[clang] [llvm] [mlir] [polly] [IR][NFC] Update IRBuilder to use InsertPosition (PR #96497)

[Nikita Popov via cfe-commits]

nikic wrote:

> > Looks like using InsertPosition in IRBuilder has some overhead:
> 
> Hm, we're adding an extra pointer chase when we give up passing a basicblock - I think then it makes sense to keep the option to pass BB+It, and do so when the caller already knows the BB (while removing the need to pass the BB around for functions that only have an instruction).

My guess here would have been that the issue is the cases where an Instruction* or BasicBlock* is passed rather than BB+Iterator, because those two cases go through an out-of-line constructor.

https://github.com/llvm/llvm-project/pull/96497