sdesmalen marked an inline comment as done.
sdesmalen added inline comments.


================
Comment at: clang/test/CodeGen/aarch64-sve-intrinsics/negative/acle_sve_ext.c:1
+// RUN: %clang_cc1 -triple aarch64-none-linux-gnu -target-feature +sve 
-fallow-half-arguments-and-returns -fsyntax-only -verify -D__ARM_FEATURE_SVE %s
+
----------------
SjoerdMeijer wrote:
> sdesmalen wrote:
> > SjoerdMeijer wrote:
> > > sdesmalen wrote:
> > > > SjoerdMeijer wrote:
> > > > > Just curious about the `-fallow-half-arguments-and-returns`, do you 
> > > > > need that here?
> > > > > 
> > > > > And if not here, why do you need it elsewhere (looks enabled on all 
> > > > > tests)?
> > > > It's not needed for this test, but we've generated most of our tests 
> > > > from the ACLE spec and the tests that use a scalar float16_t (== 
> > > > __fp16) will need this, such as the ACLE intrinsic:
> > > > 
> > > >   svfloat16_t svadd_m(svbool_t, svfloat16_t, float16_t);
> > > > 
> > > > If you feel strongly about it, I could remove it from the other RUN 
> > > > lines.
> > > Well, I think this is my surprise then. Thinking out loud: we're talking 
> > > SVE here, which always implies FP16. That's why I am surprised that we 
> > > bother with a storage-type only type. Looking at the SVE ACLE I indeed 
> > > see:
> > > 
> > >   float16_t equivalent to __fp16
> > > 
> > > where I was probably expecting:
> > > 
> > >   float16_t equivalent to _Float16
> > > 
> > > and with that everything would be sorted I guess, then we also don't need 
> > > the hack^W workaround that is `-fallow-half-arguments-and-returns`. But 
> > > maybe there is a good reason to use/choose `__fp16` that I don't see 
> > > here. Probably worth a quick question for the ARM SVE ACLE, would you 
> > > mind quickly checking?
> > > 
> > > 
> > As just checked with @rsandifo-arm, the reason is that the definition of 
> > `float16_t` has to be compatible with `arm_neon.h`, which uses `__fp16` for 
> > both Clang and GCC.
> I was suspecting it was compatability reasons, but perhaps not with 
> `arm_neon.h`. So what exactly does it mean to be compatible with arm_neon.h? 
> I mean, put simply and naively, if you target SVE, you include arm_sve.h, and 
> go from there. How does that interact with arm_neon.h and why can float16_t 
> not be a proper half type? 
If you target SVE, you can still use Neon instructions, so it's still possible 
to include arm_neon.h as well. If those have differing definitions of 
float16_t, that may give trouble when using builtins from both the Neon and SVE 
header files.


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  https://reviews.llvm.org/D76679/new/

https://reviews.llvm.org/D76679



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