[ConstantRangeTest] Print detailed information on failure (NFC)

When the optimality check fails, print the inputs, the computed
range and the better range that was found. This makes it much
simpler to identify the cause of the failure.

Make sure that full ranges (which, unlikely all the other cases,
have multiple ways to construct them that all result in the same
range) only print one message by handling them separately.

llvm/unittests/IR/ConstantRangeTest.cpp

@@ -94,11 +94,13 @@ bool PreferSmallestNonFullSigned(const ConstantRange &CR1,
   return PreferSmallestSigned(CR1, CR2);
 }
 
+
+
 // Check whether constant range CR is an optimal approximation of the set
 // Elems under the given PreferenceFn. The preference function should return
 // true if the first range argument is strictly preferred to the second one.
 static void TestRange(const ConstantRange &CR, const SmallBitVector &Elems,
-                      PreferFn PreferenceFn) {
+                      PreferFn PreferenceFn, ArrayRef<ConstantRange> Inputs) {
   unsigned BitWidth = CR.getBitWidth();
 
   // Check conservative correctness.
@@ -106,16 +108,23 @@ static void TestRange(const ConstantRange &CR, const SmallBitVector &Elems,
     EXPECT_TRUE(CR.contains(APInt(BitWidth, Elem)));
   }
 
-  // Make sure we have at least two elements for the code below.
+  // Make sure we have at least one element for the code below.
   if (Elems.none()) {
     EXPECT_TRUE(CR.isEmptySet());
     return;
   }
 
-  if (Elems.count() == 1) {
-    EXPECT_TRUE(CR.isSingleElement());
-    return;
-  }
+  auto NotPreferred = [&](const ConstantRange &PossibleCR) {
+    if (!PreferenceFn(PossibleCR, CR))
+      return testing::AssertionSuccess();
+
+    testing::AssertionResult Result = testing::AssertionFailure();
+    Result << "Inputs = ";
+    for (const ConstantRange &Input : Inputs)
+      Result << Input << ", ";
+    Result << "CR = " << CR << ", BetterCR = " << PossibleCR;
+    return Result;
+  };
 
   // Look at all pairs of adjacent elements and the slack-free ranges
   // [Elem, PrevElem] they imply. Check that none of the ranges are strictly
@@ -130,12 +139,16 @@ static void TestRange(const ConstantRange &CR, const SmallBitVector &Elems,
     ConstantRange PossibleCR =
         ConstantRange::getNonEmpty(APInt(BitWidth, Elem),
                                    APInt(BitWidth, PrevElem) + 1);
-    // There should be no range that is preferred over CR.
-    EXPECT_FALSE(PreferenceFn(PossibleCR, CR))
-      << "CR = " << CR << ", BetterCR = " << PossibleCR;
+    // We get a full range any time PrevElem and Elem are adjacent. Avoid
+    // repeated checks by skipping here, and explicitly checking below instead.
+    if (!PossibleCR.isFullSet()) {
+      EXPECT_TRUE(NotPreferred(PossibleCR));
+    }
 
     PrevElem = Elem;
   } while (Elem != FirstElem);
+
+  EXPECT_TRUE(NotPreferred(ConstantRange::getFull(BitWidth)));
 }
 
 using UnaryRangeFn = llvm::function_ref<ConstantRange(const ConstantRange &)>;
@@ -150,7 +163,7 @@ static void TestUnaryOpExhaustive(UnaryRangeFn RangeFn, UnaryIntFn IntFn,
       if (Optional<APInt> ResultN = IntFn(N))
         Elems.set(ResultN->getZExtValue());
     });
-    TestRange(RangeFn(CR), Elems, PreferenceFn);
+    TestRange(RangeFn(CR), Elems, PreferenceFn, {CR});
   });
 }
 
@@ -171,7 +184,7 @@ static void TestBinaryOpExhaustive(BinaryRangeFn RangeFn, BinaryIntFn IntFn,
               Elems.set(ResultN->getZExtValue());
           });
         });
-        TestRange(RangeFn(CR1, CR2), Elems, PreferenceFn);
+        TestRange(RangeFn(CR1, CR2), Elems, PreferenceFn, {CR1, CR2});
       });
 }
 
@@ -543,13 +556,13 @@ void testBinarySetOperationExhaustive(Fn1 OpFn, Fn2 InResultFn) {
             Elems.set(Num.getZExtValue());
 
         ConstantRange SmallestCR = OpFn(CR1, CR2, ConstantRange::Smallest);
-        TestRange(SmallestCR, Elems, PreferSmallest);
+        TestRange(SmallestCR, Elems, PreferSmallest, {CR1, CR2});
 
         ConstantRange UnsignedCR = OpFn(CR1, CR2, ConstantRange::Unsigned);
-        TestRange(UnsignedCR, Elems, PreferSmallestNonFullUnsigned);
+        TestRange(UnsignedCR, Elems, PreferSmallestNonFullUnsigned, {CR1, CR2});
 
         ConstantRange SignedCR = OpFn(CR1, CR2, ConstantRange::Signed);
-        TestRange(SignedCR, Elems, PreferSmallestNonFullSigned);
+        TestRange(SignedCR, Elems, PreferSmallestNonFullSigned, {CR1, CR2});
       });
 }