[llvm] [ADT] Extract DenseMapStorage from DenseMap (NFC) (PR #226664)

[Fangrui Song via llvm-commits]

MaskRay wrote:

Thanks for the numbers. After the rebase I measure +0.71% / +0.84% / +0.56% instructions:u on Metadata/NewGVN/ScalarEvolution, which matches your +0.65%, so I'm fine with this as an intermediate step if the CRTP removal follows. Could you push that branch somewhere so I can reproduce the −0.3% and −67 lines?

One thing to fix: the gdb/lldb/natvis formatters (llvm/utils/gdb-scripts/prettyprinters.py, llvm/utils/lldbDataFormatters.py, llvm/utils/LLVMVisualizers/llvm.natvis) read Buckets/Used/NumEntries/NumBuckets directly on DenseMap. They now need to go through Storage.

https://github.com/llvm/llvm-project/pull/226664