writer/hlsl: Zero-initialize var declarations

Don't construct these with undefined values

Change-Id: I6225d9be0973ebc1a8594526aa32ec6775b5e865
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/51300
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: David Neto <dneto@google.com>

src/writer/hlsl/generator_impl.cc

@@ -2092,7 +2092,7 @@ bool GeneratorImpl::EmitLiteral(std::ostream& out, ast::Literal* lit) {
   return true;
 }
 
-bool GeneratorImpl::EmitZeroValue(std::ostream& out, sem::Type* type) {
+bool GeneratorImpl::EmitZeroValue(std::ostream& out, const sem::Type* type) {
   if (type->Is<sem::Bool>()) {
     out << "false";
   } else if (type->Is<sem::F32>()) {
@@ -2142,6 +2142,18 @@ bool GeneratorImpl::EmitZeroValue(std::ostream& out, sem::Type* type) {
       }
     }
     out << "}";
+  } 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 << "}";
   } else {
     diagnostics_.add_error("Invalid type for zero emission: " +
                            type->type_name());
@@ -2626,6 +2638,9 @@ bool GeneratorImpl::EmitVariable(std::ostream& out,
                                  bool skip_constructor) {
   make_indent(out);
 
+  auto* sem = builder_.Sem().Get(var);
+  auto* type = sem->Type();
+
   // TODO(dsinclair): Handle variable decorations
   if (!var->decorations().empty()) {
     diagnostics_.add_error("Variable decorations are not handled yet");
@@ -2633,21 +2648,25 @@ bool GeneratorImpl::EmitVariable(std::ostream& out,
   }
 
   std::ostringstream constructor_out;
-  if (!skip_constructor && var->constructor() != nullptr) {
+  if (!skip_constructor) {
     constructor_out << " = ";
 
+    if (var->constructor()) {
       std::ostringstream pre;
       if (!EmitExpression(pre, constructor_out, var->constructor())) {
         return false;
       }
       out << pre.str();
+    } else {
+      if (!EmitZeroValue(constructor_out, type)) {
+        return false;
+      }
+    }
   }
 
   if (var->is_const()) {
     out << "const ";
   }
-  auto* sem = builder_.Sem().Get(var);
-  auto* type = sem->Type();
   if (!EmitType(out, type, sem->StorageClass(), sem->AccessControl(),
                 builder_.Symbols().NameFor(var->symbol()))) {
     return false;

src/writer/hlsl/generator_impl.h

@@ -315,7 +315,7 @@ class GeneratorImpl : public TextGenerator {
   /// @param out the output stream
   /// @param type the type to emit the value for
   /// @returns true if the zero value was successfully emitted.
-  bool EmitZeroValue(std::ostream& out, sem::Type* type);
+  bool EmitZeroValue(std::ostream& out, const sem::Type* type);
   /// Handles generating a variable
   /// @param out the output stream
   /// @param var the variable to generate

src/writer/hlsl/generator_impl_variable_decl_statement_test.cc

@@ -35,7 +35,7 @@ TEST_F(HlslGeneratorImplTest_VariableDecl, Emit_VariableDeclStatement) {
   gen.increment_indent();
 
   ASSERT_TRUE(gen.EmitStatement(out, stmt)) << gen.error();
-  EXPECT_EQ(result(), "  float a;\n");
+  EXPECT_EQ(result(), "  float a = 0.0f;\n");
 }
 
 TEST_F(HlslGeneratorImplTest_VariableDecl, Emit_VariableDeclStatement_Const) {
@@ -61,7 +61,8 @@ TEST_F(HlslGeneratorImplTest_VariableDecl, Emit_VariableDeclStatement_Array) {
   gen.increment_indent();
 
   ASSERT_TRUE(gen.Generate(out)) << gen.error();
-  EXPECT_THAT(result(), HasSubstr("  float a[5];\n"));
+  EXPECT_THAT(result(),
+              HasSubstr("  float a[5] = {0.0f, 0.0f, 0.0f, 0.0f, 0.0f};\n"));
 }
 
 TEST_F(HlslGeneratorImplTest_VariableDecl, Emit_VariableDeclStatement_Private) {

test/access/var/matrix.wgsl.expected.hlsl

@@ -1,6 +1,6 @@
 [numthreads(1, 1, 1)]
 void main() {
-  float3x3 m;
+  float3x3 m = float3x3(0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f);
   const float3 v = m[1];
   const float f = v[1];
   return;

test/access/var/vector.wgsl.expected.hlsl

@@ -1,6 +1,6 @@
 [numthreads(1, 1, 1)]
 void main() {
-  float3 v;
+  float3 v = float3(0.0f, 0.0f, 0.0f);
   const float scalar = v.y;
   const float2 swizzle2 = v.xz;
   const float3 swizzle3 = v.xzy;