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Support C++17 over-aligned allocation

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Summary:
Add support for C++17 over-aligned allocation:
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0035r4.html

Supporting all 10 operators means we avoid thunking thru libstdc++-v3/libsupc++ and just call jemalloc directly.

It's also worth noting that there is now an aligned *and sized* operator delete:
```
void operator delete(void* ptr, std::size_t size, std::align_val_t al) noexcept;
```

If JeMalloc did not provide this, the default implementation would ignore the size parameter entirely:
https://github.com/gcc-mirror/gcc/blob/master/libstdc%2B%2B-v3/libsupc%2B%2B/del_opsa.cc#L30-L33

(I must also update ax_cxx_compile_stdcxx.m4 to a newer version with C++17 support.)

Test Plan:
Wrote a simple test that allocates and then deletes an over-aligned type:
```
struct alignas(32) Foo {};
Foo *f;

int main()
{
  f = new Foo;
  delete f;
}
```

Before this change, both new and delete go thru PLT, and we end up calling regular old free:
```
(gdb) disassemble
Dump of assembler code for function main():
...
   0x00000000004029b7 <+55>:    call   0x4022d0 <_ZnwmSt11align_val_t@plt>
...
   0x00000000004029d5 <+85>:    call   0x4022e0 <_ZdlPvmSt11align_val_t@plt>
...
(gdb) s
free (ptr=0x7ffff6408020) at /home/engshare/third-party2/jemalloc/master/src/jemalloc.git-trunk/src/jemalloc.c:2842
2842            if (!free_fastpath(ptr, 0, false)) {
```

After this change, we directly call new/delete and ultimately call sdallocx:
```
(gdb) disassemble
Dump of assembler code for function main():
...
   0x0000000000402b77 <+55>:    call   0x496ca0 <operator new(unsigned long, std::align_val_t)>
...
   0x0000000000402b95 <+85>:    call   0x496e60 <operator delete(void*, unsigned long, std::align_val_t)>
...
(gdb) s
116             je_sdallocx_noflags(ptr, size);
```
This commit is contained in:
Mark Santaniello 2019-10-26 23:28:42 -07:00 • committed by Qi Wang
parent 9a3c738009
commit 8b2c2a596d
4 changed files with 536 additions and 42 deletions
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121
src/jemalloc_cpp.cpp
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@ -39,6 +39,20 @@ void operator delete(void *ptr, std::size_t size) noexcept;
void operator delete[](void *ptr, std::size_t size) noexcept;
#endif
#if __cpp_aligned_new >= 201606
/* C++17's over-aligned operators. */
void *operator new(std::size_t size, std::align_val_t);
void *operator new(std::size_t size, std::align_val_t, const std::nothrow_t &) noexcept;
void *operator new[](std::size_t size, std::align_val_t);
void *operator new[](std::size_t size, std::align_val_t, const std::nothrow_t &) noexcept;
void operator delete(void* ptr, std::align_val_t) noexcept;
void operator delete(void* ptr, std::align_val_t, const std::nothrow_t &) noexcept;
void operator delete(void* ptr, std::size_t size, std::align_val_t al) noexcept;
void operator delete[](void* ptr, std::align_val_t) noexcept;
void operator delete[](void* ptr, std::align_val_t, const std::nothrow_t &) noexcept;
void operator delete[](void* ptr, std::size_t size, std::align_val_t al) noexcept;
#endif
JEMALLOC_NOINLINE
static void *
handleOOM(std::size_t size, bool nothrow) {
@ -76,12 +90,46 @@ JEMALLOC_ALWAYS_INLINE
void *
newImpl(std::size_t size) noexcept(IsNoExcept) {
void *ptr = je_malloc(size);
if (likely(ptr != nullptr))
if (likely(ptr != nullptr)) {
return ptr;
}
return handleOOM(size, IsNoExcept);
}
template <bool IsNoExcept>
JEMALLOC_ALWAYS_INLINE
void *
alignedNewImpl(std::size_t size, std::align_val_t alignment) noexcept(IsNoExcept) {
void *ptr = je_aligned_alloc(static_cast<std::size_t>(alignment), size);
if (likely(ptr != nullptr)) {
return ptr;
}
return handleOOM(size, IsNoExcept);
}
JEMALLOC_ALWAYS_INLINE
void
sizedDeleteImpl(void* ptr, std::size_t size) noexcept {
if (unlikely(ptr == nullptr)) {
return;
}
je_sdallocx_noflags(ptr, size);
}
JEMALLOC_ALWAYS_INLINE
void
alignedSizedDeleteImpl(void* ptr, std::size_t size, std::align_val_t alignment) noexcept {
if (config_debug) {
assert(((size_t)alignment & ((size_t)alignment - 1)) == 0);
}
if (unlikely(ptr == nullptr)) {
return;
}
je_sdallocx(ptr, size, MALLOCX_ALIGN(alignment));
}
void *
operator new(std::size_t size) {
return newImpl<false>(size);
@ -102,6 +150,30 @@ operator new[](std::size_t size, const std::nothrow_t &) noexcept {
return newImpl<true>(size);
}
#if __cpp_aligned_new >= 201606
void *
operator new(std::size_t size, std::align_val_t alignment) {
return alignedNewImpl<false>(size, alignment);
}
void *
operator new(std::size_t size, std::align_val_t alignment, const std::nothrow_t &) noexcept {
return alignedNewImpl<true>(size, alignment);
}
void *
operator new[](std::size_t size, std::align_val_t alignment) {
return alignedNewImpl<false>(size, alignment);
}
void *
operator new[](std::size_t size, std::align_val_t alignment, const std::nothrow_t &) noexcept {
return alignedNewImpl<true>(size, alignment);
}
#endif // __cpp_aligned_new
void
operator delete(void *ptr) noexcept {
je_free(ptr);
@ -125,17 +197,46 @@ void operator delete[](void *ptr, const std::nothrow_t &) noexcept {
void
operator delete(void *ptr, std::size_t size) noexcept {
if (unlikely(ptr == nullptr)) {
return;
}
je_sdallocx_noflags(ptr, size);
sizedDeleteImpl(ptr, size);
}
void operator delete[](void *ptr, std::size_t size) noexcept {
if (unlikely(ptr == nullptr)) {
return;
}
je_sdallocx_noflags(ptr, size);
void
operator delete[](void *ptr, std::size_t size) noexcept {
sizedDeleteImpl(ptr, size);
}
#endif // __cpp_sized_deallocation
#if __cpp_aligned_new >= 201606
void
operator delete(void* ptr, std::align_val_t) noexcept {
je_free(ptr);
}
void
operator delete(void* ptr, std::align_val_t, const std::nothrow_t&) noexcept {
je_free(ptr);
}
void
operator delete[](void* ptr, std::align_val_t) noexcept {
je_free(ptr);
}
void
operator delete[](void* ptr, std::align_val_t, const std::nothrow_t&) noexcept {
je_free(ptr);
}
void
operator delete(void* ptr, std::size_t size, std::align_val_t alignment) noexcept {
alignedSizedDeleteImpl(ptr, size, alignment);
}
void
operator delete[](void* ptr, std::size_t size, std::align_val_t alignment) noexcept {
alignedSizedDeleteImpl(ptr, size, alignment);
}
#endif // __cpp_aligned_new