FAQ entry about value names #180
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| @@ -179,3 +179,7 @@ use in `test.op`), whereas iterating on the "users" of `%0` would yield directly | |||
| twice a user of `%0`, it's up to the call site to use a set to unique these if needed. | |||
| [The tutorial on use-def chains](https://mlir.llvm.org/docs/Tutorials/UnderstandingTheIRStructure/#traversing-the-def-use-chains) may help understand the details as well. | |||
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| ## How to programmatically obtain the "name" of the SSA value (`%foo`)? | |||
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| It is impossible in general. The values names are _not part of the IR_ and are only there to make textual representation of the IR easier for humans to read. They are generated by the IR printer on-the-fly and may differ depending on the printer configuration. It is, however, possible to ask the printer to generate specific names by having the operation that defines the value implement [`OpAsmOpInterface`](https://github.com/llvm/llvm-project/blob/main/mlir/include/mlir/IR/OpAsmInterface.td). | |||
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But even if you specify a name, when there is a clash, the printer will insert a counter to the end (ex. %foo1) to avoid clashes. So even in that case, it is not possible to always get the name.
Perhaps just allude to the fact that those are not names, but counters, would make it easier to understand.
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I would use "identifier" instead of "counters" I think (the latter makes me think it’s numerical)
(but maybe "identifier" does not help to express clearly what you're looking for by going away from "name")
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Identifier implies identity... Rephrased to mention specifically that one can control the prefix.
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"identity" seems right though: in the textual format it is supposed to be exactly this isn't it?
| @@ -179,3 +179,7 @@ use in `test.op`), whereas iterating on the "users" of `%0` would yield directly | |||
| twice a user of `%0`, it's up to the call site to use a set to unique these if needed. | |||
| [The tutorial on use-def chains](https://mlir.llvm.org/docs/Tutorials/UnderstandingTheIRStructure/#traversing-the-def-use-chains) may help understand the details as well. | |||
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| ## How to programmatically obtain the "name" of the SSA value (`%foo`)? | |||
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| It is impossible in general. The values names are _not part of the IR_ and are only there to make textual representation of the IR easier for humans to read. They are generated by the IR printer on-the-fly and may differ depending on the printer configuration. It is, however, possible to ask the printer to generate specific names by having the operation that defines the value implement [`OpAsmOpInterface`](https://github.com/llvm/llvm-project/blob/main/mlir/include/mlir/IR/OpAsmInterface.td). | |||
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I'd not say its impossible (you can create the AsmState, print, retrieve, create map and well, technically, reuse the AsmState to ensure it is kept, but given the naming is deterministic, if you are doing a non-local variant it should remain the same). That's not the problem, the problem is folks having an expectation that it is consistent across mutations etc. The expectation of these being "attached" names that are somehow fixed is more problematic.
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Can you mdformat? |
This question gets asked a lot so clarify that names are not part of the IR.
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Github doesn't seem to pick up the changes, here's the branch: main...ftynse-patch-1 |
This question gets asked a lot so clarify that names are not part of the IR.