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Minor optimisations in operator new(size_t, align_val_t)

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* libsupc++/new_opa.cc (operator new(size_t, align_val_t)): Use
	__is_pow2 to check for valid alignment. Avoid branching when rounding
	size to multiple of alignment.

From-SVN: r263515
This commit is contained in:
Jonathan Wakely 2018-08-13 19:54:38 +01:00 • committed by Jonathan Wakely
parent 7997ede243
commit 2383ed0269
2 changed files with 7 additions and 3 deletions
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4
libstdc++-v3/ChangeLog
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@ -1,5 +1,9 @@
2018-08-13 Jonathan Wakely <jwakely@redhat.com>
* libsupc++/new_opa.cc (operator new(size_t, align_val_t)): Use
__is_pow2 to check for valid alignment. Avoid branching when rounding
size to multiple of alignment.
* include/Makefile.am: Install <bit> and <version> for freestanding.
* include/Makefile.in: Regenerate.
* testsuite/17_intro/freestanding.cc: Check for <bit> and <version>.

6
libstdc++-v3/libsupc++/new_opa.cc
View file

@ -27,6 +27,7 @@
#include <stdlib.h>
#include <stdint.h>
#include <bits/exception_defines.h>
#include <bit>
#include "new"
#if !_GLIBCXX_HAVE_ALIGNED_ALLOC && !_GLIBCXX_HAVE__ALIGNED_MALLOC \
@ -105,7 +106,7 @@ operator new (std::size_t sz, std::align_val_t al)
/* Alignment must be a power of two. */
/* XXX This should be checked by the compiler (PR 86878). */
if (__builtin_expect (align & (align - 1), false))
if (__builtin_expect (!std::__ispow2(align), false))
_GLIBCXX_THROW_OR_ABORT(bad_alloc());
/* malloc (0) is unpredictable; avoid it. */
@ -120,8 +121,7 @@ operator new (std::size_t sz, std::align_val_t al)
align = sizeof(void*);
# endif
/* C11: the value of size shall be an integral multiple of alignment. */
if (std::size_t rem = sz & (align - 1))
sz += align - rem;
sz = (sz + align - 1) & ~(align - 1);
#endif
void *p;