tint/sem: Add more helpers to Constant

Many backends can produce cleaner code if all the elements are zero or
the same value.

Bug: tint:1504
Change-Id: Iff3227884473b0be42395e4a637a7fe0b7a1b238
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/91966
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>

src/tint/sem/constant.cc

@@ -45,9 +45,9 @@ Constant& Constant::operator=(const Constant& rhs) = default;
 
 bool Constant::AnyZero() const {
     return WithElements([&](auto&& vec) {
-        for (auto scalar : vec) {
+        using T = typename std::decay_t<decltype(vec)>::value_type;
-            using T = std::remove_reference_t<decltype(scalar)>;
+        for (auto el : vec) {
-            if (scalar == T(0)) {
+            if (el == T(0)) {
                 return true;
             }
         }
@@ -55,6 +55,32 @@ bool Constant::AnyZero() const {
     });
 }
 
+bool Constant::AllZero() const {
+    return WithElements([&](auto&& vec) {
+        using T = typename std::decay_t<decltype(vec)>::value_type;
+        for (auto el : vec) {
+            if (el != T(0)) {
+                return false;
+            }
+        }
+        return true;
+    });
+}
+
+bool Constant::AllEqual(size_t start, size_t end) const {
+    return WithElements([&](auto&& vec) {
+        if (!vec.empty()) {
+            auto value = vec[start];
+            for (size_t i = start + 1; i < end; i++) {
+                if (vec[i] != value) {
+                    return false;
+                }
+            }
+        }
+        return true;
+    });
+}
+
 const Type* Constant::CheckElemType(const sem::Type* ty, size_t num_elements) {
     diag::List diag;
     if (ty->is_abstract_or_scalar() || ty->IsAnyOf<Vector, Matrix>()) {

src/tint/sem/constant.h

@@ -132,6 +132,17 @@ class Constant {
     /// @returns true if any element is zero
     bool AnyZero() const;
 
+    /// @returns true if all elements are zero
+    bool AllZero() const;
+
+    /// @returns true if all elements are the same value
+    bool AllEqual() const { return AllEqual(0, ElementCount()); }
+
+    /// @param start the first element index
+    /// @param end one past the last element index
+    /// @returns true if all elements between `[start, end)` are the same value
+    bool AllEqual(size_t start, size_t end) const;
+
     /// @param index the index of the element
     /// @return the element at `index`, which must be of type `T`.
     template <typename T>

src/tint/sem/constant_test.cc

@@ -195,5 +195,43 @@ TEST_F(ConstantTest, Element_mat2x3_f16) {
     EXPECT_EQ(c.ElementCount(), 6u);
 }
 
+TEST_F(ConstantTest, AnyZero) {
+    auto* vec3_ai = create<Vector>(create<AbstractInt>(), 3u);
+    EXPECT_EQ(Constant(vec3_ai, {1_a, 2_a, 3_a}).AnyZero(), false);
+    EXPECT_EQ(Constant(vec3_ai, {0_a, 2_a, 3_a}).AnyZero(), true);
+    EXPECT_EQ(Constant(vec3_ai, {1_a, 0_a, 3_a}).AnyZero(), true);
+    EXPECT_EQ(Constant(vec3_ai, {1_a, 2_a, 0_a}).AnyZero(), true);
+    EXPECT_EQ(Constant(vec3_ai, {0_a, 0_a, 0_a}).AnyZero(), true);
+}
+
+TEST_F(ConstantTest, AllZero) {
+    auto* vec3_ai = create<Vector>(create<AbstractInt>(), 3u);
+    EXPECT_EQ(Constant(vec3_ai, {1_a, 2_a, 3_a}).AllZero(), false);
+    EXPECT_EQ(Constant(vec3_ai, {0_a, 2_a, 3_a}).AllZero(), false);
+    EXPECT_EQ(Constant(vec3_ai, {1_a, 0_a, 3_a}).AllZero(), false);
+    EXPECT_EQ(Constant(vec3_ai, {1_a, 2_a, 0_a}).AllZero(), false);
+    EXPECT_EQ(Constant(vec3_ai, {0_a, 0_a, 0_a}).AllZero(), true);
+}
+
+TEST_F(ConstantTest, AllEqual) {
+    auto* vec3_ai = create<Vector>(create<AbstractInt>(), 3u);
+    EXPECT_EQ(Constant(vec3_ai, {1_a, 2_a, 3_a}).AllEqual(), false);
+    EXPECT_EQ(Constant(vec3_ai, {1_a, 1_a, 3_a}).AllEqual(), false);
+    EXPECT_EQ(Constant(vec3_ai, {1_a, 3_a, 3_a}).AllEqual(), false);
+    EXPECT_EQ(Constant(vec3_ai, {1_a, 1_a, 1_a}).AllEqual(), true);
+    EXPECT_EQ(Constant(vec3_ai, {2_a, 2_a, 2_a}).AllEqual(), true);
+    EXPECT_EQ(Constant(vec3_ai, {3_a, 3_a, 3_a}).AllEqual(), true);
+}
+
+TEST_F(ConstantTest, AllEqualRange) {
+    auto* vec3_ai = create<Vector>(create<AbstractInt>(), 3u);
+    EXPECT_EQ(Constant(vec3_ai, {1_a, 2_a, 3_a}).AllEqual(1, 3), false);
+    EXPECT_EQ(Constant(vec3_ai, {1_a, 1_a, 3_a}).AllEqual(1, 3), false);
+    EXPECT_EQ(Constant(vec3_ai, {1_a, 3_a, 3_a}).AllEqual(1, 3), true);
+    EXPECT_EQ(Constant(vec3_ai, {1_a, 1_a, 1_a}).AllEqual(1, 3), true);
+    EXPECT_EQ(Constant(vec3_ai, {2_a, 2_a, 2_a}).AllEqual(1, 3), true);
+    EXPECT_EQ(Constant(vec3_ai, {2_a, 2_a, 3_a}).AllEqual(1, 3), false);
+}
+
 }  // namespace
 }  // namespace tint::sem