writer/spirv: Fix static array accessors

If the array accessor expression uses a literal index, generate an
OpCompositeExtract instruction. Dynamic indices will be handled in a
follow-up patch.

Fixed: tint:767
Change-Id: I79a980d7d558a49def30816d04dcaa566f284c8f
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/49701
Reviewed-by: David Neto <dneto@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: James Price <jrprice@google.com>
Auto-Submit: James Price <jrprice@google.com>

src/writer/spirv/builder.cc

@@ -839,14 +839,22 @@ bool Builder::GenerateArrayAccessor(ast::ArrayAccessorExpression* expr,
     return false;
   }
 
-  // We don't have a pointer, so we have to extract value from the vector
+  // We don't have a pointer, so we can just directly extract the value.
   auto extract = result_op();
   auto extract_id = extract.to_i();
 
-  if (!push_function_inst(
-          spv::Op::OpVectorExtractDynamic,
-          {Operand::Int(result_type_id), extract, Operand::Int(info->source_id),
-           Operand::Int(idx_id)})) {
+  // If the index is a literal, we use OpCompositeExtract.
+  if (auto* scalar = expr->idx_expr()->As<ast::ScalarConstructorExpression>()) {
+    auto* literal = scalar->literal()->As<ast::IntLiteral>();
+    if (!literal) {
+      TINT_ICE(builder_.Diagnostics()) << "bad literal in array accessor";
+      return false;
+    }
+
+    if (!push_function_inst(spv::Op::OpCompositeExtract,
+                            {Operand::Int(result_type_id), extract,
+                             Operand::Int(info->source_id),
+                             Operand::Int(literal->value_as_u32())})) {
       return false;
     }
 
@@ -854,6 +862,25 @@ bool Builder::GenerateArrayAccessor(ast::ArrayAccessorExpression* expr,
     info->source_type = TypeOf(expr);
 
     return true;
+  }
+
+  // If the source is a vector, we use OpVectorExtractDynamic.
+  if (info->source_type->Is<sem::Vector>()) {
+    if (!push_function_inst(
+            spv::Op::OpVectorExtractDynamic,
+            {Operand::Int(result_type_id), extract,
+             Operand::Int(info->source_id), Operand::Int(idx_id)})) {
+      return false;
+    }
+
+    info->source_id = extract_id;
+    info->source_type = TypeOf(expr);
+
+    return true;
+  }
+
+  TINT_ICE(builder_.Diagnostics()) << "unsupported array accessor expression";
+  return false;
 }
 
 bool Builder::GenerateMemberAccessor(ast::MemberAccessorExpression* expr,

src/writer/spirv/builder_accessor_expression_test.cc

@@ -676,7 +676,7 @@ TEST_F(BuilderTest, MemberAccessor_Array_of_Swizzle) {
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
             R"(%6 = OpLoad %3 %1
 %7 = OpVectorShuffle %3 %6 %6 1 0 2
-%10 = OpVectorExtractDynamic %4 %7 %9
+%10 = OpCompositeExtract %4 %7 1
 )");
 }
 
@@ -806,7 +806,7 @@ TEST_F(BuilderTest, Accessor_Const_Vec) {
   spirv::Builder& b = Build();
 
   b.push_function(Function{});
-  ASSERT_TRUE(b.GenerateFunctionVariable(var)) << b.error();
+  ASSERT_TRUE(b.GenerateGlobalVariable(var)) << b.error();
   EXPECT_EQ(b.GenerateAccessorExpression(expr), 8u) << b.error();
 
   EXPECT_EQ(DumpInstructions(b.types()), R"(%2 = OpTypeFloat 32
@@ -819,16 +819,89 @@ TEST_F(BuilderTest, Accessor_Const_Vec) {
 )");
   EXPECT_EQ(DumpInstructions(b.functions()[0].variables()), "");
   EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
-            R"(%8 = OpVectorExtractDynamic %2 %5 %7
+            R"(%8 = OpCompositeExtract %2 %5 1
 )");
 }
 
-TEST_F(BuilderTest, DISABLED_Accessor_Array_NonPointer) {
+TEST_F(BuilderTest, Accessor_Const_Vec_Dynamic) {
+  // let pos : vec2<f32> = vec2<f32>(0.0, 0.5);
+  // idx : i32
+  // pos[idx]
+
+  auto* var = GlobalConst("pos", ty.vec2<f32>(), vec2<f32>(0.0f, 0.5f));
+
+  auto* idx = Var("idx", ty.i32(), ast::StorageClass::kFunction);
+  auto* expr = IndexAccessor("pos", idx);
+
+  ast::StatementList body;
+  body.push_back(WrapInStatement(idx));
+  body.push_back(WrapInStatement(expr));
+  WrapInFunction(body);
+
+  spirv::Builder& b = Build();
+
+  b.push_function(Function{});
+  ASSERT_TRUE(b.GenerateGlobalVariable(var)) << b.error();
+  ASSERT_TRUE(b.GenerateFunctionVariable(idx)) << b.error();
+  EXPECT_EQ(b.GenerateAccessorExpression(expr), 11u) << b.error();
+
+  EXPECT_EQ(DumpInstructions(b.types()), R"(%2 = OpTypeFloat 32
+%1 = OpTypeVector %2 2
+%3 = OpConstant %2 0
+%4 = OpConstant %2 0.5
+%5 = OpConstantComposite %1 %3 %4
+%8 = OpTypeInt 32 1
+%7 = OpTypePointer Function %8
+%9 = OpConstantNull %8
+)");
+  EXPECT_EQ(DumpInstructions(b.functions()[0].variables()),
+            R"(%6 = OpVariable %7 Function %9
+)");
+  EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
+            R"(%10 = OpLoad %8 %6
+%11 = OpVectorExtractDynamic %2 %5 %10
+)");
+}
+
+TEST_F(BuilderTest, Accessor_Array_NonPointer) {
   // let a : array<f32, 3>;
   // a[2]
+
+  auto* var = GlobalConst("a", ty.array<f32, 3>(),
+                          Construct(ty.array<f32, 3>(), 0.0f, 0.5f, 1.0f));
+  auto* expr = IndexAccessor("a", 2);
+  WrapInFunction(expr);
+
+  spirv::Builder& b = Build();
+
+  b.push_function(Function{});
+  ASSERT_TRUE(b.GenerateGlobalVariable(var)) << b.error();
+  EXPECT_EQ(b.GenerateAccessorExpression(expr), 11u) << b.error();
+
+  EXPECT_EQ(DumpInstructions(b.types()), R"(%2 = OpTypeFloat 32
+%3 = OpTypeInt 32 0
+%4 = OpConstant %3 3
+%1 = OpTypeArray %2 %4
+%5 = OpConstant %2 0
+%6 = OpConstant %2 0.5
+%7 = OpConstant %2 1
+%8 = OpConstantComposite %1 %5 %6 %7
+%9 = OpTypeInt 32 1
+%10 = OpConstant %9 2
+)");
+  EXPECT_EQ(DumpInstructions(b.functions()[0].variables()), "");
+  EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
+            R"(%11 = OpCompositeExtract %2 %8 2
+)");
+}
+
+TEST_F(BuilderTest, DISABLED_Accessor_Array_NonPointer_Dynamic) {
+  // let a : array<f32, 3>;
+  // idx : i32
+  // a[idx]
   //
-  // This has to generate an OpConstantExtract and will need to read the 3 value
-  // out of the ScalarConstructor as extract requires integer indices.
+  // This needs to copy the array to an OpVariable in the Function storage class
+  // and then access chain into it and load the result.
 }
 
 }  // namespace