msl: Overload matrix-vector arithmetic operators

These operators are not defined in the metal namespace when the vector
operands are packed.

Fixed: tint:1121
Change-Id: I2e8f4302e08117ca41bac6c05fb24a70d1215740
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/62480
Kokoro: Kokoro <noreply+kokoro@google.com>
Auto-Submit: James Price <jrprice@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>

src/writer/msl/generator_impl.cc

@@ -2310,6 +2310,26 @@ bool GeneratorImpl::EmitPackedType(std::ostream& out,
     if (!EmitType(out, vec, "")) {
       return false;
     }
+
+    if (vec->is_float_vector() && !matrix_packed_vector_overloads_) {
+      // Overload operators for matrix-vector arithmetic where the vector
+      // operand is packed, as these overloads to not exist in the metal
+      // namespace.
+      TextBuffer b;
+      TINT_DEFER(helpers_.Append(b));
+      line(&b) << R"(template<typename T, int N, int M>
+inline auto operator*(matrix<T, N, M> lhs, packed_vec<T, N> rhs) {
+  return lhs * vec<T, N>(rhs);
+}
+
+template<typename T, int N, int M>
+inline auto operator*(packed_vec<T, M> lhs, matrix<T, N, M> rhs) {
+  return vec<T, M>(lhs) * rhs;
+}
+)";
+      matrix_packed_vector_overloads_ = true;
+    }
+
     return true;
   }
 

src/writer/msl/generator_impl.h

@@ -355,6 +355,9 @@ class GeneratorImpl : public TextGenerator {
   /// True if an invariant attribute has been generated.
   bool has_invariant_ = false;
 
+  /// True if matrix-packed_vector operator overloads have been generated.
+  bool matrix_packed_vector_overloads_ = false;
+
   std::unordered_map<const sem::Intrinsic*, std::string> intrinsics_;
   std::unordered_map<const sem::Type*, std::string> unary_minus_funcs_;
 };