[llvm] [DAGCombiner] Allow freeze(fmul) + fadd/fsub → FMA when using contract (PR #142250)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

DAGCombiner::visitFREEZE has a list of "AllowMultipleMaybePoisonOperands" opcodes where it will try to force the freeze through the op and onto all its operandss - I've never been sure of the requirements for this list (or why we don't perform it for all non-poison-generating ops) - but if its permissible to add FMUL to it then that might be a much simpler solution. 

https://github.com/llvm/llvm-project/pull/142250