[PATCH] D51463: Fix a couple of mangling canonicalizer corner case bugs.

[Richard Smith - zygoloid via Phabricator via llvm-commits]

rsmith added a comment.

In https://reviews.llvm.org/D51463#1223631, @erik.pilkington wrote:

> I think there may be some more (many?) similar bugs to this. Possible testcase: `_Z1fI1SEiS0_T_` and `_Z1fI1SEiS0_S0_`. I think these will be considered equivalent to the canonicalizer because their representation is structurally equivalent, but they are in fact distinct.


Yes, you're right; I think we should be preserving the fact that the type was named via a reference to a specific template parameter in the AST, since that's part of the semantics of the mangled name, and clients that aren't demanglers will sometimes care about the difference. (Also, I would like the demangler to have a mode where it /doesn't/ substitute template parameters for their values, as that's basically never what I personally want when demangling a name.)

Doing that has some complications: if we say that `1XIiE` and `1YIiE` are the same, does that mean that `1YIT_E` is in the same equivalence class too, in the case where `T_` is `i`? (I think the answer should be "no", but this does not seem obvious.)

The good news is that this patch is sufficient to ensure that all interesting function and variable manglings in at least clang and llvm demangle to non-equivalent trees. (We still have duplicate ASTs for virtual function thunks, but I'm certainly happy to defer addressing that until we have a need.)


Repository:
  rL LLVM

https://reviews.llvm.org/D51463