[llvm] [GlobalISel] Add iterative known-bits evaluation to GISelValueTracking (PR #221755)

[Matt Arsenault via llvm-commits]

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@@ -38,6 +38,13 @@ class LLVM_ABI GISelValueTracking : public GISelChangeObserver {
   const DataLayout &DL;
   unsigned MaxDepth;
 
+  // The triple (Register, DemandedElts, Depth) used as worklist and cache key.
+  using WorkItem = std::tuple<Register, APInt, unsigned>;
+  // Items pending evaluation during the active top-level query.
+  SmallVector<WorkItem> Stack;
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arsenm wrote:

make the size the max stack depth 

https://github.com/llvm/llvm-project/pull/221755