[llvm] [GlobalISel] Add G_ADD for computeNumSignBits (PR #159202)

[Matt Arsenault via llvm-commits]

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@@ -1951,6 +1951,41 @@ unsigned GISelValueTracking::computeNumSignBits(Register R,
 
     break;
   }
+  case TargetOpcode::G_ADD: {
+    Register Src1 = MI.getOperand(1).getReg();
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arsenm wrote:

Try RHS first? 

https://github.com/llvm/llvm-project/pull/159202