[llvm] [GISel][AArch64][AMDGPU][RISCV] Canonicalize (sub X, C) -> (add X, -C) (PR #114309)

[Matt Arsenault via llvm-commits]

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@@ -2041,6 +2041,28 @@ void CombinerHelper::applyCombineMulToShl(MachineInstr &MI,
   Observer.changedInstr(MI);
 }
 
+bool CombinerHelper::matchCombineSubToAdd(MachineInstr &MI,
+                                          BuildFnTy &MatchInfo) {
+  assert(MI.getOpcode() == TargetOpcode::G_SUB && "Expected a G_SUB");
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arsenm wrote:

Yes, this should be cleaned up at some point 

https://github.com/llvm/llvm-project/pull/114309