[llvm] [AMDGPU][GlobalIsel] Add RegBankLegalize rules and lowering for G_AMDGPU_S_BUFFER_LOAD (PR #192480)

[Petar Avramovic via llvm-commits]

================
@@ -1507,14 +1679,17 @@ LLT RegBankLegalizeHelper::getBTyFromID(RegBankLLTMappingApplyID ID, LLT Ty) {
   case VgprB256:
   case UniInVgprB256:
     if (Ty == LLT::scalar(256) || Ty == LLT::fixed_vector(8, 32) ||
-        Ty == LLT::fixed_vector(4, 64) || Ty == LLT::fixed_vector(16, 16))
+        Ty == LLT::fixed_vector(4, 64) || Ty == LLT::fixed_vector(16, 16) ||
+        Ty == LLT::fixed_vector(4, LLT::pointer(1, 64)) ||
+        Ty == LLT::fixed_vector(8, LLT::pointer(3, 32)))
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petar-avramovic wrote:

this is getting too complicated, we did 
```
    if (Ty.getSizeInBits() == 160)
      return Ty;
    return LLT();
```
so just a size check should be enough

https://github.com/llvm/llvm-project/pull/192480