[PATCH] Minor optimisations in operator new(size_t, align_val_t)
Jonathan Wakely
jwakely@redhat.com
Mon Aug 13 19:00:00 GMT 2018
Thanks to Lars for the suggestions.
* 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.
Tested x86_64-linux, committed to trunk.
-------------- next part --------------
commit 766770a4f8692ef5fda2d1f987054864efb1c3a8
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Mon Aug 13 13:56:04 2018 +0100
Minor optimisations in operator new(size_t, align_val_t)
* 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.
diff --git a/libstdc++-v3/libsupc++/new_opa.cc b/libstdc++-v3/libsupc++/new_opa.cc
index aa3e5dc4ce5..abb7451fafe 100644
--- a/libstdc++-v3/libsupc++/new_opa.cc
+++ b/libstdc++-v3/libsupc++/new_opa.cc
@@ -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;
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