[llvm] [AMDGPU] Constrain use LiveMask by the operand's LaneMask for RP calculation. (PR #111452)

[Matt Arsenault via llvm-commits]

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@@ -265,14 +265,18 @@ class GCNDownwardRPTracker : public GCNRPTracker {
                const LiveRegSet *LiveRegsCopy = nullptr);
 };
 
+/// \returns the LaneMask of live lanes of \p Reg at position \p SI. Only the
+/// active lanes of \p MaxLaneMask will be set in the return value. This is
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arsenm wrote:

Seems more like a filter than MaxLaneMask? 

https://github.com/llvm/llvm-project/pull/111452