[llvm] [SPIR-V] Cache PartialOrderingVisitor in Splitter instead of rebuilding per call (PR #211198)

[Juan Manuel Martinez Caamaño via llvm-commits]

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@@ -313,12 +306,14 @@ class SPIRVStructurizerImpl {
     LoopInfo &LI;
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jmmartinez wrote:

I thought we forgot to recalculate `LoopInfo`... but it is unused.

https://github.com/llvm/llvm-project/pull/211198