[ConstantRange] Add makeExactNoWrapRegion()

I got confused on the terminology, and the change in D60598 was not
correct. I was thinking of "exact" in terms of the result being
non-approximate. However, the relevant distinction here is whether
the result is

 * Largest range such that:
   Forall Y in Other: Forall X in Result: X BinOp Y does not wrap.
   (makeGuaranteedNoWrapRegion)
 * Smallest range such that:
   Forall Y in Other: Forall X not in Result: X BinOp Y wraps.
   (A hypothetical makeAllowedNoWrapRegion)
 * Both. (makeExactNoWrapRegion)

I'm adding a separate makeExactNoWrapRegion method accepting a
single APInt (same as makeExactICmpRegion) and using it in the
places where the guarantee is relevant.

Differential Revision: https://reviews.llvm.org/D60960

llvm-svn: 359402

include/llvm/IR/ConstantRange.h

@@ -124,8 +124,10 @@ public:
   static ConstantRange makeExactICmpRegion(CmpInst::Predicate Pred,
                                            const APInt &Other);
 
-  /// Return the exact range containing all X such that "X BinOpC Y" is
-  /// guaranteed not to wrap (overflow) for all Y in Other.
+  /// Produce the largest range containing all X such that "X BinOp Y" is
+  /// guaranteed not to wrap (overflow) for *all* Y in Other. However, there may
+  /// be *some* Y in Other for which additional X not contained in the result
+  /// also do not overflow.
   ///
   /// NoWrapKind must be one of OBO::NoUnsignedWrap or OBO::NoSignedWrap.
   ///
@@ -142,6 +144,12 @@ public:
                                                   const ConstantRange &Other,
                                                   unsigned NoWrapKind);
 
+  /// Produce the range that contains X if and only if "X BinOp Other" does
+  /// not wrap.
+  static ConstantRange makeExactNoWrapRegion(Instruction::BinaryOps BinOp,
+                                             const APInt &Other,
+                                             unsigned NoWrapKind);
+
   /// Set up \p Pred and \p RHS such that
   /// ConstantRange::makeExactICmpRegion(Pred, RHS) == *this.  Return true if
   /// successful.

lib/Analysis/LazyValueInfo.cpp

@@ -1146,8 +1146,8 @@ static ValueLatticeElement getValueFromOverflowCondition(
     return ValueLatticeElement::getOverdefined();
 
   // Calculate the possible values of %x for which no overflow occurs.
-  ConstantRange NWR = ConstantRange::makeGuaranteedNoWrapRegion(
-      WO->getBinaryOp(), ConstantRange(*C), WO->getNoWrapKind());
+  ConstantRange NWR = ConstantRange::makeExactNoWrapRegion(
+      WO->getBinaryOp(), *C, WO->getNoWrapKind());
 
   // If overflow is false, %x is constrained to NWR. If overflow is true, %x is
   // constrained to it's inverse (all values that might cause overflow).

lib/IR/ConstantRange.cpp

@@ -309,6 +309,14 @@ ConstantRange::makeGuaranteedNoWrapRegion(Instruction::BinaryOps BinOp,
   }
 }
 
+ConstantRange ConstantRange::makeExactNoWrapRegion(Instruction::BinaryOps BinOp,
+                                                   const APInt &Other,
+                                                   unsigned NoWrapKind) {
+  // makeGuaranteedNoWrapRegion() is exact for single-element ranges, as
+  // "for all" and "for any" coincide in this case.
+  return makeGuaranteedNoWrapRegion(BinOp, ConstantRange(Other), NoWrapKind);
+}
+
 bool ConstantRange::isFullSet() const {
   return Lower == Upper && Lower.isMaxValue();
 }
@@ -843,10 +851,8 @@ ConstantRange::add(const ConstantRange &Other) const {
 ConstantRange ConstantRange::addWithNoSignedWrap(const APInt &Other) const {
   // Calculate the subset of this range such that "X + Other" is
   // guaranteed not to wrap (overflow) for all X in this subset.
-  // makeGuaranteedNoWrapRegion will produce an exact NSW range.
-  auto NSWRange = ConstantRange::makeGuaranteedNoWrapRegion(BinaryOperator::Add,
-                                      ConstantRange(Other),
-                                      OverflowingBinaryOperator::NoSignedWrap);
+  auto NSWRange = ConstantRange::makeExactNoWrapRegion(
+      BinaryOperator::Add, Other, OverflowingBinaryOperator::NoSignedWrap);
   auto NSWConstrainedRange = intersectWith(NSWRange);
 
   return NSWConstrainedRange.add(ConstantRange(Other));

unittests/IR/ConstantRangeTest.cpp

@@ -1176,17 +1176,25 @@ void TestNoWrapRegionExhaustive(Instruction::BinaryOps BinOp,
             ConstantRange::makeGuaranteedNoWrapRegion(BinOp, CR2, NoWrapKind);
         ForeachNumInConstantRange(CR1, [&](const APInt &N1) {
           bool NoOverflow = true;
+          bool Overflow = true;
           ForeachNumInConstantRange(CR2, [&](const APInt &N2) {
             if (OverflowFn(N1, N2))
               NoOverflow = false;
+            else
+              Overflow = false;
           });
           EXPECT_EQ(NoOverflow, NoWrap.contains(N1));
+
+          // The no-wrap range is exact for single-element ranges.
+          if (CR2.isSingleElement()) {
+            EXPECT_EQ(Overflow, !NoWrap.contains(N1));
+          }
         });
       });
 }
 
-// Show that makeGuaranteedNoWrapRegion is precise if only one of
-// NoUnsignedWrap or NoSignedWrap is used.
+// Show that makeGuaranteedNoWrapRegion() is maximal, and for single-element
+// ranges also exact.
 TEST(ConstantRange, NoWrapRegionExhaustive) {
   TestNoWrapRegionExhaustive(
       Instruction::Add, OverflowingBinaryOperator::NoUnsignedWrap,