[llvm] [AMDGPU][DAGCombiner][GlobalISel] Prevent FMA contraction when multiply cannot be eliminated (PR #169735)

[Matt Arsenault via llvm-commits]

================
@@ -6208,6 +6208,102 @@ static bool hasMoreUses(const MachineInstr &MI0, const MachineInstr &MI1,
                        MRI.use_instr_nodbg_end());
 }
 
+/// Check if all uses of a multiply instruction can be contracted into FMAs.
+/// This prevents creating FMAs when the multiply has other uses that can't
+/// be contracted, which would duplicate the multiply computation.
+static bool allMulUsesCanBeContracted(const MachineInstr &MulMI,
----------------
arsenm wrote:

I doubt any of the globalisel path is covered in existing tests 

https://github.com/llvm/llvm-project/pull/169735