[llvm] [InstCombine] Canonicalize reassoc contract fmuladd to fmul + fadd (PR #90434)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> I've added emphasis on the first condition, because we aren't currently respecting this condition in the constant folder. The constant folder will fold llvm.fmuladd as if it were a fused operation even if the target instruction set does not support FMA. 

I think we should just drop the first line in the description. The intention and implementation is to do whatever is contextually faster. A target may only choose to fuse specific callsites, and isn't required to consistently fuse every call. We can't define the IR in terms of ISA features, and just because an ISA has the features does not mean the fused operations are always faster. 




https://github.com/llvm/llvm-project/pull/90434