Our documentation indicates that it is the `-frounding-math' invocation
option that controls whether we respect what the FENV_ACCESS pragma
would imply, should we implement it, regarding the floating point
environment. It is only a part of the picture however, because the
`-ftrapping-math' invocation option also affects how we handle said
environment. Clarify that in the description of both options then, as
well as the FENV_ACCESS pragma itself.
gcc/
* doc/implement-c.texi (Floating point implementation): Mention
`-fno-trapping-math' in the context of FENV_ACCESS pragma.
* doc/invoke.texi (Optimize Options): Clarify FENV_ACCESS pragma
implication in the descriptions of `-fno-trapping-math' and
`-frounding-math'.
---
Hi,
Discovered in the course of investigating RISC-V unordered comparisons,
c.f. <https://gcc.gnu.org/pipermail/gcc-patches/2022-July/597767.html>.
Maciej
---
gcc/doc/implement-c.texi | 3 ++-
gcc/doc/invoke.texi | 8 +++++++-
2 files changed, 9 insertions(+), 2 deletions(-)
gcc-doc-fenv-access-trapping.diff
Index: gcc/gcc/doc/implement-c.texi
===================================================================
--- gcc.orig/gcc/doc/implement-c.texi
+++ gcc/gcc/doc/implement-c.texi
@@ -339,7 +339,8 @@ This is subject to change.
7.6.1).}
This pragma is not implemented, but the default is to ``off'' unless
-@option{-frounding-math} is used in which case it is ``on''.
+@option{-frounding-math} is used and @option{-fno-trapping-math} is not
+in which case it is ``on''.
@item
@cite{Additional floating-point exceptions, rounding modes, environments,
Index: gcc/gcc/doc/invoke.texi
===================================================================
--- gcc.orig/gcc/doc/invoke.texi
+++ gcc/gcc/doc/invoke.texi
@@ -13513,6 +13513,11 @@ math functions.
The default is @option{-ftrapping-math}.
+Future versions of GCC may provide finer control of this setting
+using C99's @code{FENV_ACCESS} pragma. This command-line option
+will be used along with @option{-frounding-math} to specify the
+default state for @code{FENV_ACCESS}.
+
@item -frounding-math
@opindex frounding-math
Disable transformations and optimizations that assume default floating-point
@@ -13531,7 +13536,8 @@ This option is experimental and does not
disable all GCC optimizations that are affected by rounding mode.
Future versions of GCC may provide finer control of this setting
using C99's @code{FENV_ACCESS} pragma. This command-line option
-will be used to specify the default state for @code{FENV_ACCESS}.
+will be used along with @option{-ftrapping-math} to specify the
+default state for @code{FENV_ACCESS}.
@item -fsignaling-nans
@opindex fsignaling-nans
