sepavloff marked an inline comment as done.
sepavloff added inline comments.
================
Comment at: llvm/include/llvm/ADT/FloatingPointMode.h:26
+/// assigned to the rounding modes must agree with the values used by
FLT_ROUNDS
+/// (C11, 5.2.4.2.2p8).
+enum class RoundingMode : int8_t {
----------------
rjmccall wrote:
> I agree that we should use one enum across LLVM and Clang. I'm not sure that
> using the `FLT_ROUNDS` values is worthwhile, especially since (1)
> `FLT_ROUNDS` doesn't specify a value for some of these (like
> `NearestTiesToAway`) and (2) some of the values it does use (e.g. for
> "indeterminable") make this actively more awkward to store. And the most
> useful thing we could do — matching the values of `FE_TONEAREST` and so on —
> isn't possible because those values are unportable. I'd rather we just pick
> arbitrary, non-ABI-stable values, like we normally would, and then make the
> places that rely on matching some external schema translate.
> (1) FLT_ROUNDS doesn't specify a value for some of these (like
> NearestTiesToAway)
In the recent C standard draft
(http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2454.pdf), there is support
of all 5 rounding modes including values returned by `FLT_ROUNDS`
(5.2.4.2.2p11), values used by `fegetround` and `fesetround`
(FE_TONEARESTFROMZERO in 7.6p13)
> (2) some of the values it does use (e.g. for "indeterminable") make this
> actively more awkward to store.
This is not a rounding mode value, it is just error indicator returned by
intrinsic functions, it does not need to be stored. Added comment about that.
> And the most useful thing we could do — matching the values of FE_TONEAREST
> and so on — isn't possible because those values are unportable.
I am working on patch that implements `fesetround` as intrinsic function. It
introduces two intrinsic functions, one is `llvm.set_rounding` (D74729 [FPEnv]
Intrinsic for setting rounding mode) and the other is `llvm.convert_rounding`
(unpublished yet). The latter translates platform-dependent values like
FE_DOWNWARD into platform independent representation, which is the same as used
by FLT_ROUNDS.
Actually the motivation for this patch was just the need to have
platform-independent representation of rounding mode that could be used in IR,
which is more or less platform-independent. The representation used by
`FLT_ROUNDS` fits these purposes because:
* it is platform-neutral,
* it is defined by standard, and
* it encodes all IEEE rounding modes.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D77379/new/
https://reviews.llvm.org/D77379
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