writer/spirv: Support overridable workgroup sizes

Generate an OpSpecConstantComposite instruction decorated with the
WorkgroupSize builtin. Only support a single stage with an overridable
workgroup size.

Bug: tint:713
Change-Id: I139123c0af8326fcbd796cb2fc9d223882206e19
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/51263
Commit-Queue: James Price <jrprice@google.com>
Auto-Submit: James Price <jrprice@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>

src/writer/spirv/builder.cc

@@ -444,12 +444,55 @@ bool Builder::GenerateExecutionModes(ast::Function* func, uint32_t id) {
         {Operand::Int(id), Operand::Int(SpvExecutionModeOriginUpperLeft)});
   } else if (func->pipeline_stage() == ast::PipelineStage::kCompute) {
     auto& wgsize = func_sem->workgroup_size();
+
+    // Check if the workgroup_size uses pipeline-overridable constants.
     if (wgsize[0].overridable_const || wgsize[1].overridable_const ||
         wgsize[2].overridable_const) {
-      // TODO(crbug.com/tint/713): Handle overridable constants.
-      TINT_UNIMPLEMENTED(builder_.Diagnostics())
-          << "pipeline-overridable workgroup sizes are not implemented";
+      if (has_overridable_workgroup_size_) {
+        // Only one stage can have a pipeline-overridable workgroup size.
+        // TODO(crbug.com/tint/810): Use LocalSizeId to handle this scenario.
+        TINT_ICE(builder_.Diagnostics())
+            << "multiple stages using pipeline-overridable workgroup sizes";
       }
+      has_overridable_workgroup_size_ = true;
+
+      sem::U32 u32;
+      sem::Vector vec3_u32(&u32, 3);
+      uint32_t vec3_u32_type_id = GenerateTypeIfNeeded(&vec3_u32);
+      if (vec3_u32_type_id == 0) {
+        return 0;
+      }
+
+      OperandList wgsize_ops;
+      auto wgsize_result = result_op();
+      wgsize_ops.push_back(Operand::Int(vec3_u32_type_id));
+      wgsize_ops.push_back(wgsize_result);
+
+      // Generate OpConstant instructions for each dimension.
+      for (int i = 0; i < 3; i++) {
+        auto constant = ScalarConstant::U32(wgsize[i].value);
+        if (wgsize[i].overridable_const) {
+          // Make the constant specializable.
+          auto* sem_const = builder_.Sem().Get(wgsize[i].overridable_const);
+          if (!sem_const->IsPipelineConstant()) {
+            TINT_ICE(builder_.Diagnostics())
+                << "expected a pipeline-overridable constant";
+          }
+          constant.is_spec_op = true;
+          constant.constant_id = sem_const->ConstantId();
+        }
+
+        auto result = GenerateConstantIfNeeded(constant);
+        wgsize_ops.push_back(Operand::Int(result));
+      }
+
+      // Generate the WorkgroupSize builtin.
+      push_type(spv::Op::OpSpecConstantComposite, wgsize_ops);
+      push_annot(spv::Op::OpDecorate,
+                 {wgsize_result, Operand::Int(SpvDecorationBuiltIn),
+                  Operand::Int(SpvBuiltInWorkgroupSize)});
+    } else {
+      // Not overridable, so just use OpExecutionMode LocalSize.
       uint32_t x = wgsize[0].value;
       uint32_t y = wgsize[1].value;
       uint32_t z = wgsize[2].value;
@@ -458,6 +501,7 @@ bool Builder::GenerateExecutionModes(ast::Function* func, uint32_t id) {
           {Operand::Int(id), Operand::Int(SpvExecutionModeLocalSize),
            Operand::Int(x), Operand::Int(y), Operand::Int(z)});
     }
+  }
 
   for (auto builtin : func_sem->ReferencedBuiltinVariables()) {
     if (builtin.second->value() == ast::Builtin::kFragDepth) {

src/writer/spirv/builder.h

@@ -533,6 +533,7 @@ class Builder {
   std::vector<uint32_t> merge_stack_;
   std::vector<uint32_t> continue_stack_;
   std::unordered_set<uint32_t> capability_set_;
+  bool has_overridable_workgroup_size_ = false;
 };
 
 }  // namespace spirv

src/writer/spirv/builder_function_decoration_test.cc

@@ -197,7 +197,7 @@ TEST_F(BuilderTest, Decoration_ExecutionMode_WorkgroupSize_Default) {
 )");
 }
 
-TEST_F(BuilderTest, Decoration_ExecutionMode_WorkgroupSize) {
+TEST_F(BuilderTest, Decoration_ExecutionMode_WorkgroupSize_Literals) {
   auto* func = Func("main", {}, ty.void_(), ast::StatementList{},
                     ast::DecorationList{
                         WorkgroupSize(2, 4, 6),
@@ -212,6 +212,81 @@ TEST_F(BuilderTest, Decoration_ExecutionMode_WorkgroupSize) {
 )");
 }
 
+TEST_F(BuilderTest, Decoration_ExecutionMode_WorkgroupSize_Const) {
+  GlobalConst("width", ty.i32(), Construct(ty.i32(), 2));
+  GlobalConst("height", ty.i32(), Construct(ty.i32(), 3));
+  GlobalConst("depth", ty.i32(), Construct(ty.i32(), 4));
+  auto* func = Func("main", {}, ty.void_(), ast::StatementList{},
+                    ast::DecorationList{
+                        WorkgroupSize("width", "height", "depth"),
+                        Stage(ast::PipelineStage::kCompute),
+                    });
+
+  spirv::Builder& b = Build();
+
+  ASSERT_TRUE(b.GenerateExecutionModes(func, 3)) << b.error();
+  EXPECT_EQ(DumpInstructions(b.execution_modes()),
+            R"(OpExecutionMode %3 LocalSize 2 3 4
+)");
+}
+
+TEST_F(BuilderTest, Decoration_ExecutionMode_WorkgroupSize_OverridableConst) {
+  GlobalConst("width", ty.i32(), Construct(ty.i32(), 2), {Override(7u)});
+  GlobalConst("height", ty.i32(), Construct(ty.i32(), 3), {Override(8u)});
+  GlobalConst("depth", ty.i32(), Construct(ty.i32(), 4), {Override(9u)});
+  auto* func = Func("main", {}, ty.void_(), ast::StatementList{},
+                    ast::DecorationList{
+                        WorkgroupSize("width", "height", "depth"),
+                        Stage(ast::PipelineStage::kCompute),
+                    });
+
+  spirv::Builder& b = Build();
+
+  ASSERT_TRUE(b.GenerateExecutionModes(func, 3)) << b.error();
+  EXPECT_EQ(DumpInstructions(b.execution_modes()), "");
+  EXPECT_EQ(DumpInstructions(b.types()),
+            R"(%2 = OpTypeInt 32 0
+%1 = OpTypeVector %2 3
+%4 = OpSpecConstant %2 2
+%5 = OpSpecConstant %2 3
+%6 = OpSpecConstant %2 4
+%3 = OpSpecConstantComposite %1 %4 %5 %6
+)");
+  EXPECT_EQ(DumpInstructions(b.annots()),
+            R"(OpDecorate %4 SpecId 7
+OpDecorate %5 SpecId 8
+OpDecorate %6 SpecId 9
+OpDecorate %3 BuiltIn WorkgroupSize
+)");
+}
+
+TEST_F(BuilderTest, Decoration_ExecutionMode_WorkgroupSize_LiteralAndConst) {
+  GlobalConst("height", ty.i32(), Construct(ty.i32(), 2), {Override(7u)});
+  GlobalConst("depth", ty.i32(), Construct(ty.i32(), 3));
+  auto* func = Func("main", {}, ty.void_(), ast::StatementList{},
+                    ast::DecorationList{
+                        WorkgroupSize(4, "height", "depth"),
+                        Stage(ast::PipelineStage::kCompute),
+                    });
+
+  spirv::Builder& b = Build();
+
+  ASSERT_TRUE(b.GenerateExecutionModes(func, 3)) << b.error();
+  EXPECT_EQ(DumpInstructions(b.execution_modes()), "");
+  EXPECT_EQ(DumpInstructions(b.types()),
+            R"(%2 = OpTypeInt 32 0
+%1 = OpTypeVector %2 3
+%4 = OpConstant %2 4
+%5 = OpSpecConstant %2 2
+%6 = OpConstant %2 3
+%3 = OpSpecConstantComposite %1 %4 %5 %6
+)");
+  EXPECT_EQ(DumpInstructions(b.annots()),
+            R"(OpDecorate %5 SpecId 7
+OpDecorate %3 BuiltIn WorkgroupSize
+)");
+}
+
 TEST_F(BuilderTest, Decoration_ExecutionMode_MultipleFragment) {
   auto* func1 = Func("main1", {}, ty.void_(), ast::StatementList{},
                      ast::DecorationList{