[llvm] [WIP][AMDGPU][Attributor] Infer `inreg` attribute in `AMDGPUAttributor` (PR #101609)

[Shilei Tian via llvm-commits]

================
@@ -1009,6 +1009,82 @@ struct AAAMDGPUNoAGPR
 
 const char AAAMDGPUNoAGPR::ID = 0;
 
+struct AAAMDGPUInreg
+    : public IRAttribute<Attribute::InReg,
+                         StateWrapper<BooleanState, AbstractAttribute>,
+                         AAAMDGPUInreg> {
+  AAAMDGPUInreg(const IRPosition &IRP, Attributor &A) : IRAttribute(IRP) {}
+
+  /// Create an abstract attribute view for the position \p IRP.
+  static AAAMDGPUInreg &createForPosition(const IRPosition &IRP, Attributor &A);
+
+  /// See AbstractAttribute::getName()
+  const std::string getName() const override { return "AAAMDGPUInreg"; }
+
+  const std::string getAsStr(Attributor *A) const override {
+    return getAssumed() ? "inreg" : "non-inreg";
+  }
+
+  void trackStatistics() const override {}
+
+  /// See AbstractAttribute::getIdAddr()
+  const char *getIdAddr() const override { return &ID; }
+
+  /// This function should return true if the type of the \p AA is AAAMDGPUInreg
+  static bool classof(const AbstractAttribute *AA) {
+    return (AA->getIdAddr() == &ID);
+  }
+
+  /// Unique ID (due to the unique address)
+  static const char ID;
+};
+
+const char AAAMDGPUInreg::ID = 0;
+
+namespace {
+
+struct AAAMDGPUInregArgument : public AAAMDGPUInreg {
+  AAAMDGPUInregArgument(const IRPosition &IRP, Attributor &A)
+      : AAAMDGPUInreg(IRP, A) {}
+
+  void initialize(Attributor &A) override {
+    if (getAssociatedArgument()->hasAttribute(Attribute::InReg))
+      indicateOptimisticFixpoint();
+  }
+
+  ChangeStatus updateImpl(Attributor &A) override {
+    const auto &InfoCache =
+        static_cast<AMDGPUInformationCache &>(A.getInfoCache());
+    unsigned ArgNo = getAssociatedArgument()->getArgNo();
+
+    auto Pred = [&](AbstractCallSite ACS) -> bool {
+      CallBase *CB = ACS.getInstruction();
+      auto TTI = InfoCache.TM.getTargetTransformInfo(*CB->getFunction());
+      Value *V = CB->getArgOperandUse(ArgNo);
+      return TTI.isAlwaysUniform(V);
----------------
shiltian wrote:

Need to get the potential value and then check the uniformity.

https://github.com/llvm/llvm-project/pull/101609