[llvm] [AArch64] Add streaming-mode stack hazard optimization remarks (PR #101695)

[David Green via llvm-commits]

================
@@ -5029,3 +5050,171 @@ void AArch64FrameLowering::inlineStackProbe(MachineFunction &MF,
     MI->eraseFromParent();
   }
 }
+
+struct StackAccess {
+  enum AccessType {
+    NotAccessed = 0, // Stack object not accessed by load/store instructions.
+    GPR = 1 << 0,    // A general purpose register.
+    PPR = 1 << 1,    // A predicate register.
+    FPR = 1 << 2,    // A floating point/Neon/SVE register.
+  };
+
+  int Idx;
+  StackOffset Offset;
+  int64_t Size;
+  unsigned AccessTypes;
+
+  StackAccess() : Idx(0), Offset(), Size(0), AccessTypes(NotAccessed) {}
+
+  bool operator<(const StackAccess &Rhs) const {
+    return std::make_tuple(start(), Idx) <
+           std::make_tuple(Rhs.start(), Rhs.Idx);
+  }
+
+  bool isCPU() const {
+    // Predicate register load and store instructions execute on the CPU.
+    return AccessTypes & (AccessType::GPR | AccessType::PPR);
+  }
+  bool isSME() const { return AccessTypes & AccessType::FPR; }
+  bool isMixed() const { return ((AccessTypes & (AccessTypes - 1)) != 0); }
----------------
davemgreen wrote:

Does this handle GPR & PPR? Maybe make it simpler and just return `isCPU() && isSME()`

https://github.com/llvm/llvm-project/pull/101695