[llvm] Add FeatureFuseLiterals as SubTargetFeature for Grace and Olympus (PR #160257)

[Sushant Gokhale via llvm-commits]

sushgokh wrote:

@davemgreen I was on leave last week and couldnt work on this.

I had a look at assembly sequence again(before and after) and there are host of things going on in 'after' (not necessarily in same sequence)
1. conversion of same ldr, present in 2 immediate successors of start block, to mov+fmov
2. hoisting this sequence into the common block
3. Block merging(i.e. merge one block previously containing ldr into start block)
4. control flow optimizer pass marking one of the blocks as early exit since shrink wrapping has already happened.

I need to investigate why (2) and shrink wrapping isnt happening previously. This will take some time.

https://github.com/llvm/llvm-project/pull/160257