Re: [PATCH] Add gnu::diagnose_as attribute

[Matthias Kretz <m.kretz@gsi.de>]

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How can we make progress here? I could try to produce some "Tony Tables" of 
diagnostic output of my modified stdx::simd. I believe it's a major 
productivity boost to see abbreviated / "obfuscated" diagnostics *out-of-the 
box* (with the possibility to opt-out). Actually, it already *is* a 
productivity boost to me. Understanding diagnostics has improved from 

"1. ooof, I'm not going to read this, let me rather guess what the issue was
2. sh** I have to read it
3. several minutes later: I finally found the five words to understand the 
problem; I could use a break"

to

"1. right, let me check that"

For reference I'll attach my stdx::simd diagnose_as patch.

We could also talk about extending the feature to provide more information 
about the diagnose_as substition. E.g. print a list of all diagnose_as 
substitutions, which were used, at the end of the output stream. Or simpler, 
print "note: some identifiers were simplified, use -fno-diagnostics-use-
aliases to see their real names".

On Tuesday, 1 June 2021 21:12:18 CEST Jason Merrill wrote:
> > Right, but then two of my design goals can't be met:
> > 
> > 1. Diagnostics have an improved signal-to-noise ratio out of the box.
> > 
> > 2. We can use replacement names that are not valid identifiers.
> 
> This is the basic disconnect: I think that these goals are
> contradictory, and that replacement names that are not valid identifiers
> will just confuse users that don't know about them.
> 
> If a user sees stdx::foo in a diagnostic and then tries to refer to
> stdx::foo and gets an error, the diagnostic is not more helpful than one
> that uses the fully qualified name.
> 
> Jonathan, David, any thoughts on this issue?

-- 
──────────────────────────────────────────────────────────────────────────
 Dr. Matthias Kretz                           https://mattkretz.github.io
 GSI Helmholtz Centre for Heavy Ion Research               https://gsi.de
 std::experimental::simd              https://github.com/VcDevel/std-simd
──────────────────────────────────────────────────────────────────────────

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diff --git a/libstdc++-v3/include/experimental/bits/simd.h b/libstdc++-v3/include/experimental/bits/simd.h
index 43331134301..8e0cceff860 100644
--- a/libstdc++-v3/include/experimental/bits/simd.h
+++ b/libstdc++-v3/include/experimental/bits/simd.h
@@ -80,13 +80,13 @@ using __m512d [[__gnu__::__vector_size__(64)]] = double;
 using __m512i [[__gnu__::__vector_size__(64)]] = long long;
 #endif
 
-namespace simd_abi {
+namespace simd_abi [[__gnu__::__diagnose_as__("simd_abi")]] {
 // simd_abi forward declarations {{{
 // implementation details:
-struct _Scalar;
+  struct [[__gnu__::__diagnose_as__("scalar")]] _Scalar;
 
 template <int _Np>
-  struct _Fixed;
+  struct [[__gnu__::__diagnose_as__("fixed_size")]] _Fixed;
 
 // There are two major ABIs that appear on different architectures.
 // Both have non-boolean values packed into an N Byte register
@@ -105,28 +105,11 @@ template <int _UsedBytes>
 template <int _UsedBytes>
   struct _VecBltnBtmsk;
 
-template <typename _Tp, int _Np>
-  using _VecN = _VecBuiltin<sizeof(_Tp) * _Np>;
-
-template <int _UsedBytes = 16>
-  using _Sse = _VecBuiltin<_UsedBytes>;
-
-template <int _UsedBytes = 32>
-  using _Avx = _VecBuiltin<_UsedBytes>;
-
-template <int _UsedBytes = 64>
-  using _Avx512 = _VecBltnBtmsk<_UsedBytes>;
-
-template <int _UsedBytes = 16>
-  using _Neon = _VecBuiltin<_UsedBytes>;
-
-// implementation-defined:
-using __sse = _Sse<>;
-using __avx = _Avx<>;
-using __avx512 = _Avx512<>;
-using __neon = _Neon<>;
-using __neon128 = _Neon<16>;
-using __neon64 = _Neon<8>;
+#if defined __i386__ || defined __x86_64__
+using __sse [[__gnu__::__diagnose_as__("[SSE]")]] = _VecBuiltin<16>;
+using __avx [[__gnu__::__diagnose_as__("[AVX]")]] = _VecBuiltin<32>;
+using __avx512 [[__gnu__::__diagnose_as__("[AVX512]")]] = _VecBltnBtmsk<64>;
+#endif
 
 // standard:
 template <typename _Tp, size_t _Np, typename...>
@@ -364,7 +347,7 @@ namespace __detail
    * users link TUs compiled with different flags. This is especially important
    * for using simd in libraries.
    */
-  using __odr_helper
+  using __odr_helper [[__gnu__::__diagnose_as__("[ODR helper]")]]
     = conditional_t<__machine_flags() == 0, _OdrEnforcer,
 		    _MachineFlagsTemplate<__machine_flags(), __floating_point_flags()>>;
 
@@ -689,7 +672,7 @@ template <typename _Abi>
   __is_avx512_abi()
   {
     constexpr auto _Bytes = __abi_bytes_v<_Abi>;
-    return _Bytes <= 64 && is_same_v<simd_abi::_Avx512<_Bytes>, _Abi>;
+    return _Bytes <= 64 && is_same_v<simd_abi::_VecBltnBtmsk<_Bytes>, _Abi>;
   }
 
 // }}}
diff --git a/libstdc++-v3/include/experimental/bits/simd_detail.h b/libstdc++-v3/include/experimental/bits/simd_detail.h
index 78ad33f74e4..1f127cd0d52 100644
--- a/libstdc++-v3/include/experimental/bits/simd_detail.h
+++ b/libstdc++-v3/include/experimental/bits/simd_detail.h
@@ -36,7 +36,7 @@
   {                                                                            \
     _GLIBCXX_BEGIN_NAMESPACE_VERSION                                           \
       namespace experimental {                                                 \
-      inline namespace parallelism_v2 {
+	inline namespace parallelism_v2 [[__gnu__::__diagnose_as__("std\u2093")]] {
 #define _GLIBCXX_SIMD_END_NAMESPACE                                            \
   }                                                                            \
   }                                                                            \