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* [newlib-cygwin] bitset: avoid pessimized code when bitset size is not constant
@ 2022-06-24 5:42 Sebastian Huber
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From: Sebastian Huber @ 2022-06-24 5:42 UTC (permalink / raw)
To: newlib-cvs
https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=96c645a0b1e8c136f0d70106b8ab3d0acf621c12
commit 96c645a0b1e8c136f0d70106b8ab3d0acf621c12
Author: Ryan Libby <rlibby@FreeBSD.org>
Date: Tue Dec 3 17:43:57 2019 +0000
bitset: avoid pessimized code when bitset size is not constant
We have a couple optimizations for when the bitset is known to be just
one word. But with dynamically sized bitsets, it was actually more work
to determine the size than just to do the necessary computation. Now,
only use the optimization when the size is known to be constant.
Reviewed by: markj
Discussed with: jeff
Sponsored by: Dell EMC Isilon
Differential Revision: https://reviews.freebsd.org/D22639
Diff:
---
newlib/libc/sys/rtems/include/sys/bitset.h | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/newlib/libc/sys/rtems/include/sys/bitset.h b/newlib/libc/sys/rtems/include/sys/bitset.h
index d119c23ca..0334939c9 100644
--- a/newlib/libc/sys/rtems/include/sys/bitset.h
+++ b/newlib/libc/sys/rtems/include/sys/bitset.h
@@ -37,12 +37,19 @@
#include <sys/_types.h>
#include <machine/_bitcount.h>
+/*
+ * Whether expr is both constant and true. Result is itself constant.
+ * Used to enable optimizations for sets with a known small size.
+ */
+#define __constexpr_cond(expr) (__builtin_constant_p((expr)) && (expr))
+
#define __bitset_mask(_s, n) \
- (1L << ((__bitset_words((_s)) == 1) ? \
+ (1L << (__constexpr_cond(__bitset_words((_s)) == 1) ? \
(__size_t)(n) : ((n) % _BITSET_BITS)))
#define __bitset_word(_s, n) \
- ((__bitset_words((_s)) == 1) ? 0 : ((n) / _BITSET_BITS))
+ (__constexpr_cond(__bitset_words((_s)) == 1) ? \
+ 0 : ((n) / _BITSET_BITS))
#define BIT_CLR(_s, n, p) \
((p)->__bits[__bitset_word(_s, n)] &= ~__bitset_mask((_s), (n)))
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