a static
buffer at all if obj_count == 0. If the buffer exists, obj_count >= 1
and the buffer will be much larger than sizeof(free_entry).
libstdc++-v3/ChangeLog:
* libsupc++/eh_alloc.cc [USE_POOL]: New macro.
[!USE_POOL] (__gnu_cxx::__freeres, pool): Do not define.
[_GLIBCXX_EH_POOL_STATIC] (pool::arena): Do not use std::max.
(__cxxabiv1::__cxa_allocate_exception) [!USE_POOL]: Do not use
pool.
(__cxxabiv1::__cxa_free_exception) [!USE_POOL]: Likewise.
(__cxxabiv1::__cxa_allocate_dependent_exception) [!USE_POOL]:
Likewise.
(__cxxabiv1::__cxa_free_dependent_exception) [!USE_POOL]:
Likewise.
---
libstdc++-v3/libsupc++/eh_alloc.cc | 20 +++++++++++++++++++-
1 file changed, 19 insertions(+), 1 deletion(-)
diff --git a/libstdc++-v3/libsupc++/eh_alloc.cc b/libstdc++-v3/libsupc++/eh_alloc.cc
index 81b8a1548c6..e93f14c887b 100644
--- a/libstdc++-v3/libsupc++/eh_alloc.cc
+++ b/libstdc++-v3/libsupc++/eh_alloc.cc
@@ -101,12 +101,21 @@ using namespace __cxxabiv1;
#ifdef _GLIBCXX_EH_POOL_NOBJS
# if _GLIBCXX_EH_POOL_NOBJS > MAX_OBJ_COUNT
# warning "_GLIBCXX_EH_POOL_NOBJS value is too large; ignoring it"
+# elif _GLIBCXX_EH_POOL_NOBJS < 0
+# warning "_GLIBCXX_EH_POOL_NOBJS value is negative; ignoring it"
# else
# undef EMERGENCY_OBJ_COUNT
# define EMERGENCY_OBJ_COUNT _GLIBCXX_EH_POOL_NOBJS
# endif
#endif
+#if defined _GLIBCXX_EH_POOL_STATIC && EMERGENCY_OBJ_COUNT == 0
+# define USE_POOL 0
+#else
+# define USE_POOL 1
+#endif
+
+#if USE_POOL
namespace __gnu_cxx
{
void __freeres() noexcept;
@@ -161,7 +170,7 @@ namespace
#ifdef _GLIBCXX_EH_POOL_STATIC
static constexpr std::size_t arena_size
= buffer_size_in_bytes(EMERGENCY_OBJ_COUNT, EMERGENCY_OBJ_SIZE);
- alignas(void*) char arena[std::max(arena_size, sizeof(free_entry))];
+ alignas(void*) char arena[arena_size];
#else
char *arena = nullptr;
std::size_t arena_size = 0;
@@ -374,6 +383,7 @@ namespace __gnu_cxx
#endif
}
}
+#endif // USE_POOL
extern "C" void *
__cxxabiv1::__cxa_allocate_exception(std::size_t thrown_size) noexcept
@@ -382,8 +392,10 @@ __cxxabiv1::__cxa_allocate_exception(std::size_t thrown_size) noexcept
void *ret = malloc (thrown_size);
+#if USE_POOL
if (!ret)
ret = emergency_pool.allocate (thrown_size);
+#endif
if (!ret)
std::terminate ();
@@ -398,9 +410,11 @@ extern "C" void
__cxxabiv1::__cxa_free_exception(void *vptr) noexcept
{
char *ptr = (char *) vptr - sizeof (__cxa_refcounted_exception);
+#if USE_POOL
if (emergency_pool.in_pool (ptr)) [[__unlikely__]]
emergency_pool.free (ptr);
else
+#endif
free (ptr);
}
@@ -410,8 +424,10 @@ __cxxabiv1::__cxa_allocate_dependent_exception() noexcept
{
void *ret = malloc (sizeof (__cxa_dependent_exception));
+#if USE_POOL
if (!ret)
ret = emergency_pool.allocate (sizeof (__cxa_dependent_exception));
+#endif
if (!ret)
std::terminate ();
@@ -426,8 +442,10 @@ extern "C" void
__cxxabiv1::__cxa_free_dependent_exception
(__cxa_dependent_exception *vptr) noexcept
{
+#if USE_POOL
if (emergency_pool.in_pool (vptr)) [[__unlikely__]]
emergency_pool.free (vptr);
else
+#endif
free (vptr);
}
--
2.37.3
reply other threads:[~2022-10-14 14:36 UTC|newest]
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