[llvm] [LLVM][InstCombine][AArch64] Refactor common SVE intrinsic combines. (PR #126928)

[David Sherwood via llvm-commits]

================
@@ -994,6 +994,513 @@ static std::optional<Instruction *> processPhiNode(InstCombiner &IC,
   return IC.replaceInstUsesWith(II, NPN);
 }
 
+// A collection of properties common to SVE intrinsics that allow for combines
+// to be written without needing to know the specific intrinsic.
+struct SVEIntrinsicInfo {
+  //
+  // Helper routines for common intrinsic definitions.
+  //
+
+  // e.g. llvm.aarch64.sve.add pg, op1, op2
+  //        with IID ==> llvm.aarch64.sve.add_u
+  static SVEIntrinsicInfo
+  defaultMergingOp(Intrinsic::ID IID = Intrinsic::not_intrinsic) {
+    return SVEIntrinsicInfo()
+        .setGoverningPredicateOperandIdx(0)
+        .setOperandIdxInactiveLanesTakenFrom(1)
+        .setMatchingUndefIntrinsic(IID);
+  }
+
+  // e.g. llvm.aarch64.sve.neg inactive, pg, op
+  static SVEIntrinsicInfo defaultMergingUnaryOp() {
+    return SVEIntrinsicInfo()
+        .setGoverningPredicateOperandIdx(1)
+        .setOperandIdxInactiveLanesTakenFrom(0)
+        .setOperandIdxWithNoActiveLanes(0);
+  }
+
+  // e.g. llvm.aarch64.sve.add_u pg, op1, op2
+  static SVEIntrinsicInfo defaultUndefOp() {
+    return SVEIntrinsicInfo()
+        .setGoverningPredicateOperandIdx(0)
+        .setInactiveLanesAreNotDefined();
+  }
+
+  // e.g. llvm.aarch64.sve.prf pg, ptr        (GPIndex = 0)
+  //      llvm.aarch64.sve.st1 data, pg, ptr  (GPIndex = 1)
+  static SVEIntrinsicInfo defaultVoidOp(unsigned GPIndex) {
+    return SVEIntrinsicInfo()
+        .setGoverningPredicateOperandIdx(GPIndex)
+        .setInactiveLanesAreUnused();
+  }
+
+  // e.g. llvm.aarch64.sve.cmpeq pg, op1, op2
+  //      llvm.aarch64.sve.ld1 pg, ptr
+  static SVEIntrinsicInfo defaultZeroingOp() {
+    return SVEIntrinsicInfo()
+        .setGoverningPredicateOperandIdx(0)
+        .setInactiveLanesAreUnused()
+        .setResultIsZeroInitialized();
+  }
+
+  // All properties relate to predication and thus having a general predicate
+  // is the minimum requirement to say there is intrinsic info to act on.
+  explicit operator bool() const { return hasGoverningPredicate(); }
+
+  //
+  // Properties relating to the governing predicate.
+  //
+
+  bool hasGoverningPredicate() const {
+    return GoverningPredicateIdx != std::numeric_limits<unsigned>::max();
+  }
+
+  unsigned getGoverningPredicateOperandIdx() const {
+    assert(hasGoverningPredicate() && "Propery not set!");
+    return GoverningPredicateIdx;
+  }
+
+  SVEIntrinsicInfo &setGoverningPredicateOperandIdx(unsigned Index) {
+    assert(!hasGoverningPredicate() && "Cannot set property twice!");
+    GoverningPredicateIdx = Index;
+    return *this;
+  }
+
+  //
+  // Properties relating to operations the intrinsic could be transformed into.
+  // NOTE: This does not mean such a transformation is always possible, but the
+  // knowledge makes it possible to reuse existing optimisations without needing
+  // to embed specific handling for each intrinsic. For example, instruction
+  // simplification can be used to optimise an intrinsic's active lanes.
+  //
+
+  bool hasMatchingUndefIntrinsic() const {
+    return UndefIntrinsic != Intrinsic::not_intrinsic;
+  }
+
+  Intrinsic::ID getMatchingUndefIntrinsic() const {
+    assert(hasMatchingUndefIntrinsic() && "Propery not set!");
+    return UndefIntrinsic;
+  }
+
+  SVEIntrinsicInfo &setMatchingUndefIntrinsic(Intrinsic::ID IID) {
+    assert(!hasMatchingUndefIntrinsic() && "Cannot set property twice!");
+    UndefIntrinsic = IID;
+    return *this;
+  }
+
+  //
+  // Properties relating to the result of inactive lanes.
+  //
+
+  bool inactiveLanesTakenFromOperand() const {
+    return ResultLanes == InactiveLanesTakenFromOperand;
+  }
+
+  unsigned getOperandIdxInactiveLanesTakenFrom() const {
+    assert(inactiveLanesTakenFromOperand() && "Propery not set!");
+    return OperandIdxForInactiveLanes;
+  }
+
+  SVEIntrinsicInfo &setOperandIdxInactiveLanesTakenFrom(unsigned Index) {
+    assert(ResultLanes == Uninitialized && "Cannot set property twice!");
+    ResultLanes = InactiveLanesTakenFromOperand;
+    OperandIdxForInactiveLanes = Index;
+    return *this;
+  }
+
+  bool inactiveLanesAreNotDefined() const {
+    return ResultLanes == InactiveLanesAreNotDefined;
+  }
+
+  SVEIntrinsicInfo &setInactiveLanesAreNotDefined() {
+    assert(ResultLanes == Uninitialized && "Cannot set property twice!");
+    ResultLanes = InactiveLanesAreNotDefined;
+    return *this;
+  }
+
+  bool inactiveLanesAreUnused() const {
+    return ResultLanes == InactiveLanesAreUnused;
+  }
+
+  SVEIntrinsicInfo &setInactiveLanesAreUnused() {
+    assert(ResultLanes == Uninitialized && "Cannot set property twice!");
+    ResultLanes = InactiveLanesAreUnused;
+    return *this;
+  }
+
+  // NOTE: Whilst not limited to only inactive lanes, the common use case is:
+  // inactiveLanesAreZerod =
+  //     resultIsZeroInitialized() && inactiveLanesAreUnused()
+  bool resultIsZeroInitialized() const { return ResultIsZeroInitialized; }
+
+  SVEIntrinsicInfo &setResultIsZeroInitialized() {
+    ResultIsZeroInitialized = true;
+    return *this;
+  }
+
+  //
+  // The first operand of unary merging operations is typically only used to
+  // set the result for inactive lanes. Knowing this allows us to deadcode the
+  // operand when we can prove there are no inactive lanes.
+  //
+
+  bool hasOperandWithNoActiveLanes() const {
----------------
david-arm wrote:

It's not entirely obvious to me what this name means? The way the function is used suggests this is asking if the operation has an operand used to merge values corresponding to inactive lanes into the result. How about something like `hasOperandForMergingIntoInactiveLanes`?

https://github.com/llvm/llvm-project/pull/126928