[PATCH] D67855: [X86] Add new calling convention that guarantees tail call optimization

[Jessica Paquette via Phabricator via llvm-commits]

paquette added inline comments.


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Comment at: llvm/docs/LangRef.rst:439-448
+"``tailcc``" - Tail callable calling convention
+    This calling convention attempts to make calls as fast as possible
+    (e.g. by passing things in registers), while also ensuring it is always
+    possible to perform tail call optimization on calls that are in tail
+    position. This calling convention allows the target to use whatever tricks
+    it wants to produce fast code for the target, without having to conform to
+    an externally specified ABI (Application Binary Interface). `Tail calls can
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dwightguth wrote:
> paquette wrote:
> > Instead of copying the documentation from `fastcc`, it might be better to say this is equivalent (other than the tail call part)
> It's not totally equivalent though... it's only equivalent to fastcc if you pass -tailcallopt. I agree with what you're proposing at a high level, but I'm not sure how to word it. Do you have a suggestion?
Maybe something like this?

"This calling convention ensures that calls in tail position will always be tail call optimized. This calling convention is equivalent to `fastcc` with an additional guarantee that tail calls will be produced whenever possible. Tail calls can only be optimized when this..."


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https://reviews.llvm.org/D67855