[mlir][Symbol] Change Symbol from a Trait into an OpInterface.

[rriddle]

Summary

This provides a much cleaner interface into Symbols, and allows for users to start injecting op-specific information. For example, derived op can now inject when a symbol can be discarded if use_empty. This would let us drop unused external functions, which generally have public visibility.

This revision also adds a new extraTraitClassDeclaration field to the ODS OpInterface class to allow for injecting declarations into the trait class that gets attached to the operations.

Depends On D78447

[bondhugula]

mlir/include/mlir/IR/SymbolInterfaces.td

27

Can an operation ever not have a name? Did you mean to say "A Symbol operation resides ..."?

107

"UseEmpty" seems to be an artifact of use_empty() - not perhaps a great fit here. canDiscardOnNoUses / canDiscardOnZeroUses?

124

Why is this still under a trait implementation namespace? On another note, I think verifySymbol is missing a zero region check and the code is assuming there is at least one region.

mlir/include/mlir/IR/SymbolTable.h

248–250

This information has I think gone missing from your operation interface doc comment.

mlir/lib/Transforms/SymbolDCE.cpp

81–82

Are you verifying somewhere on the op interface that a SymbolTableOp has at least one region?

[rriddle]

Resolve comments

[rriddle]

mlir/include/mlir/IR/SymbolInterfaces.td

107

This is intended to match the same verbiage as in LLVM.

124

Moved to mlir::detail. verifySymbolTable is the one that checks for regions, symbols don't need to have regions(e.g. global variables).

mlir/include/mlir/IR/SymbolTable.h

248–250

I added the link to SymbolsAndSymbolTables, which contains information on the constraints of symbols. Made an explicit mention of constraints.

mlir/lib/Transforms/SymbolDCE.cpp

81–82

Yes, this is checked as part of verifySymbolTable.

[rriddle]

Rebase

[mehdi_amini]

Can you document in the commit message the addition of extraTraitClassDeclaration? This seems like a new ODS feature independent of the symbol table change (someone using git blame in the future would end up in this commit)

[rriddle]

Rebase