[clang] [llvm] [SimplifyCFG] Not folding branch in loop header with constant iterations (PR #74268)

[via cfe-commits]

bcl5980 wrote:

> > We should add TTI check for the condition. I believe don't unroll on X86 is a correct decision. Only like AMDGPU or NVPTX these GPU backend with heavy stack cost need this.
> > And I think you need to precommit tests first.
> 
> In fact, there is no direct/strong relation with stack cost, it mostly base on unroll or not (or other loop optimizations). Maybe we should check "unroll" info (e.g #pragma unroll, any targets with this hint should try best to unroll too) before do or not do this folding. A little trouble is loop info is not well established now.

Yeah, it is a problem we unroll or not. But this case generally I believe we don't want to unroll it.

https://github.com/llvm/llvm-project/pull/74268