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

[Matt Arsenault via llvm-commits]

arsenm wrote:

> Here's something that looks like a clear bug in the front end -- the front end will generate the llvm.fmuladd() intrinsic even if I've explicitly disabled FMA with the -mno-fma option!

I say this is not a bug. The -m flags change the behavior of the machine/codegen, and in this case no FMA instruction was emitted as requested. It was a mechanical request to not emit the FMA instruction. It was not a semantic request to not fuse operations (i.e. not a -f flag)

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