[llvm] AMDGPU/GlobalISel: Add skeletons for new register bank select passes (PR #112862)

[Petar Avramovic via llvm-commits]

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@@ -1371,7 +1378,12 @@ void GCNPassConfig::addPreRegBankSelect() {
 }
 
 bool GCNPassConfig::addRegBankSelect() {
-  addPass(new AMDGPURegBankSelect());
+  if (NewRegBankSelect) {
+    addPass(createAMDGPURBSelectPass());
+    addPass(createAMDGPURBLegalizePass());
+  } else {
+    addPass(new AMDGPURegBankSelect());
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petar-avramovic wrote:

Older versions were doing that. New passes are much simpler and don't use anything from generic reg-bank-select(except register banks that come from td file via RegisterBankInfo).
To simplify review process and transition period I would prefer two passes separate from AMDGPURegBankSelect, rb-legalize will also be split across few files.
Old behavior is there to keep upcoming patches small by gradually switching to -new-reg-bank-select. 

https://github.com/llvm/llvm-project/pull/112862