[llvm] promote Pseduo Opcode from 32bit to 64bits after eliminating the `extsw` instruction in PPCMIPeepholes optimization (PR #85451)

[Kamau Bridgeman via llvm-commits]

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@@ -5234,6 +5234,244 @@ bool PPCInstrInfo::isTOCSaveMI(const MachineInstr &MI) const {
 // We limit the max depth to track incoming values of PHIs or binary ops
 // (e.g. AND) to avoid excessive cost.
 const unsigned MAX_BINOP_DEPTH = 1;
+
+// The `PromoteInstr32To64ForEmliEXTSW` function is recursive. The parameter
+// BinOpDepth  does not count all of the recursions. The parameter BinOpDepth is
+// incremented  only when `PromoteInstr32To64ForEmliEXTSW` calls itself more
+// than once. This is done to prevent exponential recursion. The function will
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kamaub wrote:

We should probably only mention the recursion after explaining how we follow the register uses below.

https://github.com/llvm/llvm-project/pull/85451