From 2287f33424368c2a604b2ab58e316adaaad41a9a Mon Sep 17 00:00:00 2001
From: dan sinclair <dsinclair@google.com>
Date: Tue, 5 May 2020 14:21:19 +0000
Subject: [PATCH] [spirv-writer] Add null initializers where needed.

The WGSL spec requires initializers for Output, Private and Function
variables. This CL adds initializers where needed.

Bug: tint:75
Change-Id: Id97f85a67ead2ffc41d6bdd1b71bf7034b04502a
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/20980
Reviewed-by: David Neto <dneto@google.com>
---
 BUILD.gn                                      |   3 +
 src/CMakeLists.txt                            |   3 +
 src/ast/bool_literal_test.cc                  |   1 +
 src/ast/float_literal_test.cc                 |   1 +
 src/ast/int_literal_test.cc                   |   1 +
 src/ast/literal.cc                            |  10 +
 src/ast/literal.h                             |   5 +
 src/ast/null_literal.cc                       |  37 +++
 src/ast/null_literal.h                        |  46 ++++
 src/ast/null_literal_test.cc                  |  51 ++++
 src/ast/uint_literal_test.cc                  |   1 +
 src/writer/spirv/builder.cc                   |  26 +-
 .../spirv/builder_accessor_expression_test.cc | 240 ++++++++++--------
 src/writer/spirv/builder_assign_test.cc       |  48 ++--
 src/writer/spirv/builder_call_test.cc         |  19 +-
 .../spirv/builder_cast_expression_test.cc     |  11 +-
 .../builder_constructor_expression_test.cc    |  30 ++-
 src/writer/spirv/builder_entry_point_test.cc  |   9 +-
 .../spirv/builder_function_variable_test.cc   |  10 +-
 .../spirv/builder_global_variable_test.cc     |  30 ++-
 .../spirv/builder_ident_expression_test.cc    |  18 +-
 src/writer/spirv/builder_if_test.cc           | 138 +++++-----
 src/writer/spirv/builder_loop_test.cc         |  42 +--
 23 files changed, 511 insertions(+), 269 deletions(-)
 create mode 100644 src/ast/null_literal.cc
 create mode 100644 src/ast/null_literal.h
 create mode 100644 src/ast/null_literal_test.cc

diff --git a/BUILD.gn b/BUILD.gn
index 80be5fcbd8..fe75d7bdfc 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -268,6 +268,8 @@ source_set("libtint_core_src") {
     "src/ast/node.h",
     "src/ast/nop_statement.cc",
     "src/ast/nop_statement.h",
+    "src/ast/null_literal.cc",
+    "src/ast/null_literal.h",
     "src/ast/pipeline_stage.cc",
     "src/ast/pipeline_stage.h",
     "src/ast/return_statement.cc",
@@ -598,6 +600,7 @@ source_set("tint_unittests_core_src") {
     "src/ast/member_accessor_expression_test.cc",
     "src/ast/module_test.cc",
     "src/ast/nop_statement_test.cc",
+    "src/ast/null_literal_test.cc",
     "src/ast/return_statement_test.cc",
     "src/ast/scalar_constructor_expression_test.cc",
     "src/ast/set_decoration_test.cc",
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 61bc317f5e..c07fdd9458 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -105,6 +105,8 @@ set(TINT_LIB_SRCS
   ast/node.h
   ast/nop_statement.cc
   ast/nop_statement.h
+  ast/null_literal.cc
+  ast/null_literal.h
   ast/pipeline_stage.cc
   ast/pipeline_stage.h
   ast/return_statement.cc
@@ -283,6 +285,7 @@ set(TINT_TEST_SRCS
   ast/member_accessor_expression_test.cc
   ast/module_test.cc
   ast/nop_statement_test.cc
+  ast/null_literal_test.cc
   ast/binary_expression_test.cc
   ast/return_statement_test.cc
   ast/scalar_constructor_expression_test.cc
diff --git a/src/ast/bool_literal_test.cc b/src/ast/bool_literal_test.cc
index 10697ee7ce..b8dc640056 100644
--- a/src/ast/bool_literal_test.cc
+++ b/src/ast/bool_literal_test.cc
@@ -46,6 +46,7 @@ TEST_F(BoolLiteralTest, Is) {
   EXPECT_FALSE(b.IsInt());
   EXPECT_FALSE(b.IsFloat());
   EXPECT_FALSE(b.IsUint());
+  EXPECT_FALSE(b.IsNull());
 }
 
 TEST_F(BoolLiteralTest, ToStr) {
diff --git a/src/ast/float_literal_test.cc b/src/ast/float_literal_test.cc
index 6f1101806a..960a7dd42a 100644
--- a/src/ast/float_literal_test.cc
+++ b/src/ast/float_literal_test.cc
@@ -37,6 +37,7 @@ TEST_F(FloatLiteralTest, Is) {
   EXPECT_FALSE(f.IsInt());
   EXPECT_TRUE(f.IsFloat());
   EXPECT_FALSE(f.IsUint());
+  EXPECT_FALSE(f.IsNull());
 }
 
 TEST_F(FloatLiteralTest, ToStr) {
diff --git a/src/ast/int_literal_test.cc b/src/ast/int_literal_test.cc
index f3f9f81835..9bb2307e65 100644
--- a/src/ast/int_literal_test.cc
+++ b/src/ast/int_literal_test.cc
@@ -38,6 +38,7 @@ TEST_F(IntLiteralTest, Is) {
   EXPECT_TRUE(i.IsInt());
   EXPECT_FALSE(i.IsFloat());
   EXPECT_FALSE(i.IsUint());
+  EXPECT_FALSE(i.IsNull());
 }
 
 TEST_F(IntLiteralTest, ToStr) {
diff --git a/src/ast/literal.cc b/src/ast/literal.cc
index d8d64c04ed..489a32c671 100644
--- a/src/ast/literal.cc
+++ b/src/ast/literal.cc
@@ -19,6 +19,7 @@
 #include "src/ast/bool_literal.h"
 #include "src/ast/float_literal.h"
 #include "src/ast/int_literal.h"
+#include "src/ast/null_literal.h"
 #include "src/ast/uint_literal.h"
 
 namespace tint {
@@ -40,6 +41,10 @@ bool Literal::IsInt() const {
   return false;
 }
 
+bool Literal::IsNull() const {
+  return false;
+}
+
 bool Literal::IsUint() const {
   return false;
 }
@@ -59,6 +64,11 @@ IntLiteral* Literal::AsInt() {
   return static_cast<IntLiteral*>(this);
 }
 
+NullLiteral* Literal::AsNull() {
+  assert(IsNull());
+  return static_cast<NullLiteral*>(this);
+}
+
 UintLiteral* Literal::AsUint() {
   assert(IsUint());
   return static_cast<UintLiteral*>(this);
diff --git a/src/ast/literal.h b/src/ast/literal.h
index f7ae47057d..54079cd29f 100644
--- a/src/ast/literal.h
+++ b/src/ast/literal.h
@@ -25,6 +25,7 @@ namespace ast {
 class BoolLiteral;
 class FloatLiteral;
 class IntLiteral;
+class NullLiteral;
 class UintLiteral;
 
 /// Base class for a literal value
@@ -38,6 +39,8 @@ class Literal {
   virtual bool IsFloat() const;
   /// @returns true if this is a signed int literal
   virtual bool IsInt() const;
+  /// @returns true if this is a null literal
+  virtual bool IsNull() const;
   /// @returns true if this is a unsigned int literal
   virtual bool IsUint() const;
 
@@ -47,6 +50,8 @@ class Literal {
   FloatLiteral* AsFloat();
   /// @returns the literal as a int literal
   IntLiteral* AsInt();
+  /// @returns the literal as a null literal
+  NullLiteral* AsNull();
   /// @returns the literal as a unsigned int literal
   UintLiteral* AsUint();
 
diff --git a/src/ast/null_literal.cc b/src/ast/null_literal.cc
new file mode 100644
index 0000000000..7d4475199c
--- /dev/null
+++ b/src/ast/null_literal.cc
@@ -0,0 +1,37 @@
+// Copyright 2020 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "src/ast/null_literal.h"
+
+namespace tint {
+namespace ast {
+
+NullLiteral::NullLiteral(ast::type::Type* type) : Literal(type) {}
+
+NullLiteral::~NullLiteral() = default;
+
+bool NullLiteral::IsNull() const {
+  return true;
+}
+
+std::string NullLiteral::to_str() const {
+  return "null " + type()->type_name();
+}
+
+std::string NullLiteral::name() const {
+  return "__null" + type()->type_name();
+}
+
+}  // namespace ast
+}  // namespace tint
diff --git a/src/ast/null_literal.h b/src/ast/null_literal.h
new file mode 100644
index 0000000000..943117dae4
--- /dev/null
+++ b/src/ast/null_literal.h
@@ -0,0 +1,46 @@
+// Copyright 2020 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef SRC_AST_NULL_LITERAL_H_
+#define SRC_AST_NULL_LITERAL_H_
+
+#include <string>
+
+#include "src/ast/literal.h"
+
+namespace tint {
+namespace ast {
+
+/// A null literal
+class NullLiteral : public Literal {
+ public:
+  /// Constructor
+  /// @param type the type
+  NullLiteral(ast::type::Type* type);
+  ~NullLiteral() override;
+
+  /// @returns true if this is a null literal
+  bool IsNull() const override;
+
+  /// @returns the name for this literal. This name is unique to this value.
+  std::string name() const override;
+
+  /// @returns the literal as a string
+  std::string to_str() const override;
+};
+
+}  // namespace ast
+}  // namespace tint
+
+#endif  // SRC_AST_NULL_LITERAL_H_
\ No newline at end of file
diff --git a/src/ast/null_literal_test.cc b/src/ast/null_literal_test.cc
new file mode 100644
index 0000000000..67354f697d
--- /dev/null
+++ b/src/ast/null_literal_test.cc
@@ -0,0 +1,51 @@
+// Copyright 2020 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "src/ast/null_literal.h"
+
+#include "gtest/gtest.h"
+#include "src/ast/type/i32_type.h"
+
+namespace tint {
+namespace ast {
+namespace {
+
+using NullLiteralTest = testing::Test;
+
+TEST_F(NullLiteralTest, Is) {
+  ast::type::I32Type i32;
+  NullLiteral i{&i32};
+  EXPECT_FALSE(i.IsBool());
+  EXPECT_FALSE(i.IsInt());
+  EXPECT_FALSE(i.IsFloat());
+  EXPECT_FALSE(i.IsUint());
+  EXPECT_TRUE(i.IsNull());
+}
+
+TEST_F(NullLiteralTest, ToStr) {
+  ast::type::I32Type i32;
+  NullLiteral i{&i32};
+
+  EXPECT_EQ(i.to_str(), "null __i32");
+}
+
+TEST_F(NullLiteralTest, Name_I32) {
+  ast::type::I32Type i32;
+  NullLiteral i{&i32};
+  EXPECT_EQ("__null__i32", i.name());
+}
+
+}  // namespace
+}  // namespace ast
+}  // namespace tint
\ No newline at end of file
diff --git a/src/ast/uint_literal_test.cc b/src/ast/uint_literal_test.cc
index a1402b3c44..841ad2253d 100644
--- a/src/ast/uint_literal_test.cc
+++ b/src/ast/uint_literal_test.cc
@@ -37,6 +37,7 @@ TEST_F(UintLiteralTest, Is) {
   EXPECT_FALSE(u.IsInt());
   EXPECT_FALSE(u.IsFloat());
   EXPECT_TRUE(u.IsUint());
+  EXPECT_FALSE(u.IsNull());
 }
 
 TEST_F(UintLiteralTest, ToStr) {
diff --git a/src/writer/spirv/builder.cc b/src/writer/spirv/builder.cc
index 1bfb0ad5e2..9c1094d8ed 100644
--- a/src/writer/spirv/builder.cc
+++ b/src/writer/spirv/builder.cc
@@ -36,6 +36,7 @@
 #include "src/ast/location_decoration.h"
 #include "src/ast/loop_statement.h"
 #include "src/ast/member_accessor_expression.h"
+#include "src/ast/null_literal.h"
 #include "src/ast/return_statement.h"
 #include "src/ast/scalar_constructor_expression.h"
 #include "src/ast/set_decoration.h"
@@ -430,9 +431,15 @@ bool Builder::GenerateFunctionVariable(ast::Variable* var) {
 
   // TODO(dsinclair) We could detect if the constructor is fully const and emit
   // an initializer value for the variable instead of doing the OpLoad.
+  ast::NullLiteral nl(var->type()->UnwrapPtrIfNeeded());
+  auto null_id = GenerateLiteralIfNeeded(&nl);
+  if (null_id == 0) {
+    return 0;
+  }
+  push_function_var({Operand::Int(type_id), result,
+                     Operand::Int(ConvertStorageClass(sc)),
+                     Operand::Int(null_id)});
 
-  push_function_var(
-      {Operand::Int(type_id), result, Operand::Int(ConvertStorageClass(sc))});
   if (var->has_constructor()) {
     init_id = GenerateLoadIfNeeded(var->constructor()->result_type(), init_id);
     GenerateStore(var_id, init_id);
@@ -493,6 +500,19 @@ bool Builder::GenerateGlobalVariable(ast::Variable* var) {
                               Operand::Int(ConvertStorageClass(sc))};
   if (var->has_constructor()) {
     ops.push_back(Operand::Int(init_id));
+  } else {
+    // If we don't have a constructor and we're an Output or Private variable
+    // then WGSL requires an initializer.
+    if (var->storage_class() == ast::StorageClass::kPrivate ||
+        var->storage_class() == ast::StorageClass::kNone ||
+        var->storage_class() == ast::StorageClass::kOutput) {
+      ast::NullLiteral nl(var->type()->UnwrapPtrIfNeeded());
+      init_id = GenerateLiteralIfNeeded(&nl);
+      if (init_id == 0) {
+        return 0;
+      }
+      ops.push_back(Operand::Int(init_id));
+    }
   }
 
   push_type(spv::Op::OpVariable, std::move(ops));
@@ -965,6 +985,8 @@ uint32_t Builder::GenerateLiteralIfNeeded(ast::Literal* lit) {
   } else if (lit->IsFloat()) {
     push_type(spv::Op::OpConstant, {Operand::Int(type_id), result,
                                     Operand::Float(lit->AsFloat()->value())});
+  } else if (lit->IsNull()) {
+    push_type(spv::Op::OpConstantNull, {Operand::Int(type_id), result});
   } else {
     error_ = "unknown literal type";
     return 0;
diff --git a/src/writer/spirv/builder_accessor_expression_test.cc b/src/writer/spirv/builder_accessor_expression_test.cc
index 182110fd23..d96554e75f 100644
--- a/src/writer/spirv/builder_accessor_expression_test.cc
+++ b/src/writer/spirv/builder_accessor_expression_test.cc
@@ -68,20 +68,21 @@ TEST_F(BuilderTest, ArrayAccessor) {
   b.push_function(Function{});
   ASSERT_TRUE(b.GenerateFunctionVariable(&var)) << b.error();
 
-  EXPECT_EQ(b.GenerateAccessorExpression(&expr), 8u);
+  EXPECT_EQ(b.GenerateAccessorExpression(&expr), 9u);
 
   EXPECT_EQ(DumpInstructions(b.types()), R"(%4 = OpTypeFloat 32
 %3 = OpTypeVector %4 3
 %2 = OpTypePointer Function %3
-%5 = OpTypeInt 32 1
-%6 = OpConstant %5 1
-%7 = OpTypePointer Function %4
+%5 = OpConstantNull %3
+%6 = OpTypeInt 32 1
+%7 = OpConstant %6 1
+%8 = OpTypePointer Function %4
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].variables()),
-            R"(%1 = OpVariable %2 Function
+            R"(%1 = OpVariable %2 Function %5
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
-            R"(%8 = OpAccessChain %7 %1 %6
+            R"(%9 = OpAccessChain %8 %1 %7
 )");
 }
 
@@ -114,22 +115,24 @@ TEST_F(BuilderTest, Accessor_Array_LoadIndex) {
   ASSERT_TRUE(b.GenerateFunctionVariable(&var)) << b.error();
   ASSERT_TRUE(b.GenerateFunctionVariable(&idx)) << b.error();
 
-  EXPECT_EQ(b.GenerateAccessorExpression(&expr), 10u);
+  EXPECT_EQ(b.GenerateAccessorExpression(&expr), 12u);
 
   EXPECT_EQ(DumpInstructions(b.types()), R"(%4 = OpTypeFloat 32
 %3 = OpTypeVector %4 3
 %2 = OpTypePointer Function %3
-%7 = OpTypeInt 32 1
-%6 = OpTypePointer Function %7
-%9 = OpTypePointer Function %4
+%5 = OpConstantNull %3
+%8 = OpTypeInt 32 1
+%7 = OpTypePointer Function %8
+%9 = OpConstantNull %8
+%11 = OpTypePointer Function %4
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].variables()),
-            R"(%1 = OpVariable %2 Function
-%5 = OpVariable %6 Function
+            R"(%1 = OpVariable %2 Function %5
+%6 = OpVariable %7 Function %9
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
-            R"(%8 = OpLoad %7 %5
-%10 = OpAccessChain %9 %1 %8
+            R"(%10 = OpLoad %8 %6
+%12 = OpAccessChain %11 %1 %10
 )");
 }
 
@@ -163,22 +166,23 @@ TEST_F(BuilderTest, ArrayAccessor_Dynamic) {
   b.push_function(Function{});
   ASSERT_TRUE(b.GenerateFunctionVariable(&var)) << b.error();
 
-  EXPECT_EQ(b.GenerateAccessorExpression(&expr), 10u);
+  EXPECT_EQ(b.GenerateAccessorExpression(&expr), 11u);
 
   EXPECT_EQ(DumpInstructions(b.types()), R"(%4 = OpTypeFloat 32
 %3 = OpTypeVector %4 3
 %2 = OpTypePointer Function %3
-%5 = OpTypeInt 32 1
-%6 = OpConstant %5 1
-%7 = OpConstant %5 2
-%9 = OpTypePointer Function %4
+%5 = OpConstantNull %3
+%6 = OpTypeInt 32 1
+%7 = OpConstant %6 1
+%8 = OpConstant %6 2
+%10 = OpTypePointer Function %4
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].variables()),
-            R"(%1 = OpVariable %2 Function
+            R"(%1 = OpVariable %2 Function %5
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
-            R"(%8 = OpIAdd %5 %6 %7
-%10 = OpAccessChain %9 %1 %8
+            R"(%9 = OpIAdd %6 %7 %8
+%11 = OpAccessChain %10 %1 %9
 )");
 }
 
@@ -211,7 +215,7 @@ TEST_F(BuilderTest, ArrayAccessor_MultiLevel) {
   b.push_function(Function{});
   ASSERT_TRUE(b.GenerateFunctionVariable(&var)) << b.error();
 
-  EXPECT_EQ(b.GenerateAccessorExpression(&expr), 12u);
+  EXPECT_EQ(b.GenerateAccessorExpression(&expr), 13u);
 
   EXPECT_EQ(DumpInstructions(b.types()), R"(%5 = OpTypeFloat 32
 %4 = OpTypeVector %5 3
@@ -219,16 +223,17 @@ TEST_F(BuilderTest, ArrayAccessor_MultiLevel) {
 %7 = OpConstant %6 4
 %3 = OpTypeArray %4 %7
 %2 = OpTypePointer Function %3
-%8 = OpTypeInt 32 1
-%9 = OpConstant %8 3
-%10 = OpConstant %8 2
-%11 = OpTypePointer Function %5
+%8 = OpConstantNull %3
+%9 = OpTypeInt 32 1
+%10 = OpConstant %9 3
+%11 = OpConstant %9 2
+%12 = OpTypePointer Function %5
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].variables()),
-            R"(%1 = OpVariable %2 Function
+            R"(%1 = OpVariable %2 Function %8
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
-            R"(%12 = OpAccessChain %11 %1 %9 %10
+            R"(%13 = OpAccessChain %12 %1 %10 %11
 )");
 }
 
@@ -259,7 +264,7 @@ TEST_F(BuilderTest, Accessor_ArrayWithSwizzle) {
   Builder b(&mod);
   b.push_function(Function{});
   ASSERT_TRUE(b.GenerateFunctionVariable(&var)) << b.error();
-  EXPECT_EQ(b.GenerateAccessorExpression(&expr), 14u);
+  EXPECT_EQ(b.GenerateAccessorExpression(&expr), 15u);
 
   EXPECT_EQ(DumpInstructions(b.types()), R"(%5 = OpTypeFloat 32
 %4 = OpTypeVector %5 3
@@ -267,18 +272,19 @@ TEST_F(BuilderTest, Accessor_ArrayWithSwizzle) {
 %7 = OpConstant %6 4
 %3 = OpTypeArray %4 %7
 %2 = OpTypePointer Function %3
-%8 = OpTypeInt 32 1
-%9 = OpConstant %8 2
-%10 = OpTypePointer Function %4
-%12 = OpTypeVector %5 2
+%8 = OpConstantNull %3
+%9 = OpTypeInt 32 1
+%10 = OpConstant %9 2
+%11 = OpTypePointer Function %4
+%13 = OpTypeVector %5 2
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].variables()),
-            R"(%1 = OpVariable %2 Function
+            R"(%1 = OpVariable %2 Function %8
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
-            R"(%11 = OpAccessChain %10 %1 %9
-%13 = OpLoad %4 %11
-%14 = OpVectorShuffle %12 %13 %13 0 1
+            R"(%12 = OpAccessChain %11 %1 %10
+%14 = OpLoad %4 %12
+%15 = OpVectorShuffle %13 %14 %14 0 1
 )");
 }
 
@@ -320,20 +326,21 @@ TEST_F(BuilderTest, MemberAccessor) {
   b.push_function(Function{});
   ASSERT_TRUE(b.GenerateFunctionVariable(&var)) << b.error();
 
-  EXPECT_EQ(b.GenerateAccessorExpression(&expr), 8u);
+  EXPECT_EQ(b.GenerateAccessorExpression(&expr), 9u);
 
   EXPECT_EQ(DumpInstructions(b.types()), R"(%4 = OpTypeFloat 32
 %3 = OpTypeStruct %4 %4
 %2 = OpTypePointer Function %3
-%5 = OpTypeInt 32 0
-%6 = OpConstant %5 1
-%7 = OpTypePointer Function %4
+%5 = OpConstantNull %3
+%6 = OpTypeInt 32 0
+%7 = OpConstant %6 1
+%8 = OpTypePointer Function %4
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].variables()),
-            R"(%1 = OpVariable %2 Function
+            R"(%1 = OpVariable %2 Function %5
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
-            R"(%8 = OpAccessChain %7 %1 %6
+            R"(%9 = OpAccessChain %8 %1 %7
 )");
 }
 
@@ -385,21 +392,22 @@ TEST_F(BuilderTest, MemberAccessor_Nested) {
   b.push_function(Function{});
   ASSERT_TRUE(b.GenerateFunctionVariable(&var)) << b.error();
 
-  EXPECT_EQ(b.GenerateAccessorExpression(&expr), 9u);
+  EXPECT_EQ(b.GenerateAccessorExpression(&expr), 10u);
 
   EXPECT_EQ(DumpInstructions(b.types()), R"(%5 = OpTypeFloat 32
 %4 = OpTypeStruct %5 %5
 %3 = OpTypeStruct %4
 %2 = OpTypePointer Function %3
-%6 = OpTypeInt 32 0
-%7 = OpConstant %6 0
-%8 = OpTypePointer Function %5
+%6 = OpConstantNull %3
+%7 = OpTypeInt 32 0
+%8 = OpConstant %7 0
+%9 = OpTypePointer Function %5
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].variables()),
-            R"(%1 = OpVariable %2 Function
+            R"(%1 = OpVariable %2 Function %6
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
-            R"(%9 = OpAccessChain %8 %1 %7 %7
+            R"(%10 = OpAccessChain %9 %1 %8 %8
 )");
 }
 
@@ -454,21 +462,22 @@ TEST_F(BuilderTest, MemberAccessor_Nested_WithAlias) {
   b.push_function(Function{});
   ASSERT_TRUE(b.GenerateFunctionVariable(&var)) << b.error();
 
-  EXPECT_EQ(b.GenerateAccessorExpression(&expr), 9u);
+  EXPECT_EQ(b.GenerateAccessorExpression(&expr), 10u);
 
   EXPECT_EQ(DumpInstructions(b.types()), R"(%5 = OpTypeFloat 32
 %4 = OpTypeStruct %5 %5
 %3 = OpTypeStruct %4
 %2 = OpTypePointer Function %3
-%6 = OpTypeInt 32 0
-%7 = OpConstant %6 0
-%8 = OpTypePointer Function %5
+%6 = OpConstantNull %3
+%7 = OpTypeInt 32 0
+%8 = OpConstant %7 0
+%9 = OpTypePointer Function %5
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].variables()),
-            R"(%1 = OpVariable %2 Function
+            R"(%1 = OpVariable %2 Function %6
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
-            R"(%9 = OpAccessChain %8 %1 %7 %7
+            R"(%10 = OpAccessChain %9 %1 %8 %8
 )");
 }
 
@@ -532,17 +541,18 @@ TEST_F(BuilderTest, MemberAccessor_Nested_Assignment_LHS) {
 %4 = OpTypeStruct %5 %5
 %3 = OpTypeStruct %4
 %2 = OpTypePointer Function %3
-%6 = OpTypeInt 32 0
-%7 = OpConstant %6 0
-%8 = OpTypePointer Function %5
-%10 = OpConstant %5 2
+%6 = OpConstantNull %3
+%7 = OpTypeInt 32 0
+%8 = OpConstant %7 0
+%9 = OpTypePointer Function %5
+%11 = OpConstant %5 2
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].variables()),
-            R"(%1 = OpVariable %2 Function
+            R"(%1 = OpVariable %2 Function %6
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
-            R"(%9 = OpAccessChain %8 %1 %7 %7
-OpStore %9 %10
+            R"(%10 = OpAccessChain %9 %1 %8 %8
+OpStore %10 %11
 )");
 }
 
@@ -608,18 +618,20 @@ TEST_F(BuilderTest, MemberAccessor_Nested_Assignment_RHS) {
 %4 = OpTypeStruct %5 %5
 %3 = OpTypeStruct %4
 %2 = OpTypePointer Function %3
-%7 = OpTypePointer Function %5
-%8 = OpTypeInt 32 0
-%9 = OpConstant %8 0
+%6 = OpConstantNull %3
+%8 = OpTypePointer Function %5
+%9 = OpConstantNull %5
+%10 = OpTypeInt 32 0
+%11 = OpConstant %10 0
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].variables()),
-            R"(%1 = OpVariable %2 Function
-%6 = OpVariable %7 Function
+            R"(%1 = OpVariable %2 Function %6
+%7 = OpVariable %8 Function %9
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
-            R"(%10 = OpAccessChain %7 %1 %9 %9
-%11 = OpLoad %5 %10
-OpStore %6 %11
+            R"(%12 = OpAccessChain %8 %1 %11 %11
+%13 = OpLoad %5 %12
+OpStore %7 %13
 )");
 }
 
@@ -645,20 +657,21 @@ TEST_F(BuilderTest, MemberAccessor_Swizzle_Single) {
   b.push_function(Function{});
   ASSERT_TRUE(b.GenerateFunctionVariable(&var)) << b.error();
 
-  EXPECT_EQ(b.GenerateAccessorExpression(&expr), 8u);
+  EXPECT_EQ(b.GenerateAccessorExpression(&expr), 9u);
 
   EXPECT_EQ(DumpInstructions(b.types()), R"(%4 = OpTypeFloat 32
 %3 = OpTypeVector %4 3
 %2 = OpTypePointer Function %3
-%5 = OpTypeInt 32 0
-%6 = OpConstant %5 1
-%7 = OpTypePointer Function %4
+%5 = OpConstantNull %3
+%6 = OpTypeInt 32 0
+%7 = OpConstant %6 1
+%8 = OpTypePointer Function %4
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].variables()),
-            R"(%1 = OpVariable %2 Function
+            R"(%1 = OpVariable %2 Function %5
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
-            R"(%8 = OpAccessChain %7 %1 %6
+            R"(%9 = OpAccessChain %8 %1 %7
 )");
 }
 
@@ -684,19 +697,20 @@ TEST_F(BuilderTest, MemberAccessor_Swizzle_MultipleNames) {
   b.push_function(Function{});
   ASSERT_TRUE(b.GenerateFunctionVariable(&var)) << b.error();
 
-  EXPECT_EQ(b.GenerateAccessorExpression(&expr), 7u);
+  EXPECT_EQ(b.GenerateAccessorExpression(&expr), 8u);
 
   EXPECT_EQ(DumpInstructions(b.types()), R"(%4 = OpTypeFloat 32
 %3 = OpTypeVector %4 3
 %2 = OpTypePointer Function %3
-%5 = OpTypeVector %4 2
+%5 = OpConstantNull %3
+%6 = OpTypeVector %4 2
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].variables()),
-            R"(%1 = OpVariable %2 Function
+            R"(%1 = OpVariable %2 Function %5
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
-            R"(%6 = OpLoad %3 %1
-%7 = OpVectorShuffle %5 %6 %6 1 0
+            R"(%7 = OpLoad %3 %1
+%8 = OpVectorShuffle %6 %7 %7 1 0
 )");
 }
 
@@ -724,20 +738,21 @@ TEST_F(BuilderTest, MemberAccessor_Swizzle_of_Swizzle) {
   b.push_function(Function{});
   ASSERT_TRUE(b.GenerateFunctionVariable(&var)) << b.error();
 
-  EXPECT_EQ(b.GenerateAccessorExpression(&expr), 8u);
+  EXPECT_EQ(b.GenerateAccessorExpression(&expr), 9u);
 
   EXPECT_EQ(DumpInstructions(b.types()), R"(%4 = OpTypeFloat 32
 %3 = OpTypeVector %4 3
 %2 = OpTypePointer Function %3
-%7 = OpTypeVector %4 2
+%5 = OpConstantNull %3
+%8 = OpTypeVector %4 2
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].variables()),
-            R"(%1 = OpVariable %2 Function
+            R"(%1 = OpVariable %2 Function %5
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
-            R"(%5 = OpLoad %3 %1
-%6 = OpVectorShuffle %3 %5 %5 1 0 2
-%8 = OpVectorShuffle %7 %6 %6 0 2
+            R"(%6 = OpLoad %3 %1
+%7 = OpVectorShuffle %3 %6 %6 1 0 2
+%9 = OpVectorShuffle %8 %7 %7 0 2
 )");
 }
 
@@ -765,19 +780,20 @@ TEST_F(BuilderTest, MemberAccessor_Member_of_Swizzle) {
   b.push_function(Function{});
   ASSERT_TRUE(b.GenerateFunctionVariable(&var)) << b.error();
 
-  EXPECT_EQ(b.GenerateAccessorExpression(&expr), 7u);
+  EXPECT_EQ(b.GenerateAccessorExpression(&expr), 8u);
 
   EXPECT_EQ(DumpInstructions(b.types()), R"(%4 = OpTypeFloat 32
 %3 = OpTypeVector %4 3
 %2 = OpTypePointer Function %3
+%5 = OpConstantNull %3
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].variables()),
-            R"(%1 = OpVariable %2 Function
+            R"(%1 = OpVariable %2 Function %5
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
-            R"(%5 = OpLoad %3 %1
-%6 = OpVectorShuffle %3 %5 %5 1 0 2
-%7 = OpCompositeExtract %4 %6 0
+            R"(%6 = OpLoad %3 %1
+%7 = OpVectorShuffle %3 %6 %6 1 0 2
+%8 = OpCompositeExtract %4 %7 0
 )");
 }
 
@@ -807,21 +823,22 @@ TEST_F(BuilderTest, MemberAccessor_Array_of_Swizzle) {
   b.push_function(Function{});
   ASSERT_TRUE(b.GenerateFunctionVariable(&var)) << b.error();
 
-  EXPECT_EQ(b.GenerateAccessorExpression(&expr), 9u);
+  EXPECT_EQ(b.GenerateAccessorExpression(&expr), 10u);
 
   EXPECT_EQ(DumpInstructions(b.types()), R"(%4 = OpTypeFloat 32
 %3 = OpTypeVector %4 3
 %2 = OpTypePointer Function %3
-%7 = OpTypeInt 32 1
-%8 = OpConstant %7 1
+%5 = OpConstantNull %3
+%8 = OpTypeInt 32 1
+%9 = OpConstant %8 1
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].variables()),
-            R"(%1 = OpVariable %2 Function
+            R"(%1 = OpVariable %2 Function %5
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
-            R"(%5 = OpLoad %3 %1
-%6 = OpVectorShuffle %3 %5 %5 1 0 2
-%9 = OpVectorExtractDynamic %4 %6 %8
+            R"(%6 = OpLoad %3 %1
+%7 = OpVectorShuffle %3 %6 %6 1 0 2
+%10 = OpVectorExtractDynamic %4 %7 %9
 )");
 }
 
@@ -897,7 +914,7 @@ TEST_F(BuilderTest, Accessor_Mixed_ArrayAndMember) {
   b.push_function(Function{});
   ASSERT_TRUE(b.GenerateFunctionVariable(&var)) << b.error();
 
-  EXPECT_EQ(b.GenerateAccessorExpression(&expr), 21u);
+  EXPECT_EQ(b.GenerateAccessorExpression(&expr), 22u);
 
   EXPECT_EQ(DumpInstructions(b.types()), R"(%9 = OpTypeFloat 32
 %8 = OpTypeVector %9 3
@@ -910,20 +927,21 @@ TEST_F(BuilderTest, Accessor_Mixed_ArrayAndMember) {
 %12 = OpConstant %10 2
 %3 = OpTypeArray %4 %12
 %2 = OpTypePointer Function %3
-%13 = OpTypeInt 32 1
-%14 = OpConstant %13 0
-%15 = OpConstant %10 0
-%16 = OpConstant %13 2
-%17 = OpTypePointer Function %8
-%19 = OpTypeVector %9 2
+%13 = OpConstantNull %3
+%14 = OpTypeInt 32 1
+%15 = OpConstant %14 0
+%16 = OpConstant %10 0
+%17 = OpConstant %14 2
+%18 = OpTypePointer Function %8
+%20 = OpTypeVector %9 2
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].variables()),
-            R"(%1 = OpVariable %2 Function
+            R"(%1 = OpVariable %2 Function %13
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
-            R"(%18 = OpAccessChain %17 %1 %14 %15 %16 %15 %15
-%20 = OpLoad %8 %18
-%21 = OpVectorShuffle %19 %20 %20 1 0
+            R"(%19 = OpAccessChain %18 %1 %15 %16 %17 %16 %16
+%21 = OpLoad %8 %19
+%22 = OpVectorShuffle %20 %21 %21 1 0
 )");
 }
 
diff --git a/src/writer/spirv/builder_assign_test.cc b/src/writer/spirv/builder_assign_test.cc
index 7847d065b6..3c5467780d 100644
--- a/src/writer/spirv/builder_assign_test.cc
+++ b/src/writer/spirv/builder_assign_test.cc
@@ -69,11 +69,12 @@ TEST_F(BuilderTest, Assign_Var) {
 
   EXPECT_EQ(DumpInstructions(b.types()), R"(%3 = OpTypeFloat 32
 %2 = OpTypePointer Output %3
-%1 = OpVariable %2 Output
-%4 = OpConstant %3 1
+%4 = OpConstantNull %3
+%1 = OpVariable %2 Output %4
+%5 = OpConstant %3 1
 )");
 
-  EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()), R"(OpStore %1 %4
+  EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()), R"(OpStore %1 %5
 )");
 }
 
@@ -180,13 +181,14 @@ TEST_F(BuilderTest, Assign_Vector) {
   EXPECT_EQ(DumpInstructions(b.types()), R"(%4 = OpTypeFloat 32
 %3 = OpTypeVector %4 3
 %2 = OpTypePointer Output %3
-%1 = OpVariable %2 Output
-%5 = OpConstant %4 1
-%6 = OpConstant %4 3
-%7 = OpConstantComposite %3 %5 %5 %6
+%5 = OpConstantNull %3
+%1 = OpVariable %2 Output %5
+%6 = OpConstant %4 1
+%7 = OpConstant %4 3
+%8 = OpConstantComposite %3 %6 %6 %7
 )");
 
-  EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()), R"(OpStore %1 %7
+  EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()), R"(OpStore %1 %8
 )");
 }
 
@@ -224,16 +226,17 @@ TEST_F(BuilderTest, Assign_Vector_MemberByName) {
   EXPECT_EQ(DumpInstructions(b.types()), R"(%4 = OpTypeFloat 32
 %3 = OpTypeVector %4 3
 %2 = OpTypePointer Output %3
-%1 = OpVariable %2 Output
-%5 = OpTypeInt 32 0
-%6 = OpConstant %5 1
-%7 = OpTypePointer Output %4
-%9 = OpConstant %4 1
+%5 = OpConstantNull %3
+%1 = OpVariable %2 Output %5
+%6 = OpTypeInt 32 0
+%7 = OpConstant %6 1
+%8 = OpTypePointer Output %4
+%10 = OpConstant %4 1
 )");
 
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
-            R"(%8 = OpAccessChain %7 %1 %6
-OpStore %8 %9
+            R"(%9 = OpAccessChain %8 %1 %7
+OpStore %9 %10
 )");
 }
 
@@ -273,16 +276,17 @@ TEST_F(BuilderTest, Assign_Vector_MemberByIndex) {
   EXPECT_EQ(DumpInstructions(b.types()), R"(%4 = OpTypeFloat 32
 %3 = OpTypeVector %4 3
 %2 = OpTypePointer Output %3
-%1 = OpVariable %2 Output
-%5 = OpTypeInt 32 1
-%6 = OpConstant %5 1
-%7 = OpTypePointer Output %4
-%9 = OpConstant %4 1
+%5 = OpConstantNull %3
+%1 = OpVariable %2 Output %5
+%6 = OpTypeInt 32 1
+%7 = OpConstant %6 1
+%8 = OpTypePointer Output %4
+%10 = OpConstant %4 1
 )");
 
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
-            R"(%8 = OpAccessChain %7 %1 %6
-OpStore %8 %9
+            R"(%9 = OpAccessChain %8 %1 %7
+OpStore %9 %10
 )");
 }
 
diff --git a/src/writer/spirv/builder_call_test.cc b/src/writer/spirv/builder_call_test.cc
index ea4dd9533a..d9aaef2114 100644
--- a/src/writer/spirv/builder_call_test.cc
+++ b/src/writer/spirv/builder_call_test.cc
@@ -107,19 +107,20 @@ TEST_F(BuilderTest, Call_GLSLMethod_WithLoad) {
   ASSERT_TRUE(b.GenerateGlobalVariable(var.get())) << b.error();
   ASSERT_TRUE(b.GenerateFunction(&func)) << b.error();
 
-  EXPECT_EQ(b.GenerateCallExpression(&expr), 9u) << b.error();
+  EXPECT_EQ(b.GenerateCallExpression(&expr), 10u) << b.error();
   EXPECT_EQ(DumpBuilder(b), R"(%1 = OpExtInstImport "GLSL.std.450"
 OpName %2 "ident"
-OpName %7 "a_func"
+OpName %8 "a_func"
 %4 = OpTypeFloat 32
 %3 = OpTypePointer Private %4
-%2 = OpVariable %3 Private
-%6 = OpTypeVoid
-%5 = OpTypeFunction %6
-%7 = OpFunction %6 None %5
-%8 = OpLabel
-%10 = OpLoad %4 %2
-%9 = OpExtInst %4 %1 Round %10
+%5 = OpConstantNull %4
+%2 = OpVariable %3 Private %5
+%7 = OpTypeVoid
+%6 = OpTypeFunction %7
+%8 = OpFunction %7 None %6
+%9 = OpLabel
+%11 = OpLoad %4 %2
+%10 = OpExtInst %4 %1 Round %11
 OpFunctionEnd
 )");
 }
diff --git a/src/writer/spirv/builder_cast_expression_test.cc b/src/writer/spirv/builder_cast_expression_test.cc
index 90ca156542..c6b6fcb88d 100644
--- a/src/writer/spirv/builder_cast_expression_test.cc
+++ b/src/writer/spirv/builder_cast_expression_test.cc
@@ -86,16 +86,17 @@ TEST_F(BuilderTest, Cast_WithLoad) {
   Builder b(&mod);
   b.push_function(Function{});
   ASSERT_TRUE(b.GenerateGlobalVariable(var.get())) << b.error();
-  EXPECT_EQ(b.GenerateCastExpression(&cast), 4u) << b.error();
+  EXPECT_EQ(b.GenerateCastExpression(&cast), 5u) << b.error();
 
   EXPECT_EQ(DumpInstructions(b.types()), R"(%3 = OpTypeInt 32 1
 %2 = OpTypePointer Private %3
-%1 = OpVariable %2 Private
-%5 = OpTypeFloat 32
+%4 = OpConstantNull %3
+%1 = OpVariable %2 Private %4
+%6 = OpTypeFloat 32
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
-            R"(%6 = OpLoad %3 %1
-%4 = OpConvertSToF %5 %6
+            R"(%7 = OpLoad %3 %1
+%5 = OpConvertSToF %6 %7
 )");
 }
 
diff --git a/src/writer/spirv/builder_constructor_expression_test.cc b/src/writer/spirv/builder_constructor_expression_test.cc
index b7af4c88f7..df0c21905e 100644
--- a/src/writer/spirv/builder_constructor_expression_test.cc
+++ b/src/writer/spirv/builder_constructor_expression_test.cc
@@ -106,21 +106,22 @@ TEST_F(BuilderTest, Constructor_Type_NonConstructorParam) {
   b.push_function(Function{});
   ASSERT_TRUE(b.GenerateFunctionVariable(var.get())) << b.error();
 
-  EXPECT_EQ(b.GenerateConstructorExpression(&t, false), 7u);
+  EXPECT_EQ(b.GenerateConstructorExpression(&t, false), 8u);
   ASSERT_FALSE(b.has_error()) << b.error();
 
   EXPECT_EQ(DumpInstructions(b.types()), R"(%3 = OpTypeFloat 32
 %2 = OpTypePointer Function %3
-%4 = OpTypeVector %3 2
-%5 = OpConstant %3 1
+%4 = OpConstantNull %3
+%5 = OpTypeVector %3 2
+%6 = OpConstant %3 1
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].variables()),
-            R"(%1 = OpVariable %2 Function
+            R"(%1 = OpVariable %2 Function %4
 )");
 
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
-            R"(%6 = OpLoad %3 %1
-%7 = OpCompositeConstruct %4 %5 %6
+            R"(%7 = OpLoad %3 %1
+%8 = OpCompositeConstruct %5 %6 %7
 )");
 }
 
@@ -151,24 +152,25 @@ TEST_F(BuilderTest, Constructor_Type_NonConstVector) {
   b.push_function(Function{});
   ASSERT_TRUE(b.GenerateFunctionVariable(var.get())) << b.error();
 
-  EXPECT_EQ(b.GenerateConstructorExpression(&t, false), 10u);
+  EXPECT_EQ(b.GenerateConstructorExpression(&t, false), 11u);
   ASSERT_FALSE(b.has_error()) << b.error();
 
   EXPECT_EQ(DumpInstructions(b.types()), R"(%4 = OpTypeFloat 32
 %3 = OpTypeVector %4 2
 %2 = OpTypePointer Function %3
-%5 = OpTypeVector %4 4
-%6 = OpConstant %4 1
+%5 = OpConstantNull %3
+%6 = OpTypeVector %4 4
+%7 = OpConstant %4 1
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].variables()),
-            R"(%1 = OpVariable %2 Function
+            R"(%1 = OpVariable %2 Function %5
 )");
 
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
-            R"(%7 = OpLoad %3 %1
-%8 = OpCompositeExtract %4 %7 0
-%9 = OpCompositeExtract %4 %7 1
-%10 = OpCompositeConstruct %5 %6 %6 %8 %9
+            R"(%8 = OpLoad %3 %1
+%9 = OpCompositeExtract %4 %8 0
+%10 = OpCompositeExtract %4 %8 1
+%11 = OpCompositeConstruct %6 %7 %7 %9 %10
 )");
 }
 
diff --git a/src/writer/spirv/builder_entry_point_test.cc b/src/writer/spirv/builder_entry_point_test.cc
index 2c4a71bafc..ae55071b25 100644
--- a/src/writer/spirv/builder_entry_point_test.cc
+++ b/src/writer/spirv/builder_entry_point_test.cc
@@ -129,15 +129,16 @@ TEST_F(BuilderTest, EntryPoint_WithInterfaceIds) {
   ASSERT_TRUE(b.GenerateEntryPoint(&ep));
   EXPECT_EQ(DumpInstructions(b.debug()), R"(OpName %1 "my_in"
 OpName %4 "my_out"
-OpName %6 "my_wg"
+OpName %7 "my_wg"
 )");
   EXPECT_EQ(DumpInstructions(b.types()), R"(%3 = OpTypeFloat 32
 %2 = OpTypePointer Input %3
 %1 = OpVariable %2 Input
 %5 = OpTypePointer Output %3
-%4 = OpVariable %5 Output
-%7 = OpTypePointer Workgroup %3
-%6 = OpVariable %7 Workgroup
+%6 = OpConstantNull %3
+%4 = OpVariable %5 Output %6
+%8 = OpTypePointer Workgroup %3
+%7 = OpVariable %8 Workgroup
 )");
   EXPECT_EQ(DumpInstructions(b.preamble()),
             R"(OpEntryPoint Vertex %3 "main" %1 %4
diff --git a/src/writer/spirv/builder_function_variable_test.cc b/src/writer/spirv/builder_function_variable_test.cc
index 0917616671..e462ce1601 100644
--- a/src/writer/spirv/builder_function_variable_test.cc
+++ b/src/writer/spirv/builder_function_variable_test.cc
@@ -54,10 +54,12 @@ TEST_F(BuilderTest, FunctionVar_NoStorageClass) {
 )");
   EXPECT_EQ(DumpInstructions(b.types()), R"(%3 = OpTypeFloat 32
 %2 = OpTypePointer Function %3
+%4 = OpConstantNull %3
 )");
 
   const auto& func = b.functions()[0];
-  EXPECT_EQ(DumpInstructions(func.variables()), R"(%1 = OpVariable %2 Function
+  EXPECT_EQ(DumpInstructions(func.variables()),
+            R"(%1 = OpVariable %2 Function %4
 )");
 }
 
@@ -99,9 +101,10 @@ TEST_F(BuilderTest, FunctionVar_WithConstantConstructor) {
 %4 = OpConstant %2 3
 %5 = OpConstantComposite %1 %3 %3 %4
 %7 = OpTypePointer Function %2
+%8 = OpConstantNull %2
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].variables()),
-            R"(%6 = OpVariable %7 Function
+            R"(%6 = OpVariable %7 Function %8
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()), R"(OpStore %6 %5
 )");
@@ -147,9 +150,10 @@ TEST_F(BuilderTest, FunctionVar_WithNonConstantConstructor) {
 %3 = OpConstant %2 1
 %4 = OpConstant %2 3
 %8 = OpTypePointer Function %1
+%9 = OpConstantNull %1
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].variables()),
-            R"(%7 = OpVariable %8 Function
+            R"(%7 = OpVariable %8 Function %9
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
             R"(%5 = OpFAdd %2 %4 %4
diff --git a/src/writer/spirv/builder_global_variable_test.cc b/src/writer/spirv/builder_global_variable_test.cc
index dd40711b6a..306d2d6f49 100644
--- a/src/writer/spirv/builder_global_variable_test.cc
+++ b/src/writer/spirv/builder_global_variable_test.cc
@@ -52,7 +52,8 @@ TEST_F(BuilderTest, GlobalVar_NoStorageClass) {
 )");
   EXPECT_EQ(DumpInstructions(b.types()), R"(%3 = OpTypeFloat 32
 %2 = OpTypePointer Private %3
-%1 = OpVariable %2 Private
+%4 = OpConstantNull %3
+%1 = OpVariable %2 Private %4
 )");
 }
 
@@ -67,7 +68,23 @@ TEST_F(BuilderTest, GlobalVar_WithStorageClass) {
 )");
   EXPECT_EQ(DumpInstructions(b.types()), R"(%3 = OpTypeFloat 32
 %2 = OpTypePointer Output %3
-%1 = OpVariable %2 Output
+%4 = OpConstantNull %3
+%1 = OpVariable %2 Output %4
+)");
+}
+
+TEST_F(BuilderTest, GlobalVar_WithStorageClass_Input) {
+  ast::type::F32Type f32;
+  ast::Variable v("var", ast::StorageClass::kInput, &f32);
+
+  ast::Module mod;
+  Builder b(&mod);
+  EXPECT_TRUE(b.GenerateGlobalVariable(&v)) << b.error();
+  EXPECT_EQ(DumpInstructions(b.debug()), R"(OpName %1 "var"
+)");
+  EXPECT_EQ(DumpInstructions(b.types()), R"(%3 = OpTypeFloat 32
+%2 = OpTypePointer Input %3
+%1 = OpVariable %2 Input
 )");
 }
 
@@ -167,7 +184,8 @@ TEST_F(BuilderTest, GlobalVar_WithLocation) {
 )");
   EXPECT_EQ(DumpInstructions(b.types()), R"(%3 = OpTypeFloat 32
 %2 = OpTypePointer Output %3
-%1 = OpVariable %2 Output
+%4 = OpConstantNull %3
+%1 = OpVariable %2 Output %4
 )");
 }
 
@@ -192,7 +210,8 @@ OpDecorate %1 DescriptorSet 3
 )");
   EXPECT_EQ(DumpInstructions(b.types()), R"(%3 = OpTypeFloat 32
 %2 = OpTypePointer Output %3
-%1 = OpVariable %2 Output
+%4 = OpConstantNull %3
+%1 = OpVariable %2 Output %4
 )");
 }
 
@@ -216,7 +235,8 @@ TEST_F(BuilderTest, GlobalVar_WithBuiltin) {
 )");
   EXPECT_EQ(DumpInstructions(b.types()), R"(%3 = OpTypeFloat 32
 %2 = OpTypePointer Output %3
-%1 = OpVariable %2 Output
+%4 = OpConstantNull %3
+%1 = OpVariable %2 Output %4
 )");
 }
 
diff --git a/src/writer/spirv/builder_ident_expression_test.cc b/src/writer/spirv/builder_ident_expression_test.cc
index 5fb39b59d7..c48133092a 100644
--- a/src/writer/spirv/builder_ident_expression_test.cc
+++ b/src/writer/spirv/builder_ident_expression_test.cc
@@ -96,7 +96,8 @@ TEST_F(BuilderTest, IdentifierExpression_GlobalVar) {
 )");
   EXPECT_EQ(DumpInstructions(b.types()), R"(%3 = OpTypeFloat 32
 %2 = OpTypePointer Output %3
-%1 = OpVariable %2 Output
+%4 = OpConstantNull %3
+%1 = OpVariable %2 Output %4
 )");
 
   ast::IdentifierExpression expr("var");
@@ -161,10 +162,12 @@ TEST_F(BuilderTest, IdentifierExpression_FunctionVar) {
 )");
   EXPECT_EQ(DumpInstructions(b.types()), R"(%3 = OpTypeFloat 32
 %2 = OpTypePointer Function %3
+%4 = OpConstantNull %3
 )");
 
   const auto& func = b.functions()[0];
-  EXPECT_EQ(DumpInstructions(func.variables()), R"(%1 = OpVariable %2 Function
+  EXPECT_EQ(DumpInstructions(func.variables()),
+            R"(%1 = OpVariable %2 Function %4
 )");
 
   ast::IdentifierExpression expr("var");
@@ -195,15 +198,16 @@ TEST_F(BuilderTest, IdentifierExpression_Load) {
   b.push_function(Function{});
   ASSERT_TRUE(b.GenerateGlobalVariable(&var)) << b.error();
 
-  EXPECT_EQ(b.GenerateBinaryExpression(&expr), 6u) << b.error();
+  EXPECT_EQ(b.GenerateBinaryExpression(&expr), 7u) << b.error();
   EXPECT_EQ(DumpInstructions(b.types()), R"(%3 = OpTypeInt 32 1
 %2 = OpTypePointer Private %3
-%1 = OpVariable %2 Private
+%4 = OpConstantNull %3
+%1 = OpVariable %2 Private %4
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
-            R"(%4 = OpLoad %3 %1
-%5 = OpLoad %3 %1
-%6 = OpIAdd %3 %4 %5
+            R"(%5 = OpLoad %3 %1
+%6 = OpLoad %3 %1
+%7 = OpIAdd %3 %5 %6
 )");
 }
 
diff --git a/src/writer/spirv/builder_if_test.cc b/src/writer/spirv/builder_if_test.cc
index dbe1dc4e4c..b41d1e05ed 100644
--- a/src/writer/spirv/builder_if_test.cc
+++ b/src/writer/spirv/builder_if_test.cc
@@ -107,18 +107,19 @@ TEST_F(BuilderTest, If_WithStatements) {
   EXPECT_TRUE(b.GenerateIfStatement(&expr)) << b.error();
   EXPECT_EQ(DumpInstructions(b.types()), R"(%3 = OpTypeInt 32 1
 %2 = OpTypePointer Private %3
-%1 = OpVariable %2 Private
-%4 = OpTypeBool
-%5 = OpConstantTrue %4
-%8 = OpConstant %3 2
+%4 = OpConstantNull %3
+%1 = OpVariable %2 Private %4
+%5 = OpTypeBool
+%6 = OpConstantTrue %5
+%9 = OpConstant %3 2
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
-            R"(OpSelectionMerge %6 None
-OpBranchConditional %5 %7 %6
+            R"(OpSelectionMerge %7 None
+OpBranchConditional %6 %8 %7
+%8 = OpLabel
+OpStore %1 %9
+OpBranch %7
 %7 = OpLabel
-OpStore %1 %8
-OpBranch %6
-%6 = OpLabel
 )");
 }
 
@@ -170,22 +171,23 @@ TEST_F(BuilderTest, If_WithElse) {
   EXPECT_TRUE(b.GenerateIfStatement(&expr)) << b.error();
   EXPECT_EQ(DumpInstructions(b.types()), R"(%3 = OpTypeInt 32 1
 %2 = OpTypePointer Private %3
-%1 = OpVariable %2 Private
-%4 = OpTypeBool
-%5 = OpConstantTrue %4
-%9 = OpConstant %3 2
-%10 = OpConstant %3 3
+%4 = OpConstantNull %3
+%1 = OpVariable %2 Private %4
+%5 = OpTypeBool
+%6 = OpConstantTrue %5
+%10 = OpConstant %3 2
+%11 = OpConstant %3 3
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
-            R"(OpSelectionMerge %6 None
-OpBranchConditional %5 %7 %8
-%7 = OpLabel
-OpStore %1 %9
-OpBranch %6
+            R"(OpSelectionMerge %7 None
+OpBranchConditional %6 %8 %9
 %8 = OpLabel
 OpStore %1 %10
-OpBranch %6
-%6 = OpLabel
+OpBranch %7
+%9 = OpLabel
+OpStore %1 %11
+OpBranch %7
+%7 = OpLabel
 )");
 }
 
@@ -240,27 +242,28 @@ TEST_F(BuilderTest, If_WithElseIf) {
   EXPECT_TRUE(b.GenerateIfStatement(&expr)) << b.error();
   EXPECT_EQ(DumpInstructions(b.types()), R"(%3 = OpTypeInt 32 1
 %2 = OpTypePointer Private %3
-%1 = OpVariable %2 Private
-%4 = OpTypeBool
-%5 = OpConstantTrue %4
-%9 = OpConstant %3 2
-%12 = OpConstant %3 3
+%4 = OpConstantNull %3
+%1 = OpVariable %2 Private %4
+%5 = OpTypeBool
+%6 = OpConstantTrue %5
+%10 = OpConstant %3 2
+%13 = OpConstant %3 3
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
-            R"(OpSelectionMerge %6 None
-OpBranchConditional %5 %7 %8
-%7 = OpLabel
-OpStore %1 %9
-OpBranch %6
+            R"(OpSelectionMerge %7 None
+OpBranchConditional %6 %8 %9
 %8 = OpLabel
-OpSelectionMerge %10 None
-OpBranchConditional %5 %11 %10
+OpStore %1 %10
+OpBranch %7
+%9 = OpLabel
+OpSelectionMerge %11 None
+OpBranchConditional %6 %12 %11
+%12 = OpLabel
+OpStore %1 %13
+OpBranch %11
 %11 = OpLabel
-OpStore %1 %12
-OpBranch %10
-%10 = OpLabel
-OpBranch %6
-%6 = OpLabel
+OpBranch %7
+%7 = OpLabel
 )");
 }
 
@@ -334,41 +337,42 @@ TEST_F(BuilderTest, If_WithMultiple) {
   EXPECT_TRUE(b.GenerateIfStatement(&expr)) << b.error();
   EXPECT_EQ(DumpInstructions(b.types()), R"(%3 = OpTypeInt 32 1
 %2 = OpTypePointer Private %3
-%1 = OpVariable %2 Private
-%4 = OpTypeBool
-%5 = OpConstantTrue %4
-%9 = OpConstant %3 2
-%13 = OpConstant %3 3
-%14 = OpConstantFalse %4
-%18 = OpConstant %3 4
-%19 = OpConstant %3 5
+%4 = OpConstantNull %3
+%1 = OpVariable %2 Private %4
+%5 = OpTypeBool
+%6 = OpConstantTrue %5
+%10 = OpConstant %3 2
+%14 = OpConstant %3 3
+%15 = OpConstantFalse %5
+%19 = OpConstant %3 4
+%20 = OpConstant %3 5
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
-            R"(OpSelectionMerge %6 None
-OpBranchConditional %5 %7 %8
-%7 = OpLabel
-OpStore %1 %9
-OpBranch %6
+            R"(OpSelectionMerge %7 None
+OpBranchConditional %6 %8 %9
 %8 = OpLabel
-OpSelectionMerge %10 None
-OpBranchConditional %5 %11 %12
-%11 = OpLabel
-OpStore %1 %13
-OpBranch %10
+OpStore %1 %10
+OpBranch %7
+%9 = OpLabel
+OpSelectionMerge %11 None
+OpBranchConditional %6 %12 %13
 %12 = OpLabel
-OpSelectionMerge %15 None
-OpBranchConditional %14 %16 %17
-%16 = OpLabel
-OpStore %1 %18
-OpBranch %15
+OpStore %1 %14
+OpBranch %11
+%13 = OpLabel
+OpSelectionMerge %16 None
+OpBranchConditional %15 %17 %18
 %17 = OpLabel
 OpStore %1 %19
-OpBranch %15
-%15 = OpLabel
-OpBranch %10
-%10 = OpLabel
-OpBranch %6
-%6 = OpLabel
+OpBranch %16
+%18 = OpLabel
+OpStore %1 %20
+OpBranch %16
+%16 = OpLabel
+OpBranch %11
+%11 = OpLabel
+OpBranch %7
+%7 = OpLabel
 )");
 }
 
diff --git a/src/writer/spirv/builder_loop_test.cc b/src/writer/spirv/builder_loop_test.cc
index 6333fad522..0b59ac3da3 100644
--- a/src/writer/spirv/builder_loop_test.cc
+++ b/src/writer/spirv/builder_loop_test.cc
@@ -94,20 +94,21 @@ TEST_F(BuilderTest, Loop_WithoutContinuing) {
   EXPECT_TRUE(b.GenerateLoopStatement(&expr)) << b.error();
   EXPECT_EQ(DumpInstructions(b.types()), R"(%3 = OpTypeInt 32 1
 %2 = OpTypePointer Private %3
-%1 = OpVariable %2 Private
-%8 = OpConstant %3 2
+%4 = OpConstantNull %3
+%1 = OpVariable %2 Private %4
+%9 = OpConstant %3 2
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
-            R"(OpBranch %4
-%4 = OpLabel
-OpLoopMerge %5 %6 None
+            R"(OpBranch %5
+%5 = OpLabel
+OpLoopMerge %6 %7 None
+OpBranch %8
+%8 = OpLabel
+OpStore %1 %9
 OpBranch %7
 %7 = OpLabel
-OpStore %1 %8
-OpBranch %6
+OpBranch %5
 %6 = OpLabel
-OpBranch %4
-%5 = OpLabel
 )");
 }
 
@@ -149,22 +150,23 @@ TEST_F(BuilderTest, Loop_WithContinuing) {
   EXPECT_TRUE(b.GenerateLoopStatement(&expr)) << b.error();
   EXPECT_EQ(DumpInstructions(b.types()), R"(%3 = OpTypeInt 32 1
 %2 = OpTypePointer Private %3
-%1 = OpVariable %2 Private
-%8 = OpConstant %3 2
-%9 = OpConstant %3 3
+%4 = OpConstantNull %3
+%1 = OpVariable %2 Private %4
+%9 = OpConstant %3 2
+%10 = OpConstant %3 3
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
-            R"(OpBranch %4
-%4 = OpLabel
-OpLoopMerge %5 %6 None
+            R"(OpBranch %5
+%5 = OpLabel
+OpLoopMerge %6 %7 None
+OpBranch %8
+%8 = OpLabel
+OpStore %1 %9
 OpBranch %7
 %7 = OpLabel
-OpStore %1 %8
-OpBranch %6
+OpStore %1 %10
+OpBranch %5
 %6 = OpLabel
-OpStore %1 %9
-OpBranch %4
-%5 = OpLabel
 )");
 }