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Include SME attributes in the name mangling of types #290

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Include SME attributes in the name mangling of types #290

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0d1959b
Include SME attributes in the name mangling of types
kmclaughlin-arm Oct 11, 2024
44e8a55
Fix errors from check-rst-syntax
kmclaughlin-arm Oct 11, 2024
55f3e6d
- Remove suffix representing SME attributes and instead describe mang…
kmclaughlin-arm Oct 15, 2024
d71f379
- Removed separate values for preserves ZA & ZT0 as these are also ZA…
kmclaughlin-arm Oct 16, 2024
0495b41
- Corrections to example name manglings
kmclaughlin-arm Oct 17, 2024
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29 changes: 29 additions & 0 deletions aapcs64/aapcs64.rst
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Expand Up @@ -256,6 +256,7 @@ changes to the content of the document for that release.
| | September 2024 | - Add soft-float PCS variant. |
| | | - Add the __arm_get_current_vg SME support routine. |
| | | - Clarify use of `it` when preserving z and p registers. |
| | | - Update C++ mangling to include SME attributes in type names |
+------------+--------------------+------------------------------------------------------------------+

References
Expand Down Expand Up @@ -3111,6 +3112,34 @@ instead.
The SVE tuple types are mangled using their ``arm_sve.h`` names
(``svBASExN_t``).

Types which have an SME streaming or ZA interface should include an additional suffix as described in the table below:
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Adding suffixes like this would conflict with the existing mangling scheme for types. E.g. sm would normally indicate an extra short argument followed by an extra unsigned long argument (spec):

$ c++filt
_Z1fPFu10__SVInt8_tsmE
f(__SVInt8_t (*)(short, unsigned long))

I wondered whether we could use a vendor-specific qualifier (U…), but function argument types are understandably mangled without a qualifier. (For example, there is no difference between f(const int) and f(int).)

For __attribute__((arm_sve_vector_bits(N))), we used a fake template type __SVE_VLS<…, N> to attach the vector length N to the underlying standard SVE vector type. Perhaps we could do the same sort of thing here: have a fake template type that wraps the unadorned function type and adds information about the streaming mode and shared state? This would probably mean encoding that information as C++ expressions.

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Sorry, I hopelessly confused myself while writing and rewriting the comment above, so gave the wrong reason. The problem isn't that function argument types have no qualifiers, but that function types themselves have only cv-qualifiers. The spec hard-codes markup for transactional safety (Tx), but AFAIK there's no general mechanism for adding vendor extensions at the function type level.

The conclusion is the same though :-)

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We don't need to qualify functions; we don't support defining both a streaming and non-streaming function with the same signature. We only need to qualify function pointers (which, as pointers, do support qualifiers).


+-------------------------+-----------------------------+
| Type of interface | Suffix |
+=========================+=============================+
| Non-streaming (default) | None |
+-------------------------+-----------------------------+
| Streaming | sm |
+-------------------------+-----------------------------+
| Streaming-compatible | sc |
+-------------------------+-----------------------------+
| Private-ZA (default) | None |
+-------------------------+-----------------------------+
| Shared-ZA | sz |
+-------------------------+-----------------------------+

A streaming interface suffix should precede any ZA interface suffix. For example:

.. code:: c

void f(svint8_t (*fn)() __arm_inout("za") __arm_streaming) { fn(); }

is mangled as

.. code:: c

_Z1fPFu10__SVInt8_tsmszvE

.. raw:: pdf

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