[clang] [Clang] Track alloca element types to avoid getAllocatedType() calls (PR #181740)

[Jameson Nash via cfe-commits]

vtjnash wrote:

@ojhunt I'm assuming I can bypass your requested changes based on your comment, but if you get a chance to clear that flag yourself, that would be appreciated

https://github.com/llvm/llvm-project/pull/181740