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

Author: Hardcode84

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 "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/Interfaces/InferIntRangeInterface.h

@@ -62,6 +62,10 @@ class ConstantIntRanges {
   /// sint_max(width)].
   static ConstantIntRanges maxRange(unsigned bitwidth);
 
+  /// Create a poisoned range, i.e. a range that represents no valid integer
+  /// values.
+  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 +100,14 @@ class ConstantIntRanges {
   /// value.
   std::optional<APInt> getConstantValue() const;
 
+  /// Returns true if signed range is poisoned, i.e. no valid signed value
+  /// can be represented.
+  bool isSignedPoison() const;
+
+  /// Returns true if unsigned range is poisoned, i.e. no valid unsigned value
+  /// can be represented.
+  bool isUnsignedPoison() const;
+
   friend raw_ostream &operator<<(raw_ostream &os,
                                  const ConstantIntRanges &range);
 

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/Interfaces/InferIntRangeInterface.cpp

@@ -42,6 +42,16 @@ ConstantIntRanges ConstantIntRanges::maxRange(unsigned bitwidth) {
   return fromUnsigned(APInt::getZero(bitwidth), APInt::getMaxValue(bitwidth));
 }
 
+ConstantIntRanges ConstantIntRanges::poison(unsigned bitwidth) {
+  if (bitwidth == 0)
+    return maxRange(0);
+
+  // Poison is represented by an empty range.
+  auto max = APInt::getZero(bitwidth);
+  auto min = max + 1;
+  return {min, max, min, max};
+}
+
 ConstantIntRanges ConstantIntRanges::constant(const APInt &value) {
   return {value, value, value, value};
 }
@@ -90,10 +100,32 @@ ConstantIntRanges::rangeUnion(const ConstantIntRanges &other) const {
   if (other.umin().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;
+
+  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};
 }
@@ -107,10 +139,32 @@ ConstantIntRanges::intersection(const ConstantIntRanges &other) const {
   if (other.umin().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;
+
+  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 +178,10 @@ std::optional<APInt> ConstantIntRanges::getConstantValue() const {
   return std::nullopt;
 }
 
+bool ConstantIntRanges::isSignedPoison() const { return smin().sgt(smax()); }
+
+bool ConstantIntRanges::isUnsignedPoison() const { return umin().ugt(umax()); }
+
 raw_ostream &mlir::operator<<(raw_ostream &os, const ConstantIntRanges &range) {
   os << "unsigned : [";
   range.umin().print(os, /*isSigned*/ false);