writer/hlsl: Zero initialize with (T) 0

For structures and arrays.
This behaves identically to the per-element zero-initialization, but can be significantly less verbose.

Change-Id: I380ef86f16c2b3f37a9de2820e707f368955b761
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/56764
Auto-Submit: Ben Clayton <bclayton@google.com>
Reviewed-by: David Neto <dneto@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>

src/writer/hlsl/generator_impl.cc

@@ -2508,38 +2508,13 @@ bool GeneratorImpl::EmitZeroValue(std::ostream& out, const sem::Type* type) {
         return false;
       }
     }
-  } else if (auto* str = type->As<sem::Struct>()) {
-    auto it = structure_builders_.find(str);
-    if (it != structure_builders_.end()) {
-      out << it->second << "(";
-    } else {
-      out << "{";
+  } else if (type->IsAnyOf<sem::Struct, sem::Array>()) {
+    out << "(";
+    if (!EmitType(out, type, ast::StorageClass::kNone, ast::Access::kUndefined,
+                  "")) {
+      return false;
     }
-
-    bool first = true;
-    for (auto* member : str->Members()) {
-      if (!first) {
-        out << ", ";
-      }
-      first = false;
-      if (!EmitZeroValue(out, member->Type())) {
-        return false;
-      }
-    }
-
-    out << (it != structure_builders_.end() ? ")" : "}");
-  } else if (auto* arr = type->As<sem::Array>()) {
-    out << "{";
-    auto* elem = arr->ElemType();
-    for (size_t i = 0; i < arr->Count(); i++) {
-      if (i > 0) {
-        out << ", ";
-      }
-      if (!EmitZeroValue(out, elem)) {
-        return false;
-      }
-    }
-    out << "}";
+    out << ")0";
   } else {
     diagnostics_.add_error(
         diag::System::Writer,

src/writer/hlsl/generator_impl_constructor_test.cc

@@ -233,7 +233,7 @@ TEST_F(HlslGeneratorImplTest_Constructor, EmitConstructor_Type_Struct_Empty) {
   GeneratorImpl& gen = SanitizeAndBuild();
 
   ASSERT_TRUE(gen.Generate()) << gen.error();
-  EXPECT_THAT(gen.result(), HasSubstr("{0, 0.0f, int3(0, 0, 0)}"));
+  EXPECT_THAT(gen.result(), HasSubstr("(S)0"));
 }
 
 }  // namespace

src/writer/hlsl/generator_impl_function_test.cc

@@ -784,7 +784,7 @@ struct tint_array_wrapper {
 };
 
 tint_array_wrapper my_func() {
-  const tint_array_wrapper tint_symbol = {{0.0f, 0.0f, 0.0f, 0.0f, 0.0f}};
+  const tint_array_wrapper tint_symbol = {(float[5])0};
   return tint_symbol;
 }
 )"));

src/writer/hlsl/generator_impl_member_accessor_test.cc

@@ -136,7 +136,7 @@ TEST_F(HlslGeneratorImplTest_MemberAccessor, EmitExpression_MemberAccessor) {
   float mem;
 };
 
-static Data str = {0.0f};
+static Data str = (Data)0;
 
 [numthreads(1, 1, 1)]
 void test_function() {

src/writer/hlsl/generator_impl_variable_decl_statement_test.cc

@@ -61,8 +61,7 @@ TEST_F(HlslGeneratorImplTest_VariableDecl, Emit_VariableDeclStatement_Array) {
   gen.increment_indent();
 
   ASSERT_TRUE(gen.Generate()) << gen.error();
-  EXPECT_THAT(gen.result(),
-              HasSubstr("  float a[5] = {0.0f, 0.0f, 0.0f, 0.0f, 0.0f};\n"));
+  EXPECT_THAT(gen.result(), HasSubstr("  float a[5] = (float[5])0;\n"));
 }
 
 TEST_F(HlslGeneratorImplTest_VariableDecl, Emit_VariableDeclStatement_Private) {

src/writer/text_generator.h

@@ -81,7 +81,7 @@ class TextGenerator {
     ~LineWriter();
 
     /// @returns the ostringstream
-    operator std::ostream &() { return os; }
+    operator std::ostream&() { return os; }
 
     /// @param rhs the value to write to the line
     /// @returns the ostream so calls can be chained