[PATCH] Bump minimum MPFR version to 3.1.0

[Janne Blomqvist <blomqvist dot janne at gmail dot com>]

Bump the minimum MPFR version to 3.1.0, released 2011-10-03. With this
requirement one can still build GCC with the operating system provided
MPFR on old but still supported operating systems like SLES 12 (MPFR
3.1.2) or RHEL/CentOS 7.x (MPFR 3.1.1).

This allows removing some code in the Fortran frontend, as well as
fixing PR 91828.

ChangeLog:

2019-11-09  Janne Blomqvist  <jb@gcc.gnu.org>

	PR fortran/91828
	* configure.ac: Bump minimum MPFR to 3.1.0, recommended to 3.1.6+.
	* configure: Regenerated.

gcc/ChangeLog:

2019-11-09  Janne Blomqvist  <jb@gcc.gnu.org>

	PR fortran/91828
	* doc/install.texi: Document that the minimum MPFR version is
	3.1.0.

gcc/fortran/ChangeLog:

2019-11-09  Janne Blomqvist  <jb@gcc.gnu.org>

	PR fortran/91828
	* simplify.c (gfc_simplify_fraction): Remove fallback path for
	MPFR < 3.1.0.
---
 configure.ac           |  6 +++---
 gcc/doc/install.texi   |  2 +-
 gcc/fortran/simplify.c | 37 -------------------------------------
 3 files changed, 4 insertions(+), 41 deletions(-)

diff --git a/configure.ac b/configure.ac
index b8ce2ad20b9..d63a8bae940 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1601,12 +1601,12 @@ if test -d ${srcdir}/gcc && test "x$have_gmp" = xno; then
     AC_MSG_CHECKING([for the correct version of mpfr.h])
     AC_TRY_COMPILE([#include <gmp.h>
     #include <mpfr.h>],[
-    #if MPFR_VERSION < MPFR_VERSION_NUM(2,4,0)
+    #if MPFR_VERSION < MPFR_VERSION_NUM(3,1,0)
     choke me
     #endif
     ], [AC_TRY_COMPILE([#include <gmp.h>
     #include <mpfr.h>],[
-    #if MPFR_VERSION < MPFR_VERSION_NUM(2,4,2)
+    #if MPFR_VERSION < MPFR_VERSION_NUM(3,1,6)
     choke me
     #endif
     ], [AC_MSG_RESULT([yes])], [AC_MSG_RESULT([buggy but acceptable])])],
@@ -1661,7 +1661,7 @@ if test -d ${srcdir}/gcc && test "x$have_gmp" = xno; then
 # The library versions listed in the error message below should match
 # the HARD-minimums enforced above.
   if test x$have_gmp != xyes; then
-    AC_MSG_ERROR([Building GCC requires GMP 4.2+, MPFR 2.4.0+ and MPC 0.8.0+.
+    AC_MSG_ERROR([Building GCC requires GMP 4.2+, MPFR 3.1.0+ and MPC 0.8.0+.
 Try the --with-gmp, --with-mpfr and/or --with-mpc options to specify
 their locations.  Source code for these libraries can be found at
 their respective hosting sites as well as at
diff --git a/gcc/doc/install.texi b/gcc/doc/install.texi
index 2cb8a342a2c..93b01ff7971 100644
--- a/gcc/doc/install.texi
+++ b/gcc/doc/install.texi
@@ -384,7 +384,7 @@ and @option{--with-gmp-include}.
 The in-tree build is only supported with the GMP version that
 download_prerequisites installs.
 
-@item MPFR Library version 2.4.2 (or later)
+@item MPFR Library version 3.1.0 (or later)
 
 Necessary to build GCC@.  It can be downloaded from
 @uref{https://www.mpfr.org}.  If an MPFR source distribution is found
diff --git a/gcc/fortran/simplify.c b/gcc/fortran/simplify.c
index 2eb1943c3ee..0461d31cd88 100644
--- a/gcc/fortran/simplify.c
+++ b/gcc/fortran/simplify.c
@@ -3076,12 +3076,7 @@ gfc_expr *
 gfc_simplify_fraction (gfc_expr *x)
 {
   gfc_expr *result;
-
-#if MPFR_VERSION < MPFR_VERSION_NUM(3,1,0)
-  mpfr_t absv, exp, pow2;
-#else
   mpfr_exp_t e;
-#endif
 
   if (x->expr_type != EXPR_CONSTANT)
     return NULL;
@@ -3095,41 +3090,9 @@ gfc_simplify_fraction (gfc_expr *x)
       return result;
     }
 
-#if MPFR_VERSION < MPFR_VERSION_NUM(3,1,0)
-
-  /* MPFR versions before 3.1.0 do not include mpfr_frexp.
-     TODO: remove the kludge when MPFR 3.1.0 or newer will be required */
-
-  if (mpfr_sgn (x->value.real) == 0)
-    {
-      mpfr_set (result->value.real, x->value.real, GFC_RND_MODE);
-      return result;
-    }
-
-  gfc_set_model_kind (x->ts.kind);
-  mpfr_init (exp);
-  mpfr_init (absv);
-  mpfr_init (pow2);
-
-  mpfr_abs (absv, x->value.real, GFC_RND_MODE);
-  mpfr_log2 (exp, absv, GFC_RND_MODE);
-
-  mpfr_trunc (exp, exp);
-  mpfr_add_ui (exp, exp, 1, GFC_RND_MODE);
-
-  mpfr_ui_pow (pow2, 2, exp, GFC_RND_MODE);
-
-  mpfr_div (result->value.real, x->value.real, pow2, GFC_RND_MODE);
-
-  mpfr_clears (exp, absv, pow2, NULL);
-
-#else
-
   /* mpfr_frexp() correctly handles zeros and NaNs.  */
   mpfr_frexp (&e, result->value.real, x->value.real, GFC_RND_MODE);
 
-#endif
-
   return range_check (result, "FRACTION");
 }
 
-- 
2.17.1