[Attributor] AAValueConstantRange: Value range analysis using constan…

…t range

Summary:
This patch introduces `AAValueConstantRange`, which answers a possible range for integer value in a specific program point.
One of the motivations is propagating existing `range` metadata. (I think we need to change the situation that `range` metadata cannot be put to Argument).

The state is a tuple of `ConstantRange` and it is initialized to (known, assumed) = ([-∞, +∞], empty).

Currently, AAValueConstantRange is created in `getAssumedConstant` method when `AAValueSimplify` returns `nullptr`(worst state).

Supported
 - BinaryOperator(add, sub, ...)
 - CmpInst(icmp eq, ...)
 - !range metadata

`AAValueConstantRange` is not intended to extend to polyhedral range value analysis.

Reviewers: jdoerfert, sstefan1

Reviewed By: jdoerfert

Subscribers: phosek, davezarzycki, baziotis, hiraditya, javed.absar, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D71620

llvm/include/llvm/Transforms/IPO/Attributor.h

@@ -105,6 +105,7 @@
 #include "llvm/Analysis/MustExecute.h"
 #include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/IR/CallSite.h"
+#include "llvm/IR/ConstantRange.h"
 #include "llvm/IR/PassManager.h"
 
 namespace llvm {
@@ -1503,6 +1504,116 @@ struct BooleanState : public IntegerStateBase<bool, 1, 0> {
   }
 };
 
+/// State for an integer range.
+struct IntegerRangeState : public AbstractState {
+
+  /// Bitwidth of the associated value.
+  uint32_t BitWidth;
+
+  /// State representing assumed range, initially set to empty.
+  ConstantRange Assumed;
+
+  /// State representing known range, initially set to [-inf, inf].
+  ConstantRange Known;
+
+  IntegerRangeState(uint32_t BitWidth)
+      : BitWidth(BitWidth), Assumed(ConstantRange::getEmpty(BitWidth)),
+        Known(ConstantRange::getFull(BitWidth)) {}
+
+  /// Return the worst possible representable state.
+  static ConstantRange getWorstState(uint32_t BitWidth) {
+    return ConstantRange::getFull(BitWidth);
+  }
+
+  /// Return the best possible representable state.
+  static ConstantRange getBestState(uint32_t BitWidth) {
+    return ConstantRange::getEmpty(BitWidth);
+  }
+
+  /// Return associated values' bit width.
+  uint32_t getBitWidth() const { return BitWidth; }
+
+  /// See AbstractState::isValidState()
+  bool isValidState() const override {
+    return BitWidth > 0 && !Assumed.isFullSet();
+  }
+
+  /// See AbstractState::isAtFixpoint()
+  bool isAtFixpoint() const override { return Assumed == Known; }
+
+  /// See AbstractState::indicateOptimisticFixpoint(...)
+  ChangeStatus indicateOptimisticFixpoint() override {
+    Known = Assumed;
+    return ChangeStatus::CHANGED;
+  }
+
+  /// See AbstractState::indicatePessimisticFixpoint(...)
+  ChangeStatus indicatePessimisticFixpoint() override {
+    Assumed = Known;
+    return ChangeStatus::CHANGED;
+  }
+
+  /// Return the known state encoding
+  ConstantRange getKnown() const { return Known; }
+
+  /// Return the assumed state encoding.
+  ConstantRange getAssumed() const { return Assumed; }
+
+  /// Unite assumed range with the passed state.
+  void unionAssumed(const ConstantRange &R) {
+    // Don't loose a known range.
+    Assumed = Assumed.unionWith(R).intersectWith(Known);
+  }
+
+  /// See IntegerRangeState::unionAssumed(..).
+  void unionAssumed(const IntegerRangeState &R) {
+    unionAssumed(R.getAssumed());
+  }
+
+  /// Unite known range with the passed state.
+  void unionKnown(const ConstantRange &R) {
+    // Don't loose a known range.
+    Known = Known.unionWith(R);
+    Assumed = Assumed.unionWith(Known);
+  }
+
+  /// See IntegerRangeState::unionKnown(..).
+  void unionKnown(const IntegerRangeState &R) { unionKnown(R.getKnown()); }
+
+  /// Intersect known range with the passed state.
+  void intersectKnown(const ConstantRange &R) {
+    Assumed = Assumed.intersectWith(R);
+    Known = Known.intersectWith(R);
+  }
+
+  /// See IntegerRangeState::intersectKnown(..).
+  void intersectKnown(const IntegerRangeState &R) {
+    intersectKnown(R.getKnown());
+  }
+
+  /// Equality for IntegerRangeState.
+  bool operator==(const IntegerRangeState &R) const {
+    return getAssumed() == R.getAssumed() && getKnown() == R.getKnown();
+  }
+
+  /// "Clamp" this state with \p R. The result is subtype dependent but it is
+  /// intended that only information assumed in both states will be assumed in
+  /// this one afterwards.
+  IntegerRangeState operator^=(const IntegerRangeState &R) {
+    // NOTE: `^=` operator seems like `intersect` but in this case, we need to
+    // take `union`.
+    unionAssumed(R);
+    return *this;
+  }
+
+  IntegerRangeState operator&=(const IntegerRangeState &R) {
+    // NOTE: `&=` operator seems like `intersect` but in this case, we need to
+    // take `union`.
+    unionKnown(R);
+    unionAssumed(R);
+    return *this;
+  }
+};
 /// Helper struct necessary as the modular build fails if the virtual method
 /// IRAttribute::manifest is defined in the Attributor.cpp.
 struct IRAttributeManifest {
@@ -1696,6 +1807,7 @@ template <typename base_ty, base_ty BestState, base_ty WorstState>
 raw_ostream &
 operator<<(raw_ostream &OS,
            const IntegerStateBase<base_ty, BestState, WorstState> &State);
+raw_ostream &operator<<(raw_ostream &OS, const IntegerRangeState &State);
 ///}
 
 struct AttributorPass : public PassInfoMixin<AttributorPass> {
@@ -2331,6 +2443,55 @@ struct AAMemoryBehavior
   static const char ID;
 };
 
+/// An abstract interface for range value analysis.
+struct AAValueConstantRange : public IntegerRangeState,
+                              public AbstractAttribute,
+                              public IRPosition {
+  AAValueConstantRange(const IRPosition &IRP)
+      : IntegerRangeState(
+            IRP.getAssociatedValue().getType()->getIntegerBitWidth()),
+        IRPosition(IRP) {}
+
+  /// Return an IR position, see struct IRPosition.
+  const IRPosition &getIRPosition() const override { return *this; }
+
+  /// See AbstractAttribute::getState(...).
+  IntegerRangeState &getState() override { return *this; }
+  const AbstractState &getState() const override { return *this; }
+
+  /// Create an abstract attribute view for the position \p IRP.
+  static AAValueConstantRange &createForPosition(const IRPosition &IRP,
+                                                 Attributor &A);
+
+  /// Return an assumed range for the assocaited value a program point \p CtxI.
+  /// If \p I is nullptr, simply return an assumed range.
+  virtual ConstantRange
+  getAssumedConstantRange(Attributor &A,
+                          const Instruction *CtxI = nullptr) const = 0;
+
+  /// Return a known range for the assocaited value at a program point \p CtxI.
+  /// If \p I is nullptr, simply return a known range.
+  virtual ConstantRange
+  getKnownConstantRange(Attributor &A,
+                        const Instruction *CtxI = nullptr) const = 0;
+
+  /// Return an assumed constant for the assocaited value a program point \p
+  /// CtxI.
+  Optional<ConstantInt *>
+  getAssumedConstantInt(Attributor &A, const Instruction *CtxI = nullptr) const {
+    ConstantRange RangeV = getAssumedConstantRange(A, CtxI);
+    if (auto *C = RangeV.getSingleElement())
+      return cast<ConstantInt>(
+          ConstantInt::get(getAssociatedValue().getType(), *C));
+    if (RangeV.isEmptySet())
+      return llvm::None;
+    return nullptr;
+  }
+
+  /// Unique ID (due to the unique address)
+  static const char ID;
+};
+
 } // end namespace llvm
 
 #endif // LLVM_TRANSFORMS_IPO_FUNCTIONATTRS_H