[mlir][IntRange] Poison support in int-range analysis

mlir/include/mlir/Dialect/Arith/Transforms/Passes.td

@@ -49,7 +49,8 @@ def ArithIntRangeOpts : Pass<"int-range-optimizations"> {
   // Explicitly depend on "arith" because this pass could create operations in
   // `arith` out of thin air in some cases.
   let dependentDialects = [
-    "::mlir::arith::ArithDialect"
+    "::mlir::arith::ArithDialect",
+    "::mlir::ub::UBDialect"
   ];
 }
 

mlir/include/mlir/Dialect/UB/IR/UBOps.h

@@ -12,6 +12,7 @@
 #include "mlir/Bytecode/BytecodeOpInterface.h"
 #include "mlir/IR/Dialect.h"
 #include "mlir/IR/OpImplementation.h"
+#include "mlir/Interfaces/InferIntRangeInterface.h"
 #include "mlir/Interfaces/SideEffectInterfaces.h"
 
 #include "mlir/Dialect/UB/IR/UBOpsInterfaces.h.inc"

mlir/include/mlir/Dialect/UB/IR/UBOps.td

@@ -9,8 +9,9 @@
 #ifndef MLIR_DIALECT_UB_IR_UBOPS_TD
 #define MLIR_DIALECT_UB_IR_UBOPS_TD
 
-include "mlir/Interfaces/SideEffectInterfaces.td"
 include "mlir/IR/AttrTypeBase.td"
+include "mlir/Interfaces/InferIntRangeInterface.td"
+include "mlir/Interfaces/SideEffectInterfaces.td"
 
 include "mlir/Dialect/UB/IR/UBOpsInterfaces.td"
 
@@ -39,7 +40,8 @@ def PoisonAttr : UB_Attr<"Poison", "poison", [PoisonAttrInterface]> {
 // PoisonOp
 //===----------------------------------------------------------------------===//
 
-def PoisonOp : UB_Op<"poison", [ConstantLike, Pure]> {
+def PoisonOp : UB_Op<"poison", [ConstantLike, Pure,
+  DeclareOpInterfaceMethods<InferIntRangeInterface, ["inferResultRanges"]>]> {
   let summary = "Poisoned constant operation.";
   let description = [{
     The `poison` operation materializes a compile-time poisoned constant value

mlir/include/mlir/Dialect/Vector/IR/VectorOps.td

@@ -843,7 +843,7 @@ def Vector_FromElementsOp : Vector_Op<"from_elements", [
 
 def Vector_InsertOp :
   Vector_Op<"insert", [Pure,
-     DeclareOpInterfaceMethods<InferIntRangeInterface, ["inferResultRanges"]>,
+     DeclareOpInterfaceMethods<InferIntRangeInterface, ["inferResultRangesFromOptional"]>,
      PredOpTrait<"source operand and result have same element type",
                  TCresVTEtIsSameAsOpBase<0, 0>>,
      AllTypesMatch<["dest", "result"]>]> {

mlir/include/mlir/Interfaces/InferIntRangeInterface.h

@@ -51,6 +51,9 @@ class ConstantIntRanges {
   /// The maximum value of an integer when it is interpreted as signed.
   const APInt &smax() const;
 
+  /// Get the bitwidth of the ranges.
+  unsigned getBitWidth() const;
+
   /// Return the bitwidth that should be used for integer ranges describing
   /// `type`. For concrete integer types, this is their bitwidth, for `index`,
   /// this is the internal storage bitwidth of `index` attributes, and for
@@ -62,6 +65,10 @@ class ConstantIntRanges {
   /// sint_max(width)].
   static ConstantIntRanges maxRange(unsigned bitwidth);
 
+  /// Create a poisoned range, poisoned ranges are propagated through the DAG
+  /// and will cause the immediate UB if reached the side-effecting operation.
+  static ConstantIntRanges poison(unsigned bitwidth);
+
   /// Create a `ConstantIntRanges` with a constant value - that is, with the
   /// bounds [value, value] for both its signed interpretations.
   static ConstantIntRanges constant(const APInt &value);
@@ -96,6 +103,16 @@ class ConstantIntRanges {
   /// value.
   std::optional<APInt> getConstantValue() const;
 
+  /// Returns true if signed range is poisoned, poisoned ranges are propagated
+  /// through the DAG and will cause the immediate UB if reached the
+  /// side-effecting operation.
+  bool isSignedPoison() const;
+
+  /// Returns true if unsigned range is poisoned, poisoned ranges are propagated
+  /// through the DAG and will cause the immediate UB if reached the
+  /// side-effecting operation.
+  bool isUnsignedPoison() const;
+
   friend raw_ostream &operator<<(raw_ostream &os,
                                  const ConstantIntRanges &range);
 
@@ -181,6 +198,7 @@ void defaultInferResultRanges(InferIntRangeInterface interface,
 void defaultInferResultRangesFromOptional(InferIntRangeInterface interface,
                                           ArrayRef<ConstantIntRanges> argRanges,
                                           SetIntRangeFn setResultRanges);
+
 } // end namespace intrange::detail
 } // end namespace mlir
 

mlir/include/mlir/Interfaces/InferIntRangeInterface.td

@@ -33,6 +33,9 @@ def InferIntRangeInterface : OpInterface<"InferIntRangeInterface"> {
       When operations take non-integer inputs, the
      `inferResultRangesFromOptional` method should be implemented instead.
 
+      If any of the operands have poison ranges, they will be propagated to the
+      results automatically after the metdod returns.
+
       When called on an op that also implements the RegionBranchOpInterface
       or BranchOpInterface, this method should not attempt to infer the values
       of the branch results, as this will be handled by the analyses that use
@@ -60,6 +63,10 @@ def InferIntRangeInterface : OpInterface<"InferIntRangeInterface"> {
       as an argument. When implemented, `setValueRange` should be called on
       all result values for the operation.
 
+      Unlike `inferResultRanges` this method does not automatically propagate
+      poison from the inputs. This allows more precise poison semantics
+      control.
+
       This method allows for more precise implementations when operations
       want to reason about inputs which may be undefined during the analysis.
     }],

mlir/lib/Dialect/Arith/Transforms/IntRangeOptimizations.cpp

@@ -15,6 +15,7 @@
 #include "mlir/Analysis/DataFlow/DeadCodeAnalysis.h"
 #include "mlir/Analysis/DataFlow/IntegerRangeAnalysis.h"
 #include "mlir/Dialect/Arith/IR/Arith.h"
+#include "mlir/Dialect/UB/IR/UBOps.h"
 #include "mlir/Dialect/Utils/StaticValueUtils.h"
 #include "mlir/IR/IRMapping.h"
 #include "mlir/IR/Matchers.h"
@@ -47,6 +48,19 @@ static std::optional<APInt> getMaybeConstantValue(DataFlowSolver &solver,
   return inferredRange.getConstantValue();
 }
 
+static bool isPoison(DataFlowSolver &solver, Value value) {
+  auto *maybeInferredRange =
+      solver.lookupState<IntegerValueRangeLattice>(value);
+  if (!maybeInferredRange || maybeInferredRange->getValue().isUninitialized())
+    return false;
+  const ConstantIntRanges &inferredRange =
+      maybeInferredRange->getValue().getValue();
+
+  // Only generate poison if both signed and unsigned ranges are guranteed to be
+  // poison.
+  return inferredRange.isSignedPoison() && inferredRange.isUnsignedPoison();
+}
+
 static void copyIntegerRange(DataFlowSolver &solver, Value oldVal,
                              Value newVal) {
   assert(oldVal.getType() == newVal.getType() &&
@@ -64,6 +78,17 @@ LogicalResult maybeReplaceWithConstant(DataFlowSolver &solver,
                                        RewriterBase &rewriter, Value value) {
   if (value.use_empty())
     return failure();
+
+  if (isPoison(solver, value)) {
+    Value poison =
+        ub::PoisonOp::create(rewriter, value.getLoc(), value.getType());
+    if (solver.lookupState<dataflow::IntegerValueRangeLattice>(poison))
+      solver.eraseState(poison);
+    copyIntegerRange(solver, value, poison);
+    rewriter.replaceAllUsesWith(value, poison);
+    return success();
+  }
+
   std::optional<APInt> maybeConstValue = getMaybeConstantValue(solver, value);
   if (!maybeConstValue.has_value())
     return failure();
@@ -132,7 +157,8 @@ struct MaterializeKnownConstantValues : public RewritePattern {
       return failure();
 
     auto needsReplacing = [&](Value v) {
-      return getMaybeConstantValue(solver, v).has_value() && !v.use_empty();
+      return (getMaybeConstantValue(solver, v) || isPoison(solver, v)) &&
+             !v.use_empty();
     };
     bool hasConstantResults = llvm::any_of(op->getResults(), needsReplacing);
     if (op->getNumRegions() == 0)

mlir/lib/Dialect/UB/IR/UBOps.cpp

@@ -59,6 +59,12 @@ Operation *UBDialect::materializeConstant(OpBuilder &builder, Attribute value,
 
 OpFoldResult PoisonOp::fold(FoldAdaptor /*adaptor*/) { return getValue(); }
 
+void PoisonOp::inferResultRanges(ArrayRef<ConstantIntRanges> /*argRanges*/,
+                                 SetIntRangeFn setResultRange) {
+  unsigned width = ConstantIntRanges::getStorageBitwidth(getType());
+  setResultRange(getResult(), ConstantIntRanges::poison(width));
+}
+
 #include "mlir/Dialect/UB/IR/UBOpsInterfaces.cpp.inc"
 
 #define GET_ATTRDEF_CLASSES

mlir/lib/Dialect/Vector/IR/VectorOps.cpp

@@ -3211,9 +3211,14 @@ void ShuffleOp::getCanonicalizationPatterns(RewritePatternSet &results,
 // InsertOp
 //===----------------------------------------------------------------------===//
 
-void vector::InsertOp::inferResultRanges(ArrayRef<ConstantIntRanges> argRanges,
-                                         SetIntRangeFn setResultRanges) {
-  setResultRanges(getResult(), argRanges[0].rangeUnion(argRanges[1]));
+void vector::InsertOp::inferResultRangesFromOptional(
+    ArrayRef<IntegerValueRange> argRanges, SetIntLatticeFn setResultRanges) {
+  if (argRanges[0].isUninitialized() || argRanges[1].isUninitialized())
+    return;
+
+  const ConstantIntRanges &range0 = argRanges[0].getValue();
+  const ConstantIntRanges &range1 = argRanges[1].getValue();
+  setResultRanges(getResult(), range0.rangeUnion(range1));
 }
 
 void vector::InsertOp::build(OpBuilder &builder, OperationState &result,

mlir/lib/Interfaces/InferIntRangeInterface.cpp

@@ -28,6 +28,8 @@ const APInt &ConstantIntRanges::smin() const { return sminVal; }
 
 const APInt &ConstantIntRanges::smax() const { return smaxVal; }
 
+unsigned ConstantIntRanges::getBitWidth() const { return umin().getBitWidth(); }
+
 unsigned ConstantIntRanges::getStorageBitwidth(Type type) {
   type = getElementTypeOrSelf(type);
   if (type.isIndex())
@@ -42,6 +44,21 @@ ConstantIntRanges ConstantIntRanges::maxRange(unsigned bitwidth) {
   return fromUnsigned(APInt::getZero(bitwidth), APInt::getMaxValue(bitwidth));
 }
 
+ConstantIntRanges ConstantIntRanges::poison(unsigned bitwidth) {
+  if (bitwidth == 0) {
+    auto zero = APInt::getZero(0);
+    return {zero, zero, zero, zero};
+  }
+
+  // Poison is represented by an empty range.
+  auto zero = APInt::getZero(bitwidth);
+  auto one = zero + 1;
+  auto onem = zero - 1;
+  // For i1 the valid unsigned range is [0, 1] and the valid signed range
+  // is [-1, 0].
+  return {one, zero, zero, onem};
+}
+
 ConstantIntRanges ConstantIntRanges::constant(const APInt &value) {
   return {value, value, value, value};
 }
@@ -85,15 +102,44 @@ ConstantIntRanges
 ConstantIntRanges::rangeUnion(const ConstantIntRanges &other) const {
   // "Not an integer" poisons everything and also cannot be fed to comparison
   // operators.
-  if (umin().getBitWidth() == 0)
+  if (getBitWidth() == 0)
     return *this;
-  if (other.umin().getBitWidth() == 0)
+  if (other.getBitWidth() == 0)
     return other;
 
-  const APInt &uminUnion = umin().ult(other.umin()) ? umin() : other.umin();
-  const APInt &umaxUnion = umax().ugt(other.umax()) ? umax() : other.umax();
-  const APInt &sminUnion = smin().slt(other.smin()) ? smin() : other.smin();
-  const APInt &smaxUnion = smax().sgt(other.smax()) ? smax() : other.smax();
+  APInt uminUnion;
+  APInt umaxUnion;
+  APInt sminUnion;
+  APInt smaxUnion;
+
+  // Union of poisoned range with any other range is the other range.
+  // Union is used when we need to merge ranges from multiple indepdenent
+  // sources, e.g. in `arith.select` or CFG merge. "Observing" a poisoned
+  // value (using it in side-effecting operation) will cause the immediate UB.
+  // Well-formed programs should never observe the immediate UB so we assume
+  // result is either unused or only used in circumstances when it received the
+  // non-poisoned argument.
+  if (isUnsignedPoison()) {
+    uminUnion = other.umin();
+    umaxUnion = other.umax();
+  } else if (other.isUnsignedPoison()) {
+    uminUnion = umin();
+    umaxUnion = umax();
+  } else {
+    uminUnion = umin().ult(other.umin()) ? umin() : other.umin();
+    umaxUnion = umax().ugt(other.umax()) ? umax() : other.umax();
+  }
+
+  if (isSignedPoison()) {
+    sminUnion = other.smin();
+    smaxUnion = other.smax();
+  } else if (other.isSignedPoison()) {
+    sminUnion = smin();
+    smaxUnion = smax();
+  } else {
+    sminUnion = smin().slt(other.smin()) ? smin() : other.smin();
+    smaxUnion = smax().sgt(other.smax()) ? smax() : other.smax();
+  }
 
   return {uminUnion, umaxUnion, sminUnion, smaxUnion};
 }
@@ -102,15 +148,38 @@ ConstantIntRanges
 ConstantIntRanges::intersection(const ConstantIntRanges &other) const {
   // "Not an integer" poisons everything and also cannot be fed to comparison
   // operators.
-  if (umin().getBitWidth() == 0)
+  if (getBitWidth() == 0)
     return *this;
-  if (other.umin().getBitWidth() == 0)
+  if (other.getBitWidth() == 0)
     return other;
 
-  const APInt &uminIntersect = umin().ugt(other.umin()) ? umin() : other.umin();
-  const APInt &umaxIntersect = umax().ult(other.umax()) ? umax() : other.umax();
-  const APInt &sminIntersect = smin().sgt(other.smin()) ? smin() : other.smin();
-  const APInt &smaxIntersect = smax().slt(other.smax()) ? smax() : other.smax();
+  APInt uminIntersect;
+  APInt umaxIntersect;
+  APInt sminIntersect;
+  APInt smaxIntersect;
+
+  // Intersection of poisoned range with any other range is poisoned.
+  if (isUnsignedPoison()) {
+    uminIntersect = umin();
+    umaxIntersect = umax();
+  } else if (other.isUnsignedPoison()) {
+    uminIntersect = other.umin();
+    umaxIntersect = other.umax();
+  } else {
+    uminIntersect = umin().ugt(other.umin()) ? umin() : other.umin();
+    umaxIntersect = umax().ult(other.umax()) ? umax() : other.umax();
+  }
+
+  if (isSignedPoison()) {
+    sminIntersect = smin();
+    smaxIntersect = smax();
+  } else if (other.isSignedPoison()) {
+    sminIntersect = other.smin();
+    smaxIntersect = other.smax();
+  } else {
+    sminIntersect = smin().sgt(other.smin()) ? smin() : other.smin();
+    smaxIntersect = smax().slt(other.smax()) ? smax() : other.smax();
+  }
 
   return {uminIntersect, umaxIntersect, sminIntersect, smaxIntersect};
 }
@@ -124,6 +193,14 @@ std::optional<APInt> ConstantIntRanges::getConstantValue() const {
   return std::nullopt;
 }
 
+bool ConstantIntRanges::isSignedPoison() const {
+  return getBitWidth() > 0 && smin().sgt(smax());
+}
+
+bool ConstantIntRanges::isUnsignedPoison() const {
+  return getBitWidth() > 0 && umin().ugt(umax());
+}
+
 raw_ostream &mlir::operator<<(raw_ostream &os, const ConstantIntRanges &range) {
   os << "unsigned : [";
   range.umin().print(os, /*isSigned*/ false);
@@ -152,17 +229,32 @@ void mlir::intrange::detail::defaultInferResultRanges(
   llvm::SmallVector<ConstantIntRanges> unpacked;
   unpacked.reserve(argRanges.size());
 
+  bool signedPoison = false;
+  bool unsignedPoison = false;
   for (const IntegerValueRange &range : argRanges) {
     if (range.isUninitialized())
       return;
-    unpacked.push_back(range.getValue());
+
+    const ConstantIntRanges &value = range.getValue();
+    unpacked.push_back(value);
+    signedPoison = signedPoison || value.isSignedPoison();
+    unsignedPoison = unsignedPoison || value.isUnsignedPoison();
   }
 
-  interface.inferResultRanges(
-      unpacked,
-      [&setResultRanges](Value value, const ConstantIntRanges &argRanges) {
-        setResultRanges(value, IntegerValueRange{argRanges});
-      });
+  auto visitor = [&](Value value, const ConstantIntRanges &range) {
+    if (!signedPoison && !unsignedPoison)
+      return setResultRanges(value, range);
+
+    auto poison = ConstantIntRanges::poison(range.getBitWidth());
+    APInt umin = unsignedPoison ? poison.umin() : range.umin();
+    APInt umax = unsignedPoison ? poison.umax() : range.umax();
+    APInt smin = signedPoison ? poison.smin() : range.smin();
+    APInt smax = signedPoison ? poison.smax() : range.smax();
+
+    setResultRanges(value, ConstantIntRanges(umin, umax, smin, smax));
+  };
+
+  interface.inferResultRanges(unpacked, visitor);
 }
 
 void mlir::intrange::detail::defaultInferResultRangesFromOptional(