aaron.ballman added inline comments.
================
Comment at: include/clang/Basic/Attr.td:894
@@ -893,1 +893,3 @@
+def DisableTailCalls : InheritableAttr {
+ let Spellings = [GNU<"disable_tail_calls">,
----------------
Pardon me if this is obvious, but -- are there times when you would want to
disable tail calls but leave other optimizations in place? I'm trying to
understand why these attributes are orthogonal.
================
Comment at: include/clang/Basic/Attr.td:896
@@ +895,3 @@
+ let Spellings = [GNU<"disable_tail_calls">,
+ CXX11<"clang", "disable_tail_calls">];
+ let Subjects = SubjectList<[Function, ObjCMethod]>;
----------------
Should this attribute be plural? Are there multiple tail calls within a single
method that can be optimized away?
================
Comment at: include/clang/Basic/AttrDocs.td:1619
@@ +1618,3 @@
+ let Content = [{
+Use ``__attribute__((disable_tail_calls)))`` to instruct the backend not to do
tail call optimization.
+ }];
----------------
I would avoid using the exact syntax here because this is a GNU and C++
attribute. Could just say:
The ``disable_tail_calls`` attribute instructs the backend to not perform tail
call optimization.
================
Comment at: lib/Sema/SemaDeclAttr.cpp:4882
@@ +4881,3 @@
+ case AttributeList::AT_DisableTailCalls:
+ handleSimpleAttribute<DisableTailCallsAttr>(S, D, Attr);
+ break;
----------------
Okay, that makes sense. I can contrive examples of noreturn where TCO could
happen, it just took me a while to think of them. ;-)
What about other semantic checks, like warning the user about disabling TCO
when TCO could never be enabled in the first place? Can you disable TCO for
functions that are marked __attribute__((naked))? What about returns_twice?
Unfortunately, we have a lot of attributes for which we've yet to write
documentation, so you may need to look through Attr.td.
http://reviews.llvm.org/D12547
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