[PATCH] D145088: [RISCV] Add attribute(riscv_rvv_vector_bits(N)) based on AArch64 arm_sve_vector_bits.

[Erich Keane via Phabricator via cfe-commits]

erichkeane added inline comments.


================
Comment at: clang/test/SemaCXX/attr-riscv-rvv-vector-bits.cpp:12
+
+template<typename T> struct S { T var; };
+
----------------
craig.topper wrote:
> erichkeane wrote:
> > craig.topper wrote:
> > > @erichkeane does this cover the dependent case or were you looking for something else?
> > > 
> > > Here are on the only mentions of template I see in SVE tests that use this attribute.
> > > 
> > > ```
> > > clang/test$ ack template `ack arm_sve_vector -l`
> > > CodeGenCXX/aarch64-mangle-sve-fixed-vectors.cpp
> > > 37:template <typename T> struct S {};
> > > 
> > > SemaCXX/attr-arm-sve-vector-bits.cpp
> > > 16:template<typename T> struct S { T var; };
> > > ```
> > > 
> > > Here is the result for this patch
> > > 
> > > ```
> > > clang/test$ ack template `ack riscv_rvv_vector -l`
> > > CodeGenCXX/riscv-mangle-rvv-fixed-vectors.cpp
> > > 48:template <typename T> struct S {};
> > > 
> > > SemaCXX/attr-riscv-rvv-vector-bits.cpp
> > > 12:template<typename T> struct S { T var; };
> > > ```
> > Thats unfortunate, and I wish I'd thought of it at the time/been more active reviewing the SVE stuff then.  Really what I'm looking for is:
> > 
> > ```
> > template<int N> 
> > struct Whatever {
> >   using Something = char __attribute((riscv_rvv_vector_bits(N)));
> > };
> > 
> > void Func(Whatever<5>::Something MyVar){}
> > 
> > ```
> That does not appear to work.
> 
> ```
> $ ./bin/clang test.cpp --target=riscv64 -march=rv64gcv -mrvv-vector-bits=zvl
> test.cpp:3:41: error: 'riscv_rvv_vector_bits' attribute requires an integer constant
>     using Something = char __attribute((riscv_rvv_vector_bits(N)));
> ```
> 
> It's not very useful as a template parameter. There's only one value that works and that's whatever __RISCV_RVV_VLEN_BITS is set to.
Thats really unfortunate, but it makes me wonder what `DependentVectorType ` is for in this case, or the handling of said things.  Because I would expect:

```
template<typename T, int Size>
using RiscvVector = T __attribute__((risv_rvv_vector_bits(Size)));

RiscvVector<char, <TheRightAnswer>> Foo;
```
to be useful.  Even if not, I'd expect:
```
template<typename T>
using RiscvVector = T __attribute__((risv_rvv_vector_bits(TheRightAnswer)));
RiscvVector<char> Foo;
```
to both work.

>>It's not very useful as a template parameter. There's only one value that works and that's whatever __RISCV_RVV_VLEN_BITS is set to.
This makes me wonder why this attribute takes an integer constant anyway, if it is just a 'guess what the right answer is!' sorta thing.  Seems to me this never should have taken a parameter.


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  https://reviews.llvm.org/D145088/new/

https://reviews.llvm.org/D145088