Add C++ shape inference for SVD.

This also adds Min(), Max(), and Subtract() operators and a few convenience methods to the InferenceContext. Change test utils to emit a human readable error message in case the user forgot to set the inference function.

Refactored shape_inference* a bit to enforce the invariant that a Dimension or DimensionOrConstant is always non-negative or equal to InferenceContext::kUnknownDim.
This made it possible to tighten & simplify the arithmetic operations a bit.
Change: 129385995

4 files changed, 320 insertions, 107 deletions

diff --git a/tensorflow/core/framework/shape_inference.cc b/tensorflow/core/framework/shape_inference.cc
index e44d921d5d..9c90bfe0f5 100644
--- a/tensorflow/core/framework/shape_inference.cc
+++ b/tensorflow/core/framework/shape_inference.cc
@@ -387,12 +387,6 @@ Status InferenceContext::ReplaceDim(const Shape* s, int dim_index_in,
   return ReturnCreatedShape(dims, out);
 }
 
-const Dimension* InferenceContext::GetDimension(const DimensionOrConstant& d) {
-  if (d.dim != nullptr) return d.dim;
-  DCHECK(d.val >= 0 || d.val == kUnknownDim);
-  return MakeDim(d.val);
-}
-
 const Shape* InferenceContext::MakeShape(
     const std::vector<const Dimension*>& dims) {
   all_shapes_.push_back(new Shape(dims));
@@ -404,7 +398,7 @@ const Shape* InferenceContext::MakeShape(
   std::vector<const Dimension*> dims_actual;
   dims_actual.reserve(dims.size());
   for (const DimensionOrConstant& d : dims) {
-    dims_actual.push_back(GetDimension(d));
+    dims_actual.push_back(MakeDim(d));
   }
   return MakeShape(dims_actual);
 }
@@ -488,11 +482,6 @@ Status InferenceContext::MakeShapeFromShapeProto(const TensorShapeProto& proto,
   return ReturnCreatedShape(dims, out);
 }
 
-const Dimension* InferenceContext::MakeDim(int64 value) {
-  all_dims_.push_back(new Dimension(value));
-  return all_dims_.back();
-}
-
 // Returns a new dimension whose value is given by a scalar input tensor.
 Status InferenceContext::MakeDimForScalarInput(int idx, const Dimension** out) {
   const Tensor* t = input_tensor(idx);
@@ -522,11 +511,6 @@ Status InferenceContext::MakeDimForScalarInput(int idx, const Dimension** out) {
   return Status::OK();
 }
 
-const Dimension* InferenceContext::UnknownDim() {
-  all_dims_.push_back(new Dimension());
-  return all_dims_.back();
-}
-
 Status InferenceContext::Divide(const Dimension* dividend, int64 divisor,
                                 const Dimension** out) {
   if (divisor == 1) {
@@ -535,6 +519,10 @@ Status InferenceContext::Divide(const Dimension* dividend, int64 divisor,
     *out = UnknownDim();
   } else {
     const int64 v = Value(dividend);
+    if (divisor <= 0) {
+      return errors::InvalidArgument("Divisor must be positive but is ",
+                                     divisor);
+    }
     if ((v % divisor) != 0) {
       return errors::InvalidArgument("Dimension size must be divisible by ",
                                      divisor, " but is ", v);
@@ -546,87 +534,112 @@ Status InferenceContext::Divide(const Dimension* dividend, int64 divisor,
 
 Status InferenceContext::Add(const Dimension* first, DimensionOrConstant second,
                              const Dimension** out) {
-  const int64 second_value =
-      second.dim == nullptr ? second.val : Value(second.dim);
-  if (second.dim != nullptr && !ValueKnown(second.dim)) {
-    *out = UnknownDim();
+  const int64 first_value = Value(first);
+  const int64 second_value = Value(second);
+  // Special cases.
+  if (first_value == 0) {
+    *out = MakeDim(second);
   } else if (second_value == 0) {
-    *out = first;
-  } else if (!ValueKnown(first)) {
+    *out = MakeDim(first);
+  } else if (first_value == kUnknownDim || second_value == kUnknownDim) {
     *out = UnknownDim();
   } else {
-    const int64 v = Value(first);
-    const int64 sum = v + second_value;
-    if (second_value > 0 && sum < 0) {
-      return errors::InvalidArgument("Dimension size overflow from adding ", v,
-                                     " and ", second_value);
-    } else if (second_value < 0 && sum < 0) {
-      return errors::InvalidArgument("Negative dimension size from adding ", v,
-                                     " and ", second_value);
+    // Invariant: Both values are known and positive.
+    const int64 sum = first_value + second_value;
+    if (sum < 0) {
+      return errors::InvalidArgument("Dimension size overflow from adding ",
+                                     first_value, " and ", second_value);
     }
     *out = MakeDim(sum);
   }
   return Status::OK();
 }
 
-Status InferenceContext::Multiply(const Dimension* first,
+Status InferenceContext::Subtract(const Dimension* first,
                                   DimensionOrConstant second,
                                   const Dimension** out) {
-  int64 first_value = -1;
-  // Special cases for multiply are when the values are 0 or 1.
-  if (ValueKnown(first)) {
-    first_value = Value(first);
-    if (first_value == 0) {
-      *out = MakeDim(0);
-      return Status::OK();
-    }
-
-    // Output is whatever the second value is.
-    if (first_value == 1) {
-      *out = GetDimension(second);
-      return Status::OK();
+  const int64 first_value = Value(first);
+  const int64 second_value = Value(second);
+  // Special cases.
+  if (second_value == 0) {
+    *out = MakeDim(first);
+  } else if (first_value == kUnknownDim || second_value == kUnknownDim) {
+    *out = UnknownDim();
+  } else {
+    // Invariant: Both values are known, first_value is non-negative, and
+    // second_value is positive.
+    if (first_value < second_value) {
+      return errors::InvalidArgument(
+          "Negative dimension size caused by subtracting ", second_value,
+          " from ", first_value);
     }
+    *out = MakeDim(first_value - second_value);
   }
+  return Status::OK();
+}
 
-  // Same check for when the second argument is a known value.
-  // First find out if the value is known from DimOrConstant.
-  int64 second_value;
-  if (second.dim == nullptr) {
-    second_value = second.val;
+Status InferenceContext::Multiply(const Dimension* first,
+                                  DimensionOrConstant second,
+                                  const Dimension** out) {
+  const int64 first_value = Value(first);
+  const int64 second_value = Value(second);
+  // Special cases.
+  if (first_value == 0) {
+    *out = first;
+  } else if (second_value == 0) {
+    *out = MakeDim(second);
+  } else if (first_value == 1) {
+    *out = MakeDim(second);
+  } else if (second_value == 1) {
+    *out = first;
+  } else if (first_value == kUnknownDim || second_value == kUnknownDim) {
+    *out = UnknownDim();
   } else {
-    if (!ValueKnown(second.dim)) {
-      // Second value is not known and first is not a special caase
-      *out = UnknownDim();
-      return Status::OK();
+    // Invariant: Both values are known and and greater than 1.
+    const int64 product = first_value * second_value;
+    if (product < 0) {
+      return errors::InvalidArgument(
+          "Negative dimension size caused by overflow when multiplying ",
+          first_value, " and ", second_value);
     }
-    second_value = Value(second.dim);
-  }
-
-  // Now that we know whether the value is known, apply the special
-  // casing.
-  if (second_value == 0) {
-    *out = MakeDim(0);
-    return Status::OK();
+    *out = MakeDim(product);
   }
+  return Status::OK();
+}
 
-  // Output is whatever the first value is.
-  if (second_value == 1) {
+Status InferenceContext::Min(const Dimension* first, DimensionOrConstant second,
+                             const Dimension** out) {
+  const int64 first_value = Value(first);
+  const int64 second_value = Value(second);
+  if (first_value == 0) {
     *out = first;
-    return Status::OK();
-  }
-
-  if (!ValueKnown(first)) {
-    // First value is not known and second is not a special caase
+  } else if (second_value == 0) {
+    *out = MakeDim(second);
+  } else if (first_value == kUnknownDim || second_value == kUnknownDim) {
     *out = UnknownDim();
-    return Status::OK();
+  } else {
+    if (first_value <= second_value) {
+      *out = first;
+    } else {
+      *out = MakeDim(second);
+    }
   }
+  return Status::OK();
+}
 
-  const int64 product = first_value * second_value;
-  if (product < 0) {
-    return errors::InvalidArgument("Negative dimension size from multiplying ",
-                                   first_value, " and ", second_value);
+Status InferenceContext::Max(const Dimension* first, DimensionOrConstant second,
+                             const Dimension** out) {
+  const int64 first_value = Value(first);
+  const int64 second_value = Value(second);
+  if (first_value == kUnknownDim || second_value == kUnknownDim) {
+    *out = UnknownDim();
+  } else {
+    if (first_value >= second_value) {
+      *out = first;
+    } else {
+      *out = MakeDim(second);
+    }
   }
-  *out = MakeDim(product);
   return Status::OK();
 }
 
diff --git a/tensorflow/core/framework/shape_inference.h b/tensorflow/core/framework/shape_inference.h
index 1aa51f5017..f35c8a4c81 100644
--- a/tensorflow/core/framework/shape_inference.h
+++ b/tensorflow/core/framework/shape_inference.h
@@ -46,7 +46,7 @@ class Dimension {
 class Shape {
  private:
   Shape();
-  Shape(std::vector<const Dimension*> dims);
+  Shape(const std::vector<const Dimension*>& dims);
   ~Shape() {}
 
   const int32 rank_;
@@ -61,13 +61,17 @@ class Shape {
 struct DimensionOrConstant {
  public:
   // Intentionally not explicit.
-  DimensionOrConstant(const Dimension* dim) : dim(dim) {}
+  DimensionOrConstant(const Dimension* dim);
 
   // val must be non-negative or InferenceContext::kUnknownDim.
-  DimensionOrConstant(int64 val) : val(val) {}
+  DimensionOrConstant(int64 val);
 
-  const Dimension* dim = nullptr;
-  int64 val = 0;
+  // dim takes precedence. If dim != nullptr, val is ignored.
+  const Dimension* dim;
+  int64 val;
+
+ private:
+  DimensionOrConstant();
 };
 
 // Note: This is experimental support for op shape inference in C++.  Shape
@@ -81,8 +85,8 @@ struct DimensionOrConstant {
 // by the InferenceContext.
 class InferenceContext {
  public:
-  static constexpr int32 kUnknownRank = -1;
   static constexpr int64 kUnknownDim = -1;
+  static constexpr int32 kUnknownRank = -1;
 
   // This is a temporary constructor used for initial testing.
   //
@@ -127,8 +131,12 @@ class InferenceContext {
   }
   int32 Rank(const Shape* s) { return s->rank_; }
   bool RankKnown(const Shape* s) { return Rank(s) != kUnknownRank; }
-  int64 Value(const Dimension* d) { return d->value_; }
-  bool ValueKnown(const Dimension* d) { return Value(d) != kUnknownDim; }
+  inline int64 Value(DimensionOrConstant d) {
+    return d.dim ? d.dim->value_ : d.val;
+  }
+  inline bool ValueKnown(DimensionOrConstant d) {
+    return Value(d) != kUnknownDim;
+  }
 
   // Returns true if the rank and all dimensions of the Shape are known.
   bool FullyDefined(const Shape* s);
@@ -232,8 +240,15 @@ class InferenceContext {
 
   // Returns a new dimension of the given size.  The returned value is owned by
   // this context.
-  const Dimension* MakeDim(int64 value);
-  const Dimension* UnknownDim();
+  inline const Dimension* MakeDim(DimensionOrConstant d) {
+    if (d.dim) {
+      return d.dim;
+    } else {
+      all_dims_.push_back(new Dimension(d.val));
+      return all_dims_.back();
+    }
+  }
+  inline const Dimension* UnknownDim() { return MakeDim(kUnknownDim); }
 
   // Returns a new dimension whose value is given by a scalar input tensor.
   // The input tensor must be in host memory, since it is dereferenced to get
@@ -247,7 +262,8 @@ class InferenceContext {
   Status GetAttr(StringPiece attr_name, T* value) const;
 
   // Returns in <out> the result of dividing <dividend> by <divisor>.
-  // Returns an error if <divisor> does not evenly divide <dividend>.
+  // Returns an error if <divisor>  is not positive or does not evenly
+  // divide <dividend>.
   Status Divide(const Dimension* dividend, int64 divisor,
                 const Dimension** out);
 
@@ -255,10 +271,25 @@ class InferenceContext {
   Status Add(const Dimension* first, DimensionOrConstant second,
              const Dimension** out);
 
+  // Returns in <out> the dimension that is <first> minus <second>.
+  Status Subtract(const Dimension* first, DimensionOrConstant second,
+                  const Dimension** out);
+
   // Returns in <out> the product of <first> and <second>.
   Status Multiply(const Dimension* first, DimensionOrConstant second,
                   const Dimension** out);
 
+  // Returns in <out> the minimum of <first> and <second>. If either <first> or
+  // <second> is zero the results is zero. Otherwise, if either <first> or
+  // <second> is unknown the results is unknown.
+  Status Min(const Dimension* first, DimensionOrConstant second,
+             const Dimension** out);
+
+  // Returns in <out> the maximum of <first> and <second>. If either <first> or
+  // <second> is unknown the results is unknown.
+  Status Max(const Dimension* first, DimensionOrConstant second,
+             const Dimension** out);
+
   Status construction_status() const { return construction_status_; }
 
   // Validates that 'dim' has a known value, and prints an error
@@ -307,12 +338,30 @@ class InferenceContext {
 // Template and inline method implementations, please ignore
 
 inline Dimension::Dimension() : value_(InferenceContext::kUnknownDim) {}
-inline Dimension::Dimension(int64 value) : value_(value) {}
+inline Dimension::Dimension(int64 value) : value_(value) {
+  DCHECK(value >= 0 || value == InferenceContext::kUnknownDim)
+      << "Dimension must be non-negative or equal to "
+         "InferenceContext::kUnknownDim but got"
+      << value;
+}
 
 inline Shape::Shape() : rank_(InferenceContext::kUnknownRank) {}
-inline Shape::Shape(const std::vector<const Dimension*> dims)
+inline Shape::Shape(const std::vector<const Dimension*>& dims)
     : rank_(dims.size()), dims_(dims) {}
 
+inline DimensionOrConstant::DimensionOrConstant(const Dimension* dim)
+    : dim(dim) {
+  DCHECK(dim != nullptr) << "Internal error: Got nullptr for Dimension.";
+}
+
+inline DimensionOrConstant::DimensionOrConstant(int64 val)
+    : dim(nullptr), val(val) {
+  DCHECK(val >= 0 || val == InferenceContext::kUnknownDim)
+      << "Dimension must be non-negative or equal to "
+         "InferenceContext::kUnknownDim but got"
+      << val;
+}
+
 template <class T>
 Status InferenceContext::GetAttr(StringPiece attr_name, T* value) const {
   return GetNodeAttr(node_def_, attr_name, value);
diff --git a/tensorflow/core/framework/shape_inference_test.cc b/tensorflow/core/framework/shape_inference_test.cc
index fffb25da6d..1ecba2839a 100644
--- a/tensorflow/core/framework/shape_inference_test.cc
+++ b/tensorflow/core/framework/shape_inference_test.cc
@@ -36,6 +36,19 @@ static OpDef MakeOpDef(int num_inputs, int num_outputs) {
   return op_reg_data.op_def;
 }
 
+TEST(ShapeInferenceTest, DimensionOrConstant) {
+  NodeDef def;
+  InferenceContext c(&def, MakeOpDef(1, 1), {"?"}, {});
+  EXPECT_EQ(InferenceContext::kUnknownDim,
+            c.Value(InferenceContext::kUnknownDim));
+  EXPECT_EQ(1, c.Value(1));
+
+#ifndef NDEBUG
+  // Only run death test if DCHECKS are enabled.
+  EXPECT_DEATH(c.Value(-7), "Dimension must be non\\-negative or equal to");
+#endif
+}
+
 TEST(ShapeInferenceTest, RankAndDimInspection) {
   NodeDef def;
   InferenceContext c(&def, MakeOpDef(3, 2), {"?", "[1,?,3]", "[]"}, {});
@@ -767,15 +780,20 @@ TEST(ShapeInferenceTest, Divide) {
 
   EXPECT_EQ("Dimension size must be divisible by 5 but is 6",
             c.Divide(d_6, 5, &out).error_message());
+  EXPECT_EQ("Divisor must be positive but is 0",
+            c.Divide(d_6, 0, &out).error_message());
+  EXPECT_EQ("Divisor must be positive but is -1",
+            c.Divide(d_6, -1, &out).error_message());
 }
 
 TEST(ShapeInferenceTest, Add) {
   NodeDef def;
-  InferenceContext c(&def, MakeOpDef(1, 2), {"[6,?]"}, {});
+  InferenceContext c(&def, MakeOpDef(1, 2), {"[6,?,0]"}, {});
 
   auto s = c.input(0);
   auto d_6 = c.Dim(s, 0);
   auto d_unknown = c.Dim(s, 1);
+  auto d_0 = c.Dim(s, 2);
 
   // Adding non-zero to unknown gives new unknown.
   const Dimension* out;
@@ -790,16 +808,14 @@ TEST(ShapeInferenceTest, Add) {
   EXPECT_TRUE(out == d_6);
 
   // Adding dimension with value 0 to anything gives input.
-  EXPECT_TRUE(c.Add(d_unknown, c.MakeDim(0), &out).ok());
+  EXPECT_TRUE(c.Add(d_unknown, c.MakeDim(0ll), &out).ok());
   EXPECT_TRUE(out == d_unknown);
-  EXPECT_TRUE(c.Add(d_6, c.MakeDim(0), &out).ok());
+  EXPECT_TRUE(c.Add(d_6, c.MakeDim(0ll), &out).ok());
   EXPECT_TRUE(out == d_6);
 
   // Test addition.
   EXPECT_TRUE(c.Add(d_6, 2, &out).ok());
   EXPECT_EQ("8", c.DebugString(out));
-  EXPECT_TRUE(c.Add(d_6, -6, &out).ok());
-  EXPECT_EQ("0", c.DebugString(out));
   EXPECT_TRUE(c.Add(d_6, std::numeric_limits<int64>::max() - 6, &out).ok());
   EXPECT_EQ(std::numeric_limits<int64>::max(), c.Value(out));
 
@@ -811,14 +827,62 @@ TEST(ShapeInferenceTest, Add) {
   EXPECT_EQ(std::numeric_limits<int64>::max(), c.Value(out));
   EXPECT_TRUE(c.Add(d_6, c.UnknownDim(), &out).ok());
   EXPECT_EQ("?", c.DebugString(out));
+  EXPECT_TRUE(c.Add(d_0, d_6, &out).ok());
+  EXPECT_TRUE(out == d_6);
 
-  EXPECT_EQ("Negative dimension size from adding 6 and -7",
-            c.Add(d_6, -7, &out).error_message());
   EXPECT_EQ(
       "Dimension size overflow from adding 6 and 9223372036854775802",
       c.Add(d_6, std::numeric_limits<int64>::max() - 5, &out).error_message());
 }
 
+TEST(ShapeInferenceTest, Subtract) {
+  NodeDef def;
+  InferenceContext c(&def, MakeOpDef(1, 2), {"[6,?,0,5]"}, {});
+
+  auto s = c.input(0);
+  auto d_6 = c.Dim(s, 0);
+  auto d_unknown = c.Dim(s, 1);
+  auto d_0 = c.Dim(s, 2);
+  auto d_5 = c.Dim(s, 3);
+
+  // Subtracting non-zero from unknown gives new unknown.
+  const Dimension* out;
+  EXPECT_TRUE(c.Subtract(d_unknown, 1, &out).ok());
+  EXPECT_EQ("?", c.DebugString(out));
+  EXPECT_TRUE(out != d_unknown);
+
+  // Subtracting 0 from anything gives input.
+  EXPECT_TRUE(c.Subtract(d_unknown, 0ll, &out).ok());
+  EXPECT_TRUE(out == d_unknown);
+  EXPECT_TRUE(c.Subtract(d_6, 0ll, &out).ok());
+  EXPECT_TRUE(out == d_6);
+
+  // Subtracting dimension with value 0 from anything gives input.
+  EXPECT_TRUE(c.Subtract(d_unknown, c.MakeDim(0ll), &out).ok());
+  EXPECT_TRUE(out == d_unknown);
+  EXPECT_TRUE(c.Subtract(d_6, c.MakeDim(0ll), &out).ok());
+  EXPECT_TRUE(out == d_6);
+
+  // Test subtraction.
+  EXPECT_TRUE(c.Subtract(d_6, 2, &out).ok());
+  EXPECT_EQ("4", c.DebugString(out));
+  EXPECT_TRUE(c.Subtract(d_6, 6, &out).ok());
+  EXPECT_EQ("0", c.DebugString(out));
+
+  // Test subtraction using dimension as second value.
+  EXPECT_TRUE(c.Subtract(d_6, c.MakeDim(2), &out).ok());
+  EXPECT_EQ("4", c.DebugString(out));
+  EXPECT_TRUE(c.Subtract(d_6, d_5, &out).ok());
+  EXPECT_EQ("1", c.DebugString(out));
+  EXPECT_TRUE(c.Subtract(d_6, c.UnknownDim(), &out).ok());
+  EXPECT_EQ("?", c.DebugString(out));
+  EXPECT_TRUE(c.Subtract(d_6, d_0, &out).ok());
+  EXPECT_TRUE(out == d_6);
+
+  EXPECT_EQ("Negative dimension size caused by subtracting 6 from 5",
+            c.Subtract(d_5, d_6, &out).error_message());
+}
+
 TEST(ShapeInferenceTest, Multiply) {
   NodeDef def;
   InferenceContext c(&def, MakeOpDef(1, 2), {"[6,?,0,1]"}, {});
@@ -831,7 +895,7 @@ TEST(ShapeInferenceTest, Multiply) {
 
   // Multiplying non-zero to unknown gives new unknown.
   const Dimension* out;
-  EXPECT_TRUE(c.Multiply(d_unknown, 1, &out).ok());
+  EXPECT_TRUE(c.Multiply(d_unknown, 2, &out).ok());
   EXPECT_EQ("?", c.DebugString(out));
 
   // Multiplying 0 to anything gives 0.
@@ -844,19 +908,19 @@ TEST(ShapeInferenceTest, Multiply) {
 
   // Multiplying 1 to anything gives the original.
   // (unknown -> unknown)
-  EXPECT_TRUE(c.Multiply(d_unknown, static_cast<int64>(1), &out).ok());
-  EXPECT_EQ("?", c.DebugString(out));
+  EXPECT_TRUE(c.Multiply(d_unknown, 1, &out).ok());
+  EXPECT_EQ(d_unknown, out);
   EXPECT_TRUE(c.Multiply(d_unknown, d_1, &out).ok());
-  EXPECT_EQ("?", c.DebugString(out));
+  EXPECT_EQ(d_unknown, out);
   EXPECT_TRUE(c.Multiply(d_1, d_unknown, &out).ok());
-  EXPECT_EQ("?", c.DebugString(out));
+  EXPECT_EQ(d_unknown, out);
   // (known -> known)
-  EXPECT_TRUE(c.Multiply(d_6, static_cast<int64>(1), &out).ok());
-  EXPECT_EQ("6", c.DebugString(out));
+  EXPECT_TRUE(c.Multiply(d_6, 1, &out).ok());
+  EXPECT_EQ(d_6, out);
   EXPECT_TRUE(c.Multiply(d_6, d_1, &out).ok());
-  EXPECT_EQ("6", c.DebugString(out));
+  EXPECT_EQ(d_6, out);
   EXPECT_TRUE(c.Multiply(d_1, d_6, &out).ok());
-  EXPECT_EQ("6", c.DebugString(out));
+  EXPECT_EQ(d_6, out);
 
   // Test multiplication.
   EXPECT_TRUE(c.Multiply(d_6, 2, &out).ok());
@@ -869,9 +933,6 @@ TEST(ShapeInferenceTest, Multiply) {
   EXPECT_EQ("12", c.DebugString(out));
   EXPECT_TRUE(c.Multiply(d_6, c.UnknownDim(), &out).ok());
   EXPECT_EQ("?", c.DebugString(out));
-
-  EXPECT_EQ("Negative dimension size from multiplying 6 and -7",
-            c.Multiply(d_6, -7, &out).error_message());
 }
 
 TEST(ShapeInferenceTest, FullyDefined) {
@@ -895,5 +956,90 @@ TEST(ShapeInferenceTest, ValidateKnownDim) {
   EXPECT_TRUE(c.ValidateKnownDim(c.Dim(c.Matrix(1, 2), 0), "known").ok());
 }
 
+TEST(ShapeInferenceTest, Min) {
+  NodeDef def;
+  InferenceContext c(&def, MakeOpDef(1, 2), {"[1,2,?,0]"}, {});
+
+  auto s = c.input(0);
+  auto d_1 = c.Dim(s, 0);
+  auto d_2 = c.Dim(s, 1);
+  auto d_unknown = c.Dim(s, 2);
+  auto d_0 = c.Dim(s, 3);
+
+  // Minimum involving zero and unknown returns zero.
+  const Dimension* out;
+  EXPECT_TRUE(c.Min(d_0, d_unknown, &out).ok());
+  EXPECT_EQ(d_0, out);
+  EXPECT_TRUE(c.Min(d_unknown, d_0, &out).ok());
+  EXPECT_EQ(d_0, out);
+  EXPECT_TRUE(c.Min(c.MakeDim(0ll), d_unknown, &out).ok());
+  EXPECT_EQ("0", c.DebugString(out));
+  EXPECT_TRUE(c.Min(d_unknown, 0ll, &out).ok());
+  EXPECT_EQ("0", c.DebugString(out));
+
+  // Minimum involving unknowns and non-zeros gives new unknown.
+  EXPECT_TRUE(c.Min(d_unknown, d_unknown, &out).ok());
+  EXPECT_EQ("?", c.DebugString(out));
+  EXPECT_TRUE(c.Min(d_unknown, 1, &out).ok());
+  EXPECT_EQ("?", c.DebugString(out));
+  EXPECT_TRUE(c.Min(d_1, d_unknown, &out).ok());
+  EXPECT_EQ("?", c.DebugString(out));
+
+  // Minimum with constant second arg.
+  EXPECT_TRUE(c.Min(d_1, 1, &out).ok());
+  EXPECT_EQ(d_1, out);
+  EXPECT_TRUE(c.Min(d_1, 3, &out).ok());
+  EXPECT_EQ(d_1, out);
+  EXPECT_TRUE(c.Min(d_2, 1, &out).ok());
+  EXPECT_EQ("1", c.DebugString(out));
+
+  // Minimum with two dimensions.
+  EXPECT_TRUE(c.Min(d_1, d_1, &out).ok());
+  EXPECT_EQ(d_1, out);
+  EXPECT_TRUE(c.Min(d_1, d_2, &out).ok());
+  EXPECT_EQ(d_1, out);
+  EXPECT_TRUE(c.Min(d_2, d_1, &out).ok());
+  EXPECT_EQ(d_1, out);
+  EXPECT_TRUE(c.Min(d_2, d_2, &out).ok());
+  EXPECT_EQ(d_2, out);
+}
+
+TEST(ShapeInferenceTest, Max) {
+  NodeDef def;
+  InferenceContext c(&def, MakeOpDef(1, 2), {"[1,2,?]"}, {});
+
+  auto s = c.input(0);
+  auto d_1 = c.Dim(s, 0);
+  auto d_2 = c.Dim(s, 1);
+  auto d_unknown = c.Dim(s, 2);
+
+  // Maximum involving unknowns gives new unknown.
+  const Dimension* out;
+  EXPECT_TRUE(c.Max(d_unknown, d_unknown, &out).ok());
+  EXPECT_EQ("?", c.DebugString(out));
+  EXPECT_TRUE(c.Max(d_unknown, 1, &out).ok());
+  EXPECT_EQ("?", c.DebugString(out));
+  EXPECT_TRUE(c.Max(d_1, d_unknown, &out).ok());
+  EXPECT_EQ("?", c.DebugString(out));
+
+  // Maximum with constant second arg.
+  EXPECT_TRUE(c.Max(d_1, 1, &out).ok());
+  EXPECT_EQ(d_1, out);
+  EXPECT_TRUE(c.Max(d_2, 1, &out).ok());
+  EXPECT_EQ(d_2, out);
+  EXPECT_TRUE(c.Max(d_2, 3, &out).ok());
+  EXPECT_EQ("3", c.DebugString(out));
+
+  // Maximum with two dimensions.
+  EXPECT_TRUE(c.Max(d_1, d_1, &out).ok());
+  EXPECT_EQ(d_1, out);
+  EXPECT_TRUE(c.Max(d_1, d_2, &out).ok());
+  EXPECT_EQ(d_2, out);
+  EXPECT_TRUE(c.Max(d_2, d_1, &out).ok());
+  EXPECT_EQ(d_2, out);
+  EXPECT_TRUE(c.Max(d_2, d_2, &out).ok());
+  EXPECT_EQ(d_2, out);
+}
+
 }  // namespace shape_inference
 }  // namespace tensorflow
diff --git a/tensorflow/core/framework/shape_inference_testutil.cc b/tensorflow/core/framework/shape_inference_testutil.cc
index c1e55d032d..60a9cb101f 100644
--- a/tensorflow/core/framework/shape_inference_testutil.cc
+++ b/tensorflow/core/framework/shape_inference_testutil.cc
@@ -40,6 +40,11 @@ Status InferShapes(ShapeInferenceTestOp op, const string& ins,
   shape_inference::InferenceContext c(&op.node_def, op_reg_data->op_def, ins_v,
                                       op.input_tensors);
   TF_RETURN_IF_ERROR(c.construction_status());
+  if (op_reg_data->shape_inference_fn == nullptr) {
+    return errors::InvalidArgument(
+        "No shape inference function exists for op '", op.name,
+        "', did you forget to define it?");
+  }
   TF_RETURN_IF_ERROR(op_reg_data->shape_inference_fn(&c));
   const int num_outputs = c.num_outputs();