ABataev added inline comments.
================
Comment at: clang/lib/Sema/SemaOpenMP.cpp:1594
+ !Context.getTargetInfo().hasFloat128Type() &&
+ Context.getTargetInfo().getLongDoubleWidth() != 128) ||
(Ty->isIntegerType() && Context.getTypeSize(Ty) == 128 &&
----------------
jdenny wrote:
> ABataev wrote:
> > MaskRay wrote:
> > > ABataev wrote:
> > > > jdenny wrote:
> > > > > ABataev wrote:
> > > > > > jdenny wrote:
> > > > > > > ABataev wrote:
> > > > > > > > jdenny wrote:
> > > > > > > > > ABataev wrote:
> > > > > > > > > > jdenny wrote:
> > > > > > > > > > > ABataev wrote:
> > > > > > > > > > > > jdenny wrote:
> > > > > > > > > > > > > ABataev wrote:
> > > > > > > > > > > > > > Hmm, this look strange, at least. Seems to me, in
> > > > > > > > > > > > > > this case the size of the long double is 128 bit
> > > > > > > > > > > > > > (copied from the host), but device reports that it
> > > > > > > > > > > > > > does not support 128 bit double. Seems to me, it is
> > > > > > > > > > > > > > a problem with the device configuration. Why does
> > > > > > > > > > > > > > the host translate long double to 128 bit fp, while
> > > > > > > > > > > > > > the device translates it to 64 bit FP?
> > > > > > > > > > > > > Sorry, I think I've misunderstood what's happening
> > > > > > > > > > > > > here, and my fix is probably wrong.
> > > > > > > > > > > > >
> > > > > > > > > > > > > For x86_64, the example from my patch summary fails
> > > > > > > > > > > > > as described there. Does that work for you?
> > > > > > > > > > > > >
> > > > > > > > > > > > > For powerpc64le, the reproducer I added to the test
> > > > > > > > > > > > > suite fails without this patch. Shouldn't it succeed?
> > > > > > > > > > > > Still, seems to me like the problem with the device
> > > > > > > > > > > > config, not the original check.
> > > > > > > > > > > > Still, seems to me like the problem with the device
> > > > > > > > > > > > config, not the original check.
> > > > > > > > > > >
> > > > > > > > > > > I'm not sure where to begin looking for that. Can you
> > > > > > > > > > > point me in the right direction? Thanks.
> > > > > > > > > > You need to understand why host and device report different
> > > > > > > > > > size of the type. Check how the device is configured in
> > > > > > > > > > lib/Basic/Targets
> > > > > > > > > Thanks for the pointer. I think I understand things a bit
> > > > > > > > > better now.
> > > > > > > > >
> > > > > > > > > Without this patch's fix, the x86_64 example from this
> > > > > > > > > patch's summary fails while this patch's new x86_64 test case
> > > > > > > > > passes. The difference is the summary's example doesn't
> > > > > > > > > specify `-unknown-linux` after `x86_64`, and that's what sets
> > > > > > > > > `hasFloat128Type()` to true.
> > > > > > > > >
> > > > > > > > > `powerpc64le-unknown-linux-gnu` does not have `__float128`,
> > > > > > > > > it seems. That's why this patch's new powerpc64le test case
> > > > > > > > > fails without this patch's fix.
> > > > > > > > >
> > > > > > > > > It seems strange to me that the code we're commenting on
> > > > > > > > > originally looks for the source type to be either
> > > > > > > > > `__float128` or 128-bit `long double`, and it then requires
> > > > > > > > > the target to support `__float128`. It doesn't accept
> > > > > > > > > 128-bit `long double` support as sufficient. My intention in
> > > > > > > > > this patch was to extend it to accept either so that all the
> > > > > > > > > examples above compile. Is that too lenient? Am I
> > > > > > > > > misinterpreting what's happening?
> > > > > > > > >
> > > > > > > > > As for your comment about 64-bit floating point in the device
> > > > > > > > > translation, I haven't seen that yet. Did I miss it?
> > > > > > > > The intention of the original patch is to make host and device
> > > > > > > > to have the same float128 and long double types. Device
> > > > > > > > inherits those types from the host to be compatible during
> > > > > > > > offloading and to correctly mangle functions.
> > > > > > > > Without this we just can't generate offloading regions
> > > > > > > > correctly. If the host has 128 bit long double, the device also
> > > > > > > > must have 128 bit long double.
> > > > > > > > If device does not support 128bit floats, in this case device
> > > > > > > > can only move the data (do load/stores ops only) and cannot do
> > > > > > > > anything else.
> > > > > > > Are you intentionally requiring support for `__float128` when the
> > > > > > > source type is 128-bit `long double`? That seems to mean
> > > > > > > powerpc64le cannot offload to itself.
> > > > > > No, if the host has 128 bit long double, the device must also have
> > > > > > 128 bit long double. It has nothing to do with the float128 type
> > > > > > itself.
> > > > > What if we change the logic to the following?
> > > > >
> > > > > ```
> > > > > (Ty->isFloat128Type() && !Context.getTargetInfo().hasFloat128Type())
> > > > > ||
> > > > > (!Ty->isFloat128Type() && Ty->isRealFloatingType() &&
> > > > > Context.getTypeSize(Ty) == 128 &&
> > > > > Context.getTargetInfo().getLongDoubleWidth() != 128)
> > > > > ```
> > > > >
> > > > > Maybe there's a more succinct way to check if `Ty` is `long
> > > > > double`....
> > > > What if `Ty` is not long double, but some other FP type?
> > > I know little about OpenMP... but does these lines take into account of
> > > 128-bit IBM extended double on powerpc{32,64}? It is the default
> > > representation of `long double`.
> > Yes, it does, it checks for any 128bit FP type.
> > What if Ty is not long double, but some other FP type?
>
> We could use something like this to be sure it's really `long double`:
>
> ```
> Ty.getUnqualifiedType() == Context.LongDoubleTy
> ```
What if we have the problem with the FP type, not the long double? Shall we
miss the check for it? I don't think so. What we need to improve, is the error
message to describe that there is a problem with 128 bit tyoe on the given
platform.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D64289/new/
https://reviews.llvm.org/D64289
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