[clang] [llvm] [LICM] Sink unused l-invariant loads in preheader. (PR #157559)

[Sirish Pande via llvm-commits]

srpande wrote:

> > > Unused loop invariant loads were not sunk from preheader to exit block, increasing live range.
> > 
> > 
> > What live range? If the result is unused, how can it contribute to register pressure in the loop body?
> 
> I believe "unused" here refers to "unused inside the loop, but used after the loop".

That is true. With the large loop body (possibly unrolled), "live range" got extended instruction from preheader got moved passed the body of the loop after this sunk subpass.

https://github.com/llvm/llvm-project/pull/157559