[llvm] [AMDGPU] Add regbankselect rules for G_ADD/SUB and variants (PR #159860)

[Petar Avramovic via llvm-commits]

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@@ -77,10 +77,14 @@ body: |
     ; CHECK-NEXT: [[C2:%[0-9]+]]:sgpr(s32) = G_CONSTANT i32 0
     ; CHECK-NEXT: [[SELECT:%[0-9]+]]:sgpr(s32) = G_SELECT [[AND]](s32), [[C1]], [[C2]]
     ; CHECK-NEXT: [[TRUNC:%[0-9]+]]:sgpr(s16) = G_TRUNC [[SELECT]](s32)
+    ; CHECK-NEXT: [[C3:%[0-9]+]]:sgpr(s16) = G_CONSTANT i16 255
+    ; CHECK-NEXT: [[AND1:%[0-9]+]]:sgpr(s16) = G_AND [[TRUNC]], [[C3]]
     %0:_(s32) = COPY $sgpr0
     %1:_(s32) = COPY $sgpr1
     %2:_(s1) = G_ICMP intpred(eq), %0, %1
     %3:_(s16) = G_SEXT %2
+    %4:_(s16) = G_CONSTANT i16 255
+    %5:_(s16) = G_AND %3, %4
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petar-avramovic wrote:

last nit from me, applies to most of the mir tests can make it a bit shorter
```suggestion
    %4:_(s16) = G_AND %3, %3
```

https://github.com/llvm/llvm-project/pull/159860