[llvm] [GlobalISel] Correct comment about type vs register class (PR #116083)

[Matt Arsenault via llvm-commits]

================
@@ -147,6 +147,16 @@ void GISelKnownBits::computeKnownBitsImpl(Register R, KnownBits &Known,
   unsigned Opcode = MI.getOpcode();
   LLT DstTy = MRI.getType(R);
 
+  // Handle the case where this is called on a register that does not have a
+  // type constraint (i.e. it's a target instruction with a register class
+  // constraint instead). This is unlikely to occur except by looking through
----------------
arsenm wrote:

Even if you're introducing concrete register classes earlier than selection, it shouldn't hurt to add an LLT there 

https://github.com/llvm/llvm-project/pull/116083