[PATCH] D102369: [ASTMatchers][NFC] Remove runtime checks where compile time is sufficient

[Nathan James via Phabricator via cfe-commits]

njames93 added a comment.

In D102369#2756493 <https://reviews.llvm.org/D102369#2756493>, @aaron.ballman wrote:

> I'm not opposed, but I don't know that this is really an improvement. We've gone from a pretty simple code pattern to needing to spell out the type twice with a type_trait, and all that we save is a call to `isa<>` within the casting operation. While I agree this is strictly executing less code, it's morally the same as the usual antipattern of "isa followed by cast should be a dyn_cast". Is there evidence that this is a big performance win?



In D102369#2756493 <https://reviews.llvm.org/D102369#2756493>, @aaron.ballman wrote:

> I'm not opposed, but I don't know that this is really an improvement. We've gone from a pretty simple code pattern to needing to spell out the type twice with a type_trait, and all that we save is a call to `isa<>` within the casting operation. While I agree this is strictly executing less code, it's morally the same as the usual antipattern of "isa followed by cast should be a dyn_cast". Is there evidence that this is a big performance win?

To be honest, it would be much nicer if we could specialise `isa` to return false if there is From type is not a base class of the To type. However I'm not sure if that would break anything else.
It's all part of the "Don't do at runtime whats known at compile time


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https://reviews.llvm.org/D102369