[llvm] [RISCV][VLOPT] Enable the RISCVVLOptimizer by default (PR #119461)

[Craig Topper via llvm-commits]

topperc wrote:

> > > Should we just remove this code for now
> > 
> > 
> > This would be fine by me. Incrementalism is good. :)
> 
> I've removed it in #120291.
> 
> FWIW, I don't think what you're concerned about can happen with or without #120291 merged since all the instructions that isVectorOpUsedAsScalarOp deal with return `OperandInfo(Unknown)` and won't lead to any (incorrect) optimization.

The code that was there said that we could ignore the reduction and not call getOperandInfo on it. It effectively said that a scalar operand doesn't depend on any elements from the producer. This is incorrect, it demands exactly 1 element. With that code in place only the VL of the other consumers was used. If they used less than 1 element then the 1 element that scalar op needs wouldn't be valid.

https://github.com/llvm/llvm-project/pull/119461