[llvm] [DenseMap] Fix constness issues with lookup_or (PR #139247)

[Kazu Hirata via llvm-commits]

kazutakahirata wrote:

> Sorry about the thinko in the test case: should be fixed now. The included test case now fails with:
> 
> ```
> /Users/artagnon/src/llvm/llvm/include/llvm/ADT/DenseMap.h:227:12: error: cannot initialize return object of type 'unsigned int *' with an lvalue of type 'const_arg_type_t<unsigned int *>' (aka 'const unsigned int *')
>   227 |     return Default;
>       |            ^~~~~~~
> /Users/artagnon/src/llvm/llvm/unittests/ADT/DenseMapTest.cpp:677:21: note: in instantiation of member function 'llvm::DenseMapBase<llvm::DenseMap<int, unsigned int *>, int, unsigned int *, llvm::DenseMapInfo<int>, llvm::detail::DenseMapPair<int, unsigned int *>>::lookup_or' requested here
>   677 |   unsigned *Ret = M.lookup_or(0, &Default);
>       |                     ^
> ```
> 
> without the DenseMap change. The issue isn't move semantics, but rather a constness.

I've verified the same failure.

So, the issue is about unnecessarily putting `const` on the value type.  Thanks for the update and explanation!


https://github.com/llvm/llvm-project/pull/139247