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

[Nikita Popov via llvm-commits]

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@@ -580,6 +582,206 @@ struct ArgumentUsesTracker : public CaptureTracker {
   const SCCNodeSet &SCCNodes;
 };
 
+// A struct of argument use: a Use and the offset it accesses. This struct
+// is to track uses inside function via GEP. If GEP has a non-constant index,
+// the Offset field is nullopt.
+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 class AccessType : uint8_t { Write, Read, Unknown };
+  AccessType ArgAccessType;
+  bool IsClobber = false;
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nikic wrote:

The "clobber" terminology here is pretty weird, because usually "clobber" means "write", while here it's more like "read".

Also, after looking at the code, I'm a bit unclear on whether we really need both AccessType::Unknown and IsClobber. Isn't one of them sufficient? 

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