From: Joseph Myers <joseph@codesourcery.com>
To: Tejas Joshi <tejasjoshi9673@gmail.com>
Cc: <gcc@gcc.gnu.org>, Martin Jambor <mjambor@suse.cz>, <hubicka@ucw.cz>
Subject: Re: [GSoC-19] Expanding fromfp variants on AArch64
Date: Mon, 19 Aug 2019 14:43:00 -0000 [thread overview]
Message-ID: <alpine.DEB.2.21.1908191430540.23785@digraph.polyomino.org.uk> (raw)
In-Reply-To: <CACMrGjBWoU3Ao8sTCiBpNQqGNSO5c6Ezq7goqsGXu-EXiySZzw@mail.gmail.com>
On Mon, 19 Aug 2019, Tejas Joshi wrote:
> How can I add a target hook to specify the FP_INT_* values from libm ?
See target.def.
You'll need a GCC-specific enum (GCC_FP_INT_*, say) that GCC uses
internally, and a hook that maps between that and FP_INT_*. I'm guessing
that for the likely uses, maybe the hook should map from FP_INT_* to
GCC_FP_INT_* (so it gets used on constant arguments to the built-in
function to say which rounding direction they are in GCC's internal enum).
It will need to be able to return that a constant doesn't map to a known
rounding mode (not an error, just means that call can't be expanded inline
or optimized to a constant).
Then the relevant macro giving the default for glibc systems should be
defined in config/gnu-user.h (see how it defines e.g.
TARGET_LIBC_HAS_FUNCTION).
> Also as this includes rounding to integers, does it involve any RTL
> related complications that we have encountered in FADD ?
The new RTL would effectively be variants of the fix_trunc and
fixuns_trunc patterns, which can use (fix) and (unsigned_fix) RTL; the new
variants would take an argument in a floating-point mode, returning one in
an integer mode - but with extra information involved about the number of
bits, rounding direction, handling of "inexact".
fix_trunc and fixuns_trunc / (fix) and (unsigned_fix) always use
FP_INT_TOWARDZERO, always use the width of the mode and have unspecified
"inexact" handling for non-integer in-range values (they correspond to C
casts) so are not themselves suitable for implementing the new built-in
functions (but the particular instructions those patterns expand to are
likely to be suitable for certain arguments to certain of the new built-in
functions).
--
Joseph S. Myers
joseph@codesourcery.com
prev parent reply other threads:[~2019-08-19 14:43 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-19 11:01 Tejas Joshi
2019-08-19 14:43 ` Joseph Myers [this message]
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