[llvm-dev] Proposal for string keys for address_space (original) (raw)
Leonard Chan via llvm-dev llvm-dev at lists.llvm.org
Thu Jan 10 13:53:50 PST 2019
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Hello,
We would like to propose a way for improving the diagnostics for address_space by being able to pass strings as an argument to it instead of just an integer. This was initially proposed before (http://lists.llvm.org/pipermail/cfe-dev/2018-August/058702.html) but did not focus on it at the time.
Reasoning: Clang's attribute((address_space(...))) feature uses an arbitrary integer as the discriminator of address spaces. This is effectively a global name space of integers in an API. The meaningless integers are used in diagnostics, which is not very informative. Moreover, the maintenance of the integer assignments is error-prone. It would be better if this could be a string rather than an integer. It's easy enough to pick string prefixes that distinguish the use in one part of an API from others in separately-maintained APIs, just as with symbol name prefixes in C APIs.
Goals:
- Allow for address_space to accept strings so various APIs do not need to share the same global name space of integers (address_space("API1") != address_space("API2"))
- Print the string argument instead of an integer if address_space is provided with a string for more understandable error messages.
(Possible) Implementation: Off the top of my head, it seems that a large chunk of this would be changing how address spaces are managed. Currently, it seems that all address_spaces are limited to just integers with a few spaces reserved for OpenCL and CUDA under the LangAS enum. I'm thinking that LangAS itself could be a base class with 2 different subclasses that take either integers or strings and when storing them in a qualifier, part of the address space mask could be dedicated to indicating if this LangAS is a string or integer. The only thing I can't think of is how printing the AS would work in a diagnostic since, based off the existing TypePrinter/Qualifiers::print() method, I do not think I would be able to store a reference back to some mapping of addr spaces to strings since it seems that the Qualifiers class is meant to be 32 bits long and passed by value.
I was going to come up with a proof of concept in the meantime, but wanted to ask sooner to see if anyone had ideas on this or ideas on how this could be implemented. Any feedback is welcome and I don't mind answering questions.
Thanks, Leonard
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