new file mode 100644
@@ -0,0 +1,78 @@
+/* Macro for explicit loop unrolling.
+ Copyright (C) 2019 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <http://www.gnu.org/licenses/>. */
+
+#ifndef _LOOP_UNROLL_H
+#define _LOOP_UNROLL_H
+
+/* Loop unroll macro to be used for explicity force loop unrolling with a
+ configurable number or iterations. The idea is to make the loop unrolling
+ independent of whether compiler is able to unrolling through specific
+ optimizations options (-funroll-loops or -funroll-all-loops).
+
+ For instance, to implement strcpy with SRC being the source input and
+ DEST the destination buffer, it is expected the macro to be used in this
+ way:
+
+ #define ITERATION(index) \
+ ({ char c = *str++; *dest++ = c; c != '\0' })
+
+ while (1)
+ UNROLL_REPEAT (4, ITERATION)
+
+ The loop will be manually unrolled 4 times. Another option is to do
+ the index update after the tests:
+
+ #define ITERATION(index) \
+ ({ char c = *(str + index); *(dest + index) = c; c != '\0' })
+ #define UPDATE(n) \
+ str += n; dst += n
+
+ while (1)
+ UNROLL_REPEAT_UPDATE (4, ITERATION, UPDATE)
+
+ The loop will be manually unrolled 4 times and the SRC and DEST pointers
+ will be update only after last iteration.
+
+ Currently both macros unrolls the loop 8 times at maximum. */
+
+#define UNROLL_REPEAT_1(X) if (!X(0)) break;
+#define UNROLL_REPEAT_2(X) UNROLL_REPEAT_1(X) if (!X(1)) break;
+#define UNROLL_REPEAT_3(X) UNROLL_REPEAT_2(X) if (!X(2)) break;
+#define UNROLL_REPEAT_4(X) UNROLL_REPEAT_3(X) if (!X(3)) break;
+#define UNROLL_REPEAT_5(X) UNROLL_REPEAT_4(X) if (!X(4)) break;
+#define UNROLL_REPEAT_6(X) UNROLL_REPEAT_5(X) if (!X(5)) break;
+#define UNROLL_REPEAT_7(X) UNROLL_REPEAT_6(X) if (!X(6)) break;
+#define UNROLL_REPEAT_8(X) UNROLL_REPEAT_7(X) if (!X(7)) break;
+
+#define UNROLL_EXPAND(...) __VA_ARGS__
+
+#define UNROLL_REPEAT__(N, X) UNROLL_EXPAND(UNROLL_REPEAT_ ## N) (X)
+#define UNROLL_REPEAT_(N, X) UNROLL_REPEAT__ (N, X)
+
+#define UNROLL_REPEAT(N, X) \
+ (void) ({ \
+ UNROLL_REPEAT_(UNROLL_EXPAND(N), X); \
+ })
+
+#define UNROLL_REPEAT_UPDATE(N, X, U) \
+ (void) ({ \
+ UNROLL_REPEAT_ (UNROLL_EXPAND(N), X); \
+ UPDATE (N); \
+ })
+
+#endif
@@ -17,6 +17,7 @@
<http://www.gnu.org/licenses/>. */
#include <wchar.h>
+#include <loop_unroll.h>
#ifdef WCSCPY
@@ -27,7 +28,25 @@
wchar_t *
__wcscpy (wchar_t *dest, const wchar_t *src)
{
+#ifndef UNROLL_NTIMES
return __wmemcpy (dest, src, __wcslen (src) + 1);
+#else
+ /* Some architectures might have costly tail function call (powerpc
+ for instance) where wmemcpy call overhead for smalls sizes might
+ be costly than just unroll the main loop. */
+ wchar_t *wcp = dest;
+
+#define ITERATION(index) \
+ ({ \
+ wchar_t c = *src++; \
+ *wcp++ = c; \
+ c != L'\0'; \
+ })
+
+ while (1)
+ UNROLL_REPEAT(UNROLL_NTIMES, ITERATION);
+ return dest;
+#endif
}
#ifndef WCSCPY
weak_alias (__wcscpy, wcscpy)