[spirv-writer] Add start of cast support.

This CL starts support for the cast expression. It adds the i32 to f32
conversion path.

Bug: tint:5
Change-Id: Id1eafc38592060c4b5b91964302d79a847e2edaf
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/20628
Reviewed-by: David Neto <dneto@google.com>

BUILD.gn

@@ -686,6 +686,7 @@ source_set("tint_unittests_spv_writer_src") {
     "src/writer/spirv/builder_assign_test.cc",
     "src/writer/spirv/builder_binary_expression_test.cc",
     "src/writer/spirv/builder_call_test.cc",
+    "src/writer/spirv/builder_cast_expression_test.cc",
     "src/writer/spirv/builder_constructor_expression_test.cc",
     "src/writer/spirv/builder_entry_point_test.cc",
     "src/writer/spirv/builder_function_test.cc",

src/CMakeLists.txt

@@ -431,6 +431,7 @@ if(${TINT_BUILD_SPV_WRITER})
     writer/spirv/builder_assign_test.cc
     writer/spirv/builder_binary_expression_test.cc
     writer/spirv/builder_call_test.cc
+    writer/spirv/builder_cast_expression_test.cc
     writer/spirv/builder_constructor_expression_test.cc
     writer/spirv/builder_entry_point_test.cc
     writer/spirv/builder_function_test.cc

src/type_determiner.cc

@@ -359,6 +359,10 @@ bool TypeDeterminer::DetermineCall(ast::CallExpression* expr) {
 }
 
 bool TypeDeterminer::DetermineCast(ast::CastExpression* expr) {
+  if (!DetermineResultType(expr->expr())) {
+    return false;
+  }
+
   expr->set_result_type(expr->type());
   return true;
 }

src/writer/spirv/builder.cc

@@ -25,6 +25,7 @@
 #include "src/ast/bool_literal.h"
 #include "src/ast/builtin_decoration.h"
 #include "src/ast/call_expression.h"
+#include "src/ast/cast_expression.h"
 #include "src/ast/constructor_expression.h"
 #include "src/ast/decorated_variable.h"
 #include "src/ast/else_statement.h"
@@ -297,6 +298,9 @@ uint32_t Builder::GenerateExpression(ast::Expression* expr) {
   if (expr->IsCall()) {
     return GenerateCallExpression(expr->AsCall());
   }
+  if (expr->IsCast()) {
+    return GenerateCastExpression(expr->AsCast());
+  }
   if (expr->IsConstructor()) {
     return GenerateConstructorExpression(expr->AsConstructor(), false);
   }
@@ -1145,6 +1149,44 @@ uint32_t Builder::GenerateCallExpression(ast::CallExpression* expr) {
   return result_id;
 }
 
+uint32_t Builder::GenerateCastExpression(ast::CastExpression* cast) {
+  auto result = result_op();
+  auto result_id = result.to_i();
+
+  auto result_type_id = GenerateTypeIfNeeded(cast->result_type());
+  if (result_type_id == 0) {
+    return 0;
+  }
+
+  auto val_id = GenerateExpression(cast->expr());
+  if (val_id == 0) {
+    return 0;
+  }
+
+  auto* to_type = cast->result_type()->UnwrapPtrIfNeeded();
+  auto* from_type = cast->expr()->result_type()->UnwrapPtrIfNeeded();
+
+  spv::Op op = spv::Op::OpNop;
+  if (from_type->IsI32() && to_type->IsF32()) {
+    op = spv::Op::OpConvertSToF;
+  } else if (from_type->IsU32() && to_type->IsF32()) {
+    op = spv::Op::OpConvertUToF;
+  } else if (from_type->IsF32() && to_type->IsI32()) {
+    op = spv::Op::OpConvertFToS;
+  } else if (from_type->IsF32() && to_type->IsU32()) {
+    op = spv::Op::OpConvertFToU;
+  }
+  if (op == spv::Op::OpNop) {
+    error_ = "unable to determine conversion type for cast";
+    return 0;
+  }
+
+  push_function_inst(
+      op, {Operand::Int(result_type_id), result, Operand::Int(val_id)});
+
+  return result_id;
+}
+
 bool Builder::GenerateConditionalBlock(
     ast::Expression* cond,
     const ast::StatementList& true_body,

src/writer/spirv/builder.h

@@ -279,6 +279,10 @@ class Builder {
   /// @param expr the expression to generate
   /// @returns the expression ID on success or 0 otherwise
   uint32_t GenerateCallExpression(ast::CallExpression* expr);
+  /// Generates a cast expression
+  /// @param expr the expression to generate
+  /// @returns the expression ID on success or 0 otherwise
+  uint32_t GenerateCastExpression(ast::CastExpression* expr);
   /// Generates a loop statement
   /// @param stmt the statement to generate
   /// @returns true on successful generation

src/writer/spirv/builder_cast_expression_test.cc

@@ -0,0 +1,76 @@
+// 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 "gtest/gtest.h"
+#include "src/ast/cast_expression.h"
+#include "src/ast/float_literal.h"
+#include "src/ast/int_literal.h"
+#include "src/ast/module.h"
+#include "src/ast/scalar_constructor_expression.h"
+#include "src/ast/type/f32_type.h"
+#include "src/ast/type/i32_type.h"
+#include "src/context.h"
+#include "src/type_determiner.h"
+#include "src/writer/spirv/builder.h"
+#include "src/writer/spirv/spv_dump.h"
+
+namespace tint {
+namespace writer {
+namespace spirv {
+namespace {
+
+using BuilderTest = testing::Test;
+
+TEST_F(BuilderTest, DISABLED_Cast_FloatToU32) {}
+
+TEST_F(BuilderTest, DISABLED_Cast_FloatToI32) {}
+
+TEST_F(BuilderTest, Cast_I32ToFloat) {
+  ast::type::I32Type i32;
+  ast::type::F32Type f32;
+
+  ast::CastExpression cast(&f32,
+                           std::make_unique<ast::ScalarConstructorExpression>(
+                               std::make_unique<ast::IntLiteral>(&i32, 2)));
+
+  Context ctx;
+  ast::Module mod;
+  TypeDeterminer td(&ctx, &mod);
+  ASSERT_TRUE(td.DetermineResultType(&cast)) << td.error();
+
+  Builder b(&mod);
+  b.push_function(Function{});
+  EXPECT_EQ(b.GenerateCastExpression(&cast), 1u);
+
+  EXPECT_EQ(DumpInstructions(b.types()), R"(%2 = OpTypeFloat 32
+%3 = OpTypeInt 32 1
+%4 = OpConstant %3 2
+)");
+  EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
+            R"(%1 = OpConvertSToF %2 %4
+)");
+}
+
+TEST_F(BuilderTest, DISABLED_Cast_U32ToFloat) {}
+
+TEST_F(BuilderTest, DISABLED_Cast_WithLoad) {}
+
+TEST_F(BuilderTest, DISABLED_Cast_WithAlias) {}
+
+// TODO(dsinclair): Are here i32 -> u32 and u32->i32 casts?
+
+}  // namespace
+}  // namespace spirv
+}  // namespace writer
+}  // namespace tint