[ValueLattice] Update markConstantRange to return false for subset ranges.

[fhahn]

Summary

Currently we always return true, when markConstantRange is used on an
object already containing a constant range. If NewR is equal to the
existing constant range however, nothing changes and we should return
false.

I also went ahead and added a clarifying comment and improved the
assertion.

[merge_guards_bot]

Unit tests: unknown.

clang-tidy: unknown.

clang-format: unknown.

Build artifacts: diff.json, console-log.txt

[efriedma]

llvm/include/llvm/Analysis/ValueLattice.h

229

If NewR is precisely equal to the current range, it makes sense to do nothing. It doesn't make sense to call markConstantRange with a NewR that's a subset of the current range.

[fhahn]

Restrict input for markConstantRange to either matching the existing constant range or being a superset.

[merge_guards_bot]

Unit tests: unknown.

clang-tidy: unknown.

clang-format: unknown.

Build artifacts: diff.json, console-log.txt

[fhahn]

llvm/include/llvm/Analysis/ValueLattice.h

229

Right, I've restricted the acceptable values of NewR and also updated the description.

[efriedma]

LGTM

llvm/include/llvm/Analysis/ValueLattice.h

bool markNotConstant(Constant *V) {
     }
 
     assert(isUndefined());
     Tag = notconstant;
     ConstVal = V;
     return true;
   }
 
+  /// Mark the object as constant range with \p NewR. If the object is already a
+  /// constant range, nothing changes if the existing range is equal to \p
+  /// NewR. Otherwise \p NewR must be a superset of the existing range or the
+  /// object must be undefined.
   bool markConstantRange(ConstantRange NewR) {
     if (isConstantRange()) {
+      if (getConstantRange() == NewR)
+        return false;
+
       if (NewR.isEmptySet())
-        markOverdefined();
-      else {
-        assert(NewR.contains(getConstantRange()) && "Existing range must be a subset of NewR");
-        Range = std::move(NewR);
-      }
+        return markOverdefined();
+
+      assert(NewR.contains(getConstantRange()) &&
+             "Existing range must be a subset of NewR");
       return true;
     }
 
     assert(isUndefined());
     if (NewR.isEmptySet())
       return markOverdefined();
 
     Tag = constantrange;

llvm/unittests/Analysis/ValueLatticeTest.cpp

TEST_F(ValueLatticeTest, ValueLatticeGetters) {
   EXPECT_TRUE(ValueLatticeElement::getOverdefined().isOverdefined());
 
   auto FloatTy = Type::getFloatTy(Context);
   auto *C2 = ConstantFP::get(FloatTy, 1.1);
   EXPECT_TRUE(ValueLatticeElement::get(C2).isConstant());
   EXPECT_TRUE(ValueLatticeElement::getNot(C2).isNotConstant());
 }
 
+TEST_F(ValueLatticeTest, MarkConstantRange) {
+  auto LV1 =
+      ValueLatticeElement::getRange({APInt(32, 10, true), APInt(32, 20, true)});
+
+  // Test markConstantRange() with an equal range.
+  EXPECT_FALSE(
+      LV1.markConstantRange({APInt(32, 10, true), APInt(32, 20, true)}));
+
+  // Test markConstantRange() with supersets of existing range.
+  EXPECT_TRUE(LV1.markConstantRange({APInt(32, 5, true), APInt(32, 20, true)}));
+  EXPECT_EQ(LV1.getConstantRange().getLower().getLimitedValue(), 5U);
+  EXPECT_EQ(LV1.getConstantRange().getUpper().getLimitedValue(), 20U);
+  EXPECT_TRUE(LV1.markConstantRange({APInt(32, 5, true), APInt(32, 23, true)}));
+  EXPECT_EQ(LV1.getConstantRange().getLower().getLimitedValue(), 5U);
+  EXPECT_EQ(LV1.getConstantRange().getUpper().getLimitedValue(), 23U);
+}
+
 TEST_F(ValueLatticeTest, MergeIn) {
   auto I32Ty = IntegerType::get(Context, 32);
   auto *C1 = ConstantInt::get(I32Ty, 1);
 
   // Merge to lattice values with equal integer constant.
   auto LV1 = ValueLatticeElement::get(C1);
   EXPECT_FALSE(LV1.mergeIn(ValueLatticeElement::get(C1), M.getDataLayout()));
   EXPECT_TRUE(LV1.isConstantRange());