[PATCH] D105807: [X86] pr51000 struct return tailcalling

[Nathan Sidwell via Phabricator via llvm-commits]

urnathan added a comment.



> Do we need a way to query the backend? eg. expose `IsEligibleForTailCallOptimization()` or similar to front-ends like Clang?

In general that's not possible until we've done code generation.  (a) the middle end is responsible for determing a bunch of 'can tail-call' pieces (like local variable liveness at the point of the call).  The backend is responsible for determining other items (like 'this is a cross-SO call'.  Heck, code generation might not be being done in the same process as the compiler invocation -- LTO is a thing :).

I think there are two types of tail-call failure.
a) middle-end says no -- eg, a local stack-resident variable is live across the call.
b) the back-end says no -- eg, we have a cross-SO call here (and the got-pointer is callee-save).


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https://reviews.llvm.org/D105807