[llvm] Add the "initializes" attribute inference (PR #97373)

[Jan Voung via llvm-commits]

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@@ -580,6 +582,205 @@ struct ArgumentUsesTracker : public CaptureTracker {
   const SCCNodeSet &SCCNodes;
 };
 
+struct ArgumentUse {
+  Use *U;
+  std::optional<int64_t> Offset;
+};
+
+// A struct of argument access info. "Unknown" accesses are the cases like
+// unrecognized instructions, instructions that have more than one use of
+// the argument, or volatile memory accesses. "Unknown" implies "IsClobber"
+// and an empty access range.
+// Write or Read accesses can be clobbers as well for example, a Load with
+// scalable type.
+struct ArgumentAccessInfo {
+  enum AccessType { Write, Read, Unknown };
+  AccessType ArgAccessType;
+  ConstantRangeList AccessRanges;
+  bool IsClobber = false;
+};
+
+struct UsesPerBlockInfo {
+  DenseMap<Instruction *, ArgumentAccessInfo> Insts;
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jvoung wrote:

How large is Insts typically?

DenseMap jumps from 0 to 64: https://llvm.org/docs/ProgrammersManual.html#llvm-adt-densemap-h

SmallDenseMap<..., 8> or something might help make it more gradual 0 -> 8 -> 64

https://github.com/llvm/llvm-project/pull/97373