Emit a "Count" member or constant for enums

[jfroy]

We just found and fixed a major buffer overflow in a compiler caused by an out-of-date spirv op count constant. Looking at spirv.hpp, there is no machine-generate count enum member or constant for the various enums. This seems like an easy addition that would help prevent unfortunate bugs.

[johnkslang]

Do you have an example count?

Counts should have been dropped in official headers long ago, because we are now using what is effectively a sparse space, with extensions bringing in unpredictable ranges.

The model should be to switch on values you know about, but not to make arrays sized by enum values, which is the key reason the headers don't provide such a count.

[jfroy]

AMD’s compiler has arrays the size of the number of opcodes. They recently added suppprt for a bunch of spirv extensions and did not update the size of that array. They maintain a count constant because the generated headers do not.

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On Mon, Jan 21, 2019 at 15:12 John Kessenich ***@***.***> wrote: Do you have an example count? Counts should have been dropped in official headers long ago, because we are now using what is effectively a sparse space, with extensions bringing in unpredictable ranges. The model should be to switch on values you know about, but not to make arrays sized by enum values, which is the key reason they headers don't provide such a count. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#90 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AADBkqn4MEhtKrclfD-C2dnaivwwBaRCks5vFklOgaJpZM4aIuYa> .

[johnkslang]

Just opcodes? I guess you could size the array as 2^16. Any number less than that could suddenly show up as an opcode. As you note, sizing arrays this way is quite fragile, and is the reason we don't supply a count, especially since it could be immediately obsoleted by an extension, especially a non-public extension.

What about the all other enumerants?

[jfroy]

They have

• Count of BuiltIn (non-extension)
• Extension BuiltIn range (start, end)
• Op count
• ExecutionModel count
• DimCount count
• Decoration count
• StorageClass count
• Scope count
• GroupOperation count
• SourceLanguage count
• AddressingModel count
• MemoryModel count
• ExecutionMode count
• Capability count (non-extension)
• Capability extension range (start, end)
• AccessQualifier count
• MemoryAccessMask count
• MemorySemanticsMask count
• LoopControlMask count
• SelectionControlMask count
• FunctionControlMask count
• ImageFormat count (non-extension)
• ImageFormat extension count
• ImageOperandsShift count

All of these are used. In some cases, only for reflection code, but many also for codegen.