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Re: [PATCH] Fixes tree-loop-distribute-patterns issues
- From: Adhemerval Zanella <azanella at linux dot vnet dot ibm dot com>
- To: Roland McGrath <roland at hack dot frob dot com>
- Cc: "Carlos O'Donell" <carlos at redhat dot com>, "GNU C. Library" <libc-alpha at sourceware dot org>, Siddhesh Poyarekar <siddhesh at redhat dot com>
- Date: Thu, 20 Jun 2013 11:28:07 -0300
- Subject: Re: [PATCH] Fixes tree-loop-distribute-patterns issues
- References: <51C0AFB7 dot 1060009 at linux dot vnet dot ibm dot com> <20130618205608 dot 9CCE22C0AC at topped-with-meat dot com> <51C1BFE9 dot 4070805 at linux dot vnet dot ibm dot com> <51C1CEFC dot 9000100 at redhat dot com> <51C1FE4C dot 3020400 at linux dot vnet dot ibm dot com> <20130619221130 dot 7B91A2C10E at topped-with-meat dot com>
On 19-06-2013 19:11, Roland McGrath wrote:
>>> I'm a little worried about the fragility of the test, but if it doesn't
>>> optimize to memset, then it may not optimize the internal implementation
>>> to memset, and therefore we need not avoid the benefit of the optimization.
>>>
>>> I think this is a good approach, but we will have to see how it plays out
>>> and if it is robust enough.
>> We might make it more robust (maybe trying different loops), do you think it
>> is worth to push more tests?
> I had not contemplated this sort of configure check and I don't think it's
> what we want at all. It doesn't matter whether the compiler actually
> transforms a particular case into a call. All that matters is that the
> compiler understands
> __attribute__ ((optimize ("-fno-tree-loop-distribute-patterns"))).
> If it does, then we'll use it every place we think it might matter.
>
>
I have changed the patch so the configure now only checks for support of
the compiler flag. I also changed the names as you suggested.
---
2013-06-20 Adhemerval Zanella <azanella@linux.vnet.ibm.com>
* config.h.in (HAVE_CC_INHIBIT_LOOP_TO_LIBCALL): New define.
* configure.in (libc_cv_cc_loop_to_function): Check if compiler
accepts -fno-tree-loop-distribute-patterns.
* include/libc-symbols.h (inhibit_loop_to_libcall): New macro.
* string/memmove.c (MEMMOVE): Disable loop transformation to avoid
recursive call.
* string/memset.c (memset): Likewise.
* string/test-memmove.c (simple_memmove): Disable loop transformation
to library calls.
* string/test-memset.c (simple_memset): Likewise.
* benchtests/bench-memmove.c (simple_memmove): Likewise.
* benchtests/bench-memset.c (simple_memset): Likewise.
* configure: Regenerated.
--
diff --git a/benchtests/bench-memmove.c b/benchtests/bench-memmove.c
index dccde5d..8925606 100644
--- a/benchtests/bench-memmove.c
+++ b/benchtests/bench-memmove.c
@@ -46,6 +46,7 @@ IMPL (memmove, 1)
#endif
char *
+inhibit_loop_to_libcall
simple_memmove (char *dst, const char *src, size_t n)
{
char *ret = dst;
diff --git a/benchtests/bench-memset.c b/benchtests/bench-memset.c
index 92e34f0..ea29cf3 100644
--- a/benchtests/bench-memset.c
+++ b/benchtests/bench-memset.c
@@ -63,6 +63,7 @@ builtin_memset (char *s, int c, size_t n)
#endif
char *
+inhibit_loop_to_libcall
simple_memset (char *s, int c, size_t n)
{
char *r = s, *end = s + n;
diff --git a/config.h.in b/config.h.in
index 8c2479e..b5c6f16 100644
--- a/config.h.in
+++ b/config.h.in
@@ -69,6 +69,9 @@
/* Define if the compiler supports __builtin_memset. */
#undef HAVE_BUILTIN_MEMSET
+/* Define if compiler accepts -ftree-loop-distribute-patterns. */
+#undef HAVE_CC_INHIBIT_LOOP_TO_LIBCALL
+
/* Define if the regparm attribute shall be used for local functions
(gcc on ix86 only). */
#undef USE_REGPARMS
diff --git a/configure.in b/configure.in
index 8b11081..479751b 100644
--- a/configure.in
+++ b/configure.in
@@ -1964,6 +1964,23 @@ if test -n "$submachine"; then
fi
AC_SUBST(libc_cv_cc_submachine)
+AC_CACHE_CHECK(for -fno-tree-loop-distribute-patterns,
+libc_cv_cc_loop_to_function, [dnl
+cat > conftest.c <<EOF
+void foo (void) {}
+EOF
+libc_cv_cc_loop_to_function=no
+if AC_TRY_COMMAND([${CC-cc} $CFLAGS $CPPFLAGS -c
+ -fno-tree-loop-distribute-patterns conftest.c])
+then
+ libc_cv_cc_loop_to_function=yes
+fi
+rm -f conftest*])
+if test $libc_cv_cc_loop_to_function = yes; then
+ AC_DEFINE(HAVE_CC_INHIBIT_LOOP_TO_LIBCALL)
+fi
+AC_SUBST(libc_cv_cc_loop_to_function)
+
dnl Check whether we have the gd library available.
AC_MSG_CHECKING(for libgd)
if test "$with_gd" != "no"; then
diff --git a/include/libc-symbols.h b/include/libc-symbols.h
index f043ce0..c7155b7 100644
--- a/include/libc-symbols.h
+++ b/include/libc-symbols.h
@@ -782,4 +782,11 @@ for linking")
#define libc_ifunc_hidden_def(name) \
libc_ifunc_hidden_def1 (__GI_##name, name)
+#ifdef HAVE_CC_INHIBIT_LOOP_TO_LIBCALL
+# define inhibit_loop_to_libcall \
+ __attribute__ ((__optimize__ ("-fno-tree-loop-distribute-patterns")))
+#else
+# define inhibit_loop_to_libcall
+#endif
+
#endif /* libc-symbols.h */
diff --git a/string/memmove.c b/string/memmove.c
index 9dcd2f1..ec61e28 100644
--- a/string/memmove.c
+++ b/string/memmove.c
@@ -41,6 +41,7 @@
#endif
rettype
+inhibit_loop_to_libcall
MEMMOVE (a1, a2, len)
a1const void *a1;
a2const void *a2;
diff --git a/string/memset.c b/string/memset.c
index 868be53..74b5409 100644
--- a/string/memset.c
+++ b/string/memset.c
@@ -21,6 +21,7 @@
#undef memset
void *
+inhibit_loop_to_libcall
memset (dstpp, c, len)
void *dstpp;
int c;
diff --git a/string/test-memmove.c b/string/test-memmove.c
index 4ec55b2..94576a2 100644
--- a/string/test-memmove.c
+++ b/string/test-memmove.c
@@ -47,6 +47,7 @@ IMPL (memmove, 1)
#endif
char *
+inhibit_loop_to_libcall
simple_memmove (char *dst, const char *src, size_t n)
{
char *ret = dst;
diff --git a/string/test-memset.c b/string/test-memset.c
index 9981fce..72a390e 100644
--- a/string/test-memset.c
+++ b/string/test-memset.c
@@ -64,6 +64,7 @@ builtin_memset (char *s, int c, size_t n)
#endif
char *
+inhibit_loop_to_libcall
simple_memset (char *s, int c, size_t n)
{
char *r = s, *end = s + n;