Initial implementation of ConstantRange support

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@3563 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Analysis/ConstantRange.cpp

@@ -0,0 +1,227 @@
+//===-- ConstantRange.cpp - ConstantRange implementation ------------------===//
+//
+// Represent a range of possible values that may occur when the program is run
+// for an integral value.  This keeps track of a lower and upper bound for the
+// constant, which MAY wrap around the end of the numeric range.  To do this, it
+// keeps track of a [lower, upper) bound, which specifies an interval just like
+// STL iterators.  When used with boolean values, the following are important
+// ranges (other integral ranges use min/max values for special range values):
+//
+//  [F, F) = {}     = Empty set
+//  [T, F) = {T}
+//  [F, T) = {F}
+//  [T, T) = {F, T} = Full set
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/ConstantRange.h"
+#include "llvm/Type.h"
+#include "llvm/Instruction.h"
+#include "llvm/ConstantHandling.h"
+
+/// Initialize a full (the default) or empty set for the specified type.
+///
+ConstantRange::ConstantRange(const Type *Ty, bool Full) {
+  assert(Ty->isIntegral() &&
+         "Cannot make constant range of non-integral type!");
+  if (Full)
+    Lower = Upper = ConstantIntegral::getMaxValue(Ty);
+  else
+    Lower = Upper = ConstantIntegral::getMinValue(Ty);
+}
+
+/// Initialize a range of values explicitly... this will assert out if
+/// Lower==Upper and Lower != Min or Max for its type (or if the two constants
+/// have different types)
+///
+ConstantRange::ConstantRange(ConstantIntegral *L,
+                             ConstantIntegral *U) : Lower(L), Upper(U) {
+  assert(Lower->getType() == Upper->getType() &&
+         "Incompatible types for ConstantRange!");
+
+  // Make sure that if L & U are equal that they are either Min or Max...
+  assert((L != U || (L == ConstantIntegral::getMaxValue(L->getType()) ||
+                     L == ConstantIntegral::getMinValue(L->getType()))) &&
+         "Lower == Upper, but they aren't min or max for type!");
+}
+
+static ConstantIntegral *Next(ConstantIntegral *CI) {
+  if (CI->getType() == Type::BoolTy)
+    return CI == ConstantBool::True ? ConstantBool::False : ConstantBool::True;
+
+  // Otherwise use operator+ in the ConstantHandling Library.
+  Constant *Result = *ConstantInt::get(CI->getType(), 1) + *CI;
+  assert(Result && "ConstantHandling not implemented for integral plus!?");
+  return cast<ConstantIntegral>(Result);
+}
+
+/// Initialize a set of values that all satisfy the condition with C.
+///
+ConstantRange::ConstantRange(unsigned SetCCOpcode, ConstantIntegral *C) {
+  switch (SetCCOpcode) {
+  default: assert(0 && "Invalid SetCC opcode to ConstantRange ctor!");
+  case Instruction::SetEQ: Lower = C; Upper = Next(C); return;
+  case Instruction::SetNE: Upper = C; Lower = Next(C); return;
+  case Instruction::SetLT:
+    Lower = ConstantIntegral::getMinValue(C->getType());
+    Upper = C;
+    return;
+  case Instruction::SetGT:
+    Upper = ConstantIntegral::getMaxValue(C->getType());
+    Lower = Next(C);
+    return;
+  case Instruction::SetLE:
+    Lower = ConstantIntegral::getMinValue(C->getType());
+    Upper = Next(C);
+    return;
+  case Instruction::SetGE:
+    Upper = ConstantIntegral::getMaxValue(C->getType());
+    Lower = C;
+    return;
+  }
+}
+
+/// getType - Return the LLVM data type of this range.
+///
+const Type *ConstantRange::getType() const { return Lower->getType(); }
+
+/// isFullSet - Return true if this set contains all of the elements possible
+/// for this data-type
+bool ConstantRange::isFullSet() const {
+  return Lower == Upper && Lower == ConstantIntegral::getMaxValue(getType());
+}
+
+/// isEmptySet - Return true if this set contains no members.
+///
+bool ConstantRange::isEmptySet() const {
+  return Lower == Upper && Lower == ConstantIntegral::getMinValue(getType());
+}
+
+/// isWrappedSet - Return true if this set wraps around the top of the range,
+/// for example: [100, 8)
+///
+bool ConstantRange::isWrappedSet() const {
+  return (*(Constant*)Lower > *(Constant*)Upper)->getValue();
+}
+
+
+/// getSingleElement - If this set contains a single element, return it,
+/// otherwise return null.
+ConstantIntegral *ConstantRange::getSingleElement() const {
+  if (Upper == Next(Lower))  // Is it a single element range?
+    return Lower;
+  return 0;
+}
+
+/// getSetSize - Return the number of elements in this set.
+///
+uint64_t ConstantRange::getSetSize() const {
+  if (isEmptySet()) return 0;
+  if (getType() == Type::BoolTy) {
+    if (Lower != Upper)  // One of T or F in the set...
+      return 1;
+    return 2;            // Must be full set...
+  }
+
+  // Simply subtract the bounds...
+  Constant *Result = *(Constant*)Upper - *(Constant*)Lower;
+  assert(Result && "Subtraction of constant integers not implemented?");
+  if (getType()->isSigned())
+    return (uint64_t)cast<ConstantSInt>(Result)->getValue();
+  else
+    return cast<ConstantUInt>(Result)->getValue();
+}
+
+
+
+
+// intersect1Wrapped - This helper function is used to intersect two ranges when
+// it is known that LHS is wrapped and RHS isn't.
+//
+static ConstantRange intersect1Wrapped(const ConstantRange &LHS,
+                                       const ConstantRange &RHS) {
+  assert(LHS.isWrappedSet() && !RHS.isWrappedSet());
+
+  // Handle common special cases
+  if (RHS.isEmptySet()) return RHS;
+  if (RHS.isFullSet()) return LHS;
+
+  // Check to see if we overlap on the Left side of RHS...
+  //
+  if ((*(Constant*)RHS.getLower() < *(Constant*)LHS.getUpper())->getValue()) {
+    // We do overlap on the left side of RHS, see if we overlap on the right of
+    // RHS...
+    if ((*(Constant*)RHS.getUpper() > *(Constant*)LHS.getLower())->getValue()) {
+      // Ok, the result overlaps on both the left and right sides.  See if the
+      // resultant interval will be smaller if we wrap or not...
+      //
+      if (LHS.getSetSize() < RHS.getSetSize())
+        return LHS;
+      else
+        return RHS;
+
+    } else {
+      // No overlap on the right, just on the left.
+      return ConstantRange(RHS.getLower(), LHS.getUpper());
+    }
+
+  } else {
+    // We don't overlap on the left side of RHS, see if we overlap on the right
+    // of RHS...
+    if ((*(Constant*)RHS.getUpper() > *(Constant*)LHS.getLower())->getValue()) {
+      // Simple overlap...
+      return ConstantRange(LHS.getLower(), RHS.getUpper());
+    } else {
+      // No overlap...
+      return ConstantRange(LHS.getType(), false);
+    }
+  }
+}
+
+
+/// intersect - Return the range that results from the intersection of this
+/// range with another range.
+///
+ConstantRange ConstantRange::intersectWith(const ConstantRange &CR) const {
+  assert(getType() == CR.getType() && "ConstantRange types don't agree!");
+
+  if (!isWrappedSet()) {
+    if (!CR.isWrappedSet()) {
+      const Constant &L = std::max(*(Constant*)Lower, *(Constant*)CR.Lower);
+      const Constant &U = std::min(*(Constant*)Upper, *(Constant*)CR.Upper);
+
+      if ((L < U)->getValue())  // If range isn't empty...
+        return ConstantRange(cast<ConstantIntegral>((Constant*)&L),
+                             cast<ConstantIntegral>((Constant*)&U));
+      else
+        return ConstantRange(getType(), false);  // Otherwise, return empty set
+    } else
+      return intersect1Wrapped(CR, *this);
+  } else {   // We know "this" is wrapped...
+    if (!CR.isWrappedSet())
+      return intersect1Wrapped(*this, CR);
+    else {
+      // Both ranges are wrapped...
+      const Constant &L = std::max(*(Constant*)Lower, *(Constant*)CR.Lower);
+      const Constant &U = std::min(*(Constant*)Upper, *(Constant*)CR.Upper);
+
+      return ConstantRange(cast<ConstantIntegral>((Constant*)&L),
+                           cast<ConstantIntegral>((Constant*)&U));      
+    }
+  }
+  return *this;
+}
+
+/// union - Return the range that results from the union of this range with
+/// another range.  The resultant range is guaranteed to include the elements of
+/// both sets, but may contain more.  For example, [3, 9) union [12,15) is [3,
+/// 15), which includes 9, 10, and 11, which were not included in either set
+/// before.
+///
+ConstantRange ConstantRange::unionWith(const ConstantRange &CR) const {
+  assert(getType() == CR.getType() && "ConstantRange types don't agree!");
+
+  assert(0 && "Range union not implemented yet!");
+
+  return *this;
+}