tint: Implement DP4a on HLSL writer

Bug: tint:1497
Test: tint_unittests
Change-Id: I29cc3e56949071230cdbd5afdc59eef076777149
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/89706
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: Jiawei Shao <jiawei.shao@intel.com>
Kokoro: Kokoro <noreply+kokoro@google.com>

src/tint/sem/builtin.cc

@@ -83,6 +83,10 @@ bool IsAtomicBuiltin(BuiltinType i) {
            i == sem::BuiltinType::kAtomicCompareExchangeWeak;
 }
 
+bool IsDP4aBuiltin(BuiltinType i) {
+    return i == sem::BuiltinType::kDot4I8Packed || i == sem::BuiltinType::kDot4U8Packed;
+}
+
 Builtin::Builtin(BuiltinType type,
                  const sem::Type* return_type,
                  std::vector<Parameter*> parameters,
@@ -135,6 +139,10 @@ bool Builtin::IsAtomic() const {
     return IsAtomicBuiltin(type_);
 }
 
+bool Builtin::IsDP4a() const {
+    return IsDP4aBuiltin(type_);
+}
+
 bool Builtin::HasSideEffects() const {
     if (IsAtomic() && type_ != sem::BuiltinType::kAtomicLoad) {
         return true;
@@ -146,13 +154,10 @@ bool Builtin::HasSideEffects() const {
 }
 
 ast::Enable::ExtensionKind Builtin::RequiredExtension() const {
-    switch (type_) {
-        case sem::BuiltinType::kDot4I8Packed:
-        case sem::BuiltinType::kDot4U8Packed:
-            return ast::Enable::ExtensionKind::kChromiumExperimentalDP4a;
-        default:
-            return ast::Enable::ExtensionKind::kNotAnExtension;
+    if (IsDP4a()) {
+        return ast::Enable::ExtensionKind::kChromiumExperimentalDP4a;
     }
+    return ast::Enable::ExtensionKind::kNotAnExtension;
 }
 
 }  // namespace tint::sem

src/tint/sem/builtin.h

@@ -70,6 +70,11 @@ bool IsBarrierBuiltin(BuiltinType i);
 /// @returns true if the given `i` is a atomic builtin
 bool IsAtomicBuiltin(BuiltinType i);
 
+/// Determins if the given `i` is a DP4a builtin
+/// @param i the builtin
+/// @returns true if the given `i` is a DP4a builtin
+bool IsDP4aBuiltin(BuiltinType i);
+
 /// Builtin holds the semantic information for a builtin function.
 class Builtin final : public Castable<Builtin, CallTarget> {
   public:
@@ -130,6 +135,10 @@ class Builtin final : public Castable<Builtin, CallTarget> {
     /// @returns true if builtin is a atomic builtin
     bool IsAtomic() const;
 
+    /// @returns true if builtin is a DP4a builtin (defined in the extension
+    /// chromium_experimental_DP4a)
+    bool IsDP4a() const;
+
     /// @returns true if intrinsic may have side-effects (i.e. writes to at least
     /// one of its inputs)
     bool HasSideEffects() const;