[llvm] [BranchFolding][RISCV] Optimize branches NE/EQ to zero or one (PR #131684)

[Craig Topper via llvm-commits]

topperc wrote:

> > Let me see if I can use optimizeCondBranch and post an update here.
> 
> There are a few problems with using `optimizeCondBranch` as is. The main issue is that the PeepholeOptimizer expects that `optimizeCondBranch` does not add an additional or remove branches. It assumes that if it optimizes the conditional branch, that it will replace it. Since `trySimplifyCondBr` often turns two branches into one, this causes the iterator in PeepholeOptimizer to break.
> 
> I suggest that we keep the two separate for now and we can address combining the two in a future patch, otherwise this patch will start touching how the PeepholeOptimizer iterates over the MBB, or will require a change to the interface of `optimizeCondBranch`.

If you just make the first branch unconditional in optimizeCondBranch will later optimizations delete dead branches after it?

https://github.com/llvm/llvm-project/pull/131684