[PATCH] fortran: fix handling of options -ffpe-trap and -ffpe-summary [PR110957]

[Harald Anlauf <anlauf@gmx.de>]

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Dear all,

the attached simple patch fixes a mixup of error messages for -ffpe-trap
and -ffpe-summary.  While at it, I though it might be useful to accept
'none' as allowable argument to -ffpe-trap, so that traps previously set
on the command line may be cleared.  This change is also documented.

Regtested on x86_64-pc-linux-gnu.  OK for mainline?

***

The reporter also suggested to detect and handle -fno-trapping-math
when any trap is enabled.

I am not so sure that this can be required.  In gfortran, specifying
-ffpe-trap sets the FPU mask in the main and has no further effect.
Or am I missing something?

Any further opinions or insights?

Thanks,
Harald


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From 75dc455f21cea07e64b422c9994ab8879df388de Mon Sep 17 00:00:00 2001
From: Harald Anlauf <anlauf@gmx.de>
Date: Fri, 6 Oct 2023 22:21:56 +0200
Subject: [PATCH] fortran: fix handling of options -ffpe-trap and -ffpe-summary
 [PR110957]

gcc/fortran/ChangeLog:

	PR fortran/110957
	* invoke.texi: Update documentation to reflect '-ffpe-trap=none'.
	* options.cc (gfc_handle_fpe_option): Fix mixup up of error messages
	for options -ffpe-trap and -ffpe-summary.  Accept '-ffpe-trap=none'
	to clear FPU traps previously set on command line.
---
 gcc/fortran/invoke.texi | 6 ++++--
 gcc/fortran/options.cc  | 9 ++++++---
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/gcc/fortran/invoke.texi b/gcc/fortran/invoke.texi
index 38150b1e29e..10387e39501 100644
--- a/gcc/fortran/invoke.texi
+++ b/gcc/fortran/invoke.texi
@@ -1294,7 +1294,8 @@ 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
+is a (possibly empty) comma-separated list of either @samp{none} (to
+clear the set of exceptions to be trapped), or 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
@@ -1314,7 +1315,8 @@ If the option is used more than once in the command line, the lists will
 be joined: '@code{ffpe-trap=}@var{list1} @code{ffpe-trap=}@var{list2}'
 is equivalent to @code{ffpe-trap=}@var{list1},@var{list2}.

-Note that once enabled an exception cannot be disabled (no negative form).
+Note that once enabled an exception cannot be disabled (no negative form),
+except by clearing all traps by specifying @samp{none}.

 Many, if not most, floating point operations incur loss of precision
 due to rounding, and hence the @code{ffpe-trap=inexact} is likely to
diff --git a/gcc/fortran/options.cc b/gcc/fortran/options.cc
index 27311961325..2ad22478042 100644
--- a/gcc/fortran/options.cc
+++ b/gcc/fortran/options.cc
@@ -555,9 +555,12 @@ gfc_handle_fpe_option (const char *arg, bool trap)
 	pos++;

       result = 0;
-      if (!trap && strncmp ("none", arg, pos) == 0)
+      if (strncmp ("none", arg, pos) == 0)
 	{
-	  gfc_option.fpe_summary = 0;
+	  if (trap)
+	    gfc_option.fpe = 0;
+	  else
+	    gfc_option.fpe_summary = 0;
 	  arg += pos;
 	  pos = 0;
 	  continue;
@@ -586,7 +589,7 @@ gfc_handle_fpe_option (const char *arg, bool trap)
 	      break;
 	    }
 	  }
-      if (!result && !trap)
+      if (!result && trap)
 	gfc_fatal_error ("Argument to %<-ffpe-trap%> is not valid: %s", arg);
       else if (!result)
 	gfc_fatal_error ("Argument to %<-ffpe-summary%> is not valid: %s", arg);
--
2.35.3