[llvm] [AMDGPU][GlobalISel] Add RegBankLegalize support for G_MUL (PR #177314)

[Matt Arsenault via llvm-commits]

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@@ -681,6 +681,27 @@ bool RegBankLegalizeHelper::lowerSplitTo32(MachineInstr &MI) {
   return true;
 }
 
+bool RegBankLegalizeHelper::lowerSplitTo32Mul(MachineInstr &MI) {
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arsenm wrote:

It's unfortunate this isnt' shared with LegalizerHelper 

https://github.com/llvm/llvm-project/pull/177314