Added debug of branch prediction / --enable-debug-prediction configure

option (patch from Patrick Pélissier, with some changes).

git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@9141 280ebfd0-de03-0410-8827-d642c229c3f4

2 files changed, 89 insertions, 4 deletions

diff --git a/src/exceptions.c b/src/exceptions.c
index 912702eef..5dafa2c62 100644
--- a/src/exceptions.c
+++ b/src/exceptions.c
@@ -1,4 +1,4 @@
-/* Exception flags and utilities.
+/* Exception flags and utilities. Constructors and destructors (debug).
 
 Copyright 2001-2014 Free Software Foundation, Inc.
 Contributed by the AriC and Caramel projects, INRIA.
@@ -413,3 +413,46 @@ mpfr_overflow (mpfr_ptr x, mpfr_rnd_t rnd_mode, int sign)
   __gmpfr_flags |= MPFR_FLAGS_INEXACT | MPFR_FLAGS_OVERFLOW;
   return sign > 0 ? inex : -inex;
 }
+
+/**************************************************************************/
+
+/* Code related to constructors and destructors (for debugging) should
+   be put here. The reason is that such code must be in an object file
+   that will be kept by the linker for symbol resolution, and symbols
+   __gmpfr_emin and __gmpfr_emax from this file will be used by every
+   program calling a MPFR math function (where rounding is involved). */
+
+#if defined MPFR_DEBUG_PREDICTION
+
+/* Print prediction statistics at the end of a program.
+ *
+ * Code to debug branch prediction, based on Ulrich Drepper's paper
+ * "What Every Programmer Should Know About Memory":
+ *   http://people.freebsd.org/~lstewart/articles/cpumemory.pdf
+ */
+
+extern long int __start_predict_data;
+extern long int __stop_predict_data;
+extern long int __start_predict_line;
+extern const char *__start_predict_file;
+
+static void __attribute__ ((destructor))
+predprint (void)
+{
+  long int *s = &__start_predict_data;
+  long int *e = &__stop_predict_data;
+  long int *sl = &__start_predict_line;
+  const char **sf = &__start_predict_file;
+
+  while (s < e)
+    {
+      printf("%s:%ld: incorrect=%ld, correct=%ld%s\n",
+             *sf, *sl, s[0], s[1],
+             s[0] > s[1] ? " <==== WARNING" : "");
+      ++sl;
+      ++sf;
+      s += 2;
+    }
+}
+
+#endif
diff --git a/src/mpfr-impl.h b/src/mpfr-impl.h
index a56754b99..91f53ca74 100644
--- a/src/mpfr-impl.h
+++ b/src/mpfr-impl.h
@@ -1047,12 +1047,54 @@ typedef union { mp_size_t s; mp_limb_t l; } mpfr_size_limb_t;
 /* Theses macros help the compiler to determine if a test is
    likely or unlikely. The !! is necessary in case x is larger
    than a long. */
-#if __MPFR_GNUC(3,0) || __MPFR_ICC(8,1,0)
-# define MPFR_LIKELY(x) (__builtin_expect(!!(x),1))
-# define MPFR_UNLIKELY(x) (__builtin_expect(!!(x),0))
+#if defined MPFR_DEBUG_PREDICTION && __MPFR_GNUC(3,0)
+
+/* Code to debug branch prediction, based on Ulrich Drepper's paper
+ * "What Every Programmer Should Know About Memory":
+ *   http://people.freebsd.org/~lstewart/articles/cpumemory.pdf
+ */
+asm (".section predict_data, \"aw\"; .previous\n"
+     ".section predict_line, \"a\"; .previous\n"
+     ".section predict_file, \"a\"; .previous");
+# if defined __x86_64__
+#  define MPFR_DEBUGPRED__(e,E)                                         \
+  ({ long int _e = !!(e);                                               \
+    asm volatile (".pushsection predict_data\n"                         \
+                  "..predictcnt%=: .quad 0; .quad 0\n"                  \
+                  ".section predict_line; .quad %c1\n"                  \
+                  ".section predict_file; .quad %c2; .popsection\n"     \
+                  "addq $1,..predictcnt%=(,%0,8)"                       \
+                  : : "r" (_e == E), "i" (__LINE__), "i" (__FILE__));   \
+    __builtin_expect (_e, E);                                           \
+  })
+# elif defined __i386__
+#  define MPFR_DEBUGPRED__(e,E)                                         \
+  ({ long int _e = !!(e);                                               \
+    asm volatile (".pushsection predict_data\n"                         \
+                  "..predictcnt%=: .long 0; .long 0\n"                  \
+                  ".section predict_line; .long %c1\n"                  \
+                  ".section predict_file; .long %c2; .popsection\n"     \
+                  "incl ..predictcnt%=(,%0,4)"                          \
+                  : : "r" (_e == E), "i" (__LINE__), "i" (__FILE__));   \
+    __builtin_expect (_e, E);                                           \
+  })
+# else
+#  error "MPFR_DEBUGPRED__ definition missing"
+# endif
+
+# define MPFR_LIKELY(x) MPFR_DEBUGPRED__ ((x), 1)
+# define MPFR_UNLIKELY(x) MPFR_DEBUGPRED__ ((x), 0)
+
+#elif __MPFR_GNUC(3,0) || __MPFR_ICC(8,1,0)
+
+# define MPFR_LIKELY(x) (__builtin_expect(!!(x), 1))
+# define MPFR_UNLIKELY(x) (__builtin_expect(!!(x), 0))
+
 #else
+
 # define MPFR_LIKELY(x) (x)
 # define MPFR_UNLIKELY(x) (x)
+
 #endif
 
 /* Declare that some variable is initialized before being used (without a