Clarify FP exception documentation and messages

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@173944 138bc75d-0d04-0410-961f-82ee72b054a4

5 files changed, 44 insertions, 25 deletions

diff --git a/gcc/fortran/ChangeLog b/gcc/fortran/ChangeLog
index a6fffdfd4d0..5677c4c48fa 100644
--- a/gcc/fortran/ChangeLog
+++ b/gcc/fortran/ChangeLog
@@ -1,4 +1,12 @@
-2011-06-19  Tobias Burnus  <burnus@net-b.de>
+2011-05-20  Janne Blomqvist  <jb@gcc.gnu.org>
+
+        * gfortran.texi (set_fpe): Update documentation.
+        * invoke.texi (-ffpe-trap): Likewise.
+        * libgfortran.h (GFC_FPE_PRECISION): Rename to GFC_FPE_INEXACT.
+        * options.c (gfc_handle_fpe_trap_option): Handle inexact and make
+        precision an alias for it.
+
+2011-05-19  Tobias Burnus  <burnus@net-b.de>
 
 	PR fortran/18918
 	* trans-types.c (gfc_get_element_type): Handle scalar coarrays.
diff --git a/gcc/fortran/gfortran.texi b/gcc/fortran/gfortran.texi
index 995d9d8eab8..4db506c5391 100644
--- a/gcc/fortran/gfortran.texi
+++ b/gcc/fortran/gfortran.texi
@@ -2718,16 +2718,15 @@ int main (int argc, char *argv[])
 
 
 @node _gfortran_set_fpe
-@subsection @code{_gfortran_set_fpe} --- Set when a Floating Point Exception should be raised
+@subsection @code{_gfortran_set_fpe} --- Enable floating point exception traps
 @fnindex _gfortran_set_fpe
 @cindex libgfortran initialization, set_fpe
 
 @table @asis
 @item @emph{Description}:
-@code{_gfortran_set_fpe} sets the IEEE exceptions for which a
-Floating Point Exception (FPE) should be raised.  On most systems,
-this will result in a SIGFPE signal being sent and the program
-being interrupted.
+@code{_gfortran_set_fpe} enables floating point exception traps for
+the specified exceptions.  On most systems, this will result in a
+SIGFPE signal being sent and the program being aborted.
 
 @item @emph{Syntax}:
 @code{void _gfortran_set_fpe (int val)}
@@ -2738,7 +2737,7 @@ being interrupted.
 (bitwise or-ed) zero (0, default) no trapping,
 @code{GFC_FPE_INVALID} (1), @code{GFC_FPE_DENORMAL} (2),
 @code{GFC_FPE_ZERO} (4), @code{GFC_FPE_OVERFLOW} (8),
-@code{GFC_FPE_UNDERFLOW} (16), and @code{GFC_FPE_PRECISION} (32).
+@code{GFC_FPE_UNDERFLOW} (16), and @code{GFC_FPE_INEXACT} (32).
 @end multitable
 
 @item @emph{Example}:
diff --git a/gcc/fortran/invoke.texi b/gcc/fortran/invoke.texi
index ab45072efad..41fee670a6c 100644
--- a/gcc/fortran/invoke.texi
+++ b/gcc/fortran/invoke.texi
@@ -919,21 +919,31 @@ GNU Fortran compiler itself.  This option is deprecated; use
 
 @item -ffpe-trap=@var{list}
 @opindex @code{ffpe-trap=}@var{list}
-Specify a list of IEEE exceptions when a Floating Point Exception
-(FPE) should be raised.  On most systems, this will result in a SIGFPE
-signal being sent and the program being interrupted, producing a core
-file useful for debugging.  @var{list} is a (possibly empty) comma-separated
-list of the following IEEE exceptions: @samp{invalid} (invalid floating
-point operation, such as @code{SQRT(-1.0)}), @samp{zero} (division by
-zero), @samp{overflow} (overflow in a floating point operation),
-@samp{underflow} (underflow in a floating point operation),
-@samp{precision} (loss of precision during operation) and @samp{denormal}
-(operation produced a denormal value).
-
-Some of the routines in the Fortran runtime library, like
-@samp{CPU_TIME}, are likely to trigger floating point exceptions when
-@code{ffpe-trap=precision} is used. For this reason, the use of 
-@code{ffpe-trap=precision} is not recommended.
+Specify a list of floating point exception traps to enable.  On most
+systems, if a floating point exception occurs and the trap for that
+exception is enabled, a SIGFPE signal will be sent and the program
+being aborted, producing a core file useful for debugging.  @var{list}
+is a (possibly empty) comma-separated list of the following
+exceptions: @samp{invalid} (invalid floating point operation, such as
+@code{SQRT(-1.0)}), @samp{zero} (division by zero), @samp{overflow}
+(overflow in a floating point operation), @samp{underflow} (underflow
+in a floating point operation), @samp{inexact} (loss of precision
+during operation), and @samp{denormal} (operation performed on a
+denormal value).  The first five exceptions correspond to the five
+IEEE 754 exceptions, whereas the last one (@samp{denormal}) is not
+part of the IEEE 754 standard but is available on some common
+architectures such as x86.
+
+The first three exceptions (@samp{invalid}, @samp{zero}, and
+@samp{overflow}) often indicate serious errors, and unless the program
+has provisions for dealing with these exceptions, enabling traps for
+these three exceptions is probably a good idea.
+
+Many, if not most, floating point operations incur loss of precision
+due to rounding, and hence the @code{ffpe-trap=inexact} is likely to
+be uninteresting in practice.
+
+By default no exception traps are enabled.
 
 @item -fno-backtrace
 @opindex @code{fno-backtrace}
diff --git a/gcc/fortran/libgfortran.h b/gcc/fortran/libgfortran.h
index 035a32a7507..b2137bbf80f 100644
--- a/gcc/fortran/libgfortran.h
+++ b/gcc/fortran/libgfortran.h
@@ -42,7 +42,7 @@ along with GCC; see the file COPYING3.  If not see
 #define GFC_FPE_ZERO       (1<<2)
 #define GFC_FPE_OVERFLOW   (1<<3)
 #define GFC_FPE_UNDERFLOW  (1<<4)
-#define GFC_FPE_PRECISION  (1<<5)
+#define GFC_FPE_INEXACT    (1<<5)
 
 
 /* Bitmasks for the various runtime checks that can be enabled.  */
diff --git a/gcc/fortran/options.c b/gcc/fortran/options.c
index 920b95f33fe..4c59bd59eeb 100644
--- a/gcc/fortran/options.c
+++ b/gcc/fortran/options.c
@@ -492,12 +492,14 @@ static void
 gfc_handle_fpe_trap_option (const char *arg)
 {
   int result, pos = 0, n;
+  /* precision is a backwards compatibility alias for inexact.  */
   static const char * const exception[] = { "invalid", "denormal", "zero",
 					    "overflow", "underflow",
-					    "precision", NULL };
+					    "inexact", "precision", NULL };
   static const int opt_exception[] = { GFC_FPE_INVALID, GFC_FPE_DENORMAL,
 				       GFC_FPE_ZERO, GFC_FPE_OVERFLOW,
-				       GFC_FPE_UNDERFLOW, GFC_FPE_PRECISION,
+				       GFC_FPE_UNDERFLOW, GFC_FPE_INEXACT,
+				       GFC_FPE_INEXACT,
 				       0 };
  
   while (*arg)