ychen added inline comments.
================
Comment at: clang/lib/Sema/SemaTemplateDeduction.cpp:5511-5539
+ template <typename T1, typename T2,
+ std::enable_if_t<std::is_same<T1, T2>::value, bool> = true>
+ bool operator()(T1 *PS1, T2 *PS2) {
+ return hasEqualTemplateArgumentList(
+ PS1->getTemplateArgsAsWritten()->arguments(),
+ PS2->getTemplateArgsAsWritten()->arguments());
+ }
----------------
mizvekov wrote:
> I think you are not supposed to use the `TemplateArgsAsWritten` here.
>
> The injected arguments are 'Converted' arguments, and the transformation
> above, by unpacking the arguments, is reversing just a tiny part of the
> conversion process.
>
> It's not very meaningful to canonicalize the arguments as written to perform
> a semantic comparison, as that works well just for some kinds of template
> arguments, like types and templates, but not for other kinds in which the
> conversion process is not trivial.
>
> For example, I think this may fail to compare the same integers written in
> different ways, like `2` vs `1 + 1`.
Indeed. It can happen only when comparing one partial specialization with
another. I think the standard does not require an implementation to deal with
this but we could use the best effort without much overhead. For `2` vs `1+1`
or similar template arguments that are not dependent, we could assume the
equivalence because they wouldn't be in the partial ordering stage if they're
not equivalent. For more complicated cases like `J+2` vs `J+1+1` where J is
NTTP, let's stop trying (match GCC) because the overhead is a little bit high.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D128750/new/
https://reviews.llvm.org/D128750
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