[validator] Remove requirement to have an entry point

The SPIR-V and HLSL sanitizing transforms add an empty one if
necessary.

Fixed: tint:679
Change-Id: Ic98ff3109d7381b1fbc2de68d95d57e15c7a67c0
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/46700
Commit-Queue: Ben Clayton <bclayton@google.com>
Auto-Submit: James Price <jrprice@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>

src/transform/hlsl.cc

@@ -16,6 +16,7 @@
 
 #include <utility>
 
+#include "src/ast/stage_decoration.h"
 #include "src/ast/variable_decl_statement.h"
 #include "src/program_builder.h"
 #include "src/semantic/expression.h"
@@ -32,6 +33,7 @@ Transform::Output Hlsl::Run(const Program* in, const DataMap&) {
   ProgramBuilder out;
   CloneContext ctx(&out, in);
   PromoteArrayInitializerToConstVar(ctx);
+  AddEmptyEntryPoint(ctx);
   ctx.Clone();
   return Output{Program(std::move(out))};
 }
@@ -105,5 +107,16 @@ void Hlsl::PromoteArrayInitializerToConstVar(CloneContext& ctx) const {
   }
 }
 
+void Hlsl::AddEmptyEntryPoint(CloneContext& ctx) const {
+  for (auto* func : ctx.src->AST().Functions()) {
+    if (func->IsEntryPoint()) {
+      return;
+    }
+  }
+  ctx.dst->Func(
+      "_tint_unused_entry_point", {}, ctx.dst->ty.void_(), {},
+      {ctx.dst->create<ast::StageDecoration>(ast::PipelineStage::kVertex)});
+}
+
 }  // namespace transform
 }  // namespace tint

src/transform/hlsl.h

@@ -44,6 +44,8 @@ class Hlsl : public Transform {
   /// the array usage statement.
   /// See crbug.com/tint/406 for more details
   void PromoteArrayInitializerToConstVar(CloneContext& ctx) const;
+  /// Add an empty shader entry point if none exist in the module.
+  void AddEmptyEntryPoint(CloneContext& ctx) const;
 };
 
 }  // namespace transform

src/transform/hlsl_test.cc

@@ -143,6 +143,20 @@ fn main() -> void {
   EXPECT_EQ(expect, str(got));
 }
 
+TEST_F(HlslTest, AddEmptyEntryPoint) {
+  auto* src = R"()";
+
+  auto* expect = R"(
+[[stage(vertex)]]
+fn _tint_unused_entry_point() -> void {
+}
+)";
+
+  auto got = Run<Hlsl>(src);
+
+  EXPECT_EQ(expect, str(got));
+}
+
 }  // namespace
 }  // namespace transform
 }  // namespace tint

src/transform/spirv.cc

@@ -19,6 +19,7 @@
 
 #include "src/ast/call_statement.h"
 #include "src/ast/return_statement.h"
+#include "src/ast/stage_decoration.h"
 #include "src/program_builder.h"
 #include "src/semantic/function.h"
 #include "src/semantic/statement.h"
@@ -42,6 +43,7 @@ Transform::Output Spirv::Run(const Program* in, const DataMap&) {
   ProgramBuilder out2;
   CloneContext ctx2(&out2, &tmp);
   HandleSampleMaskBuiltins(ctx2);
+  AddEmptyEntryPoint(ctx2);
   ctx2.Clone();
 
   return Output{Program(std::move(out2))};
@@ -234,6 +236,17 @@ void Spirv::HandleSampleMaskBuiltins(CloneContext& ctx) const {
   }
 }
 
+void Spirv::AddEmptyEntryPoint(CloneContext& ctx) const {
+  for (auto* func : ctx.src->AST().Functions()) {
+    if (func->IsEntryPoint()) {
+      return;
+    }
+  }
+  ctx.dst->Func(
+      "_tint_unused_entry_point", {}, ctx.dst->ty.void_(), {},
+      {ctx.dst->create<ast::StageDecoration>(ast::PipelineStage::kCompute)});
+}
+
 Symbol Spirv::HoistToInputVariables(
     CloneContext& ctx,
     const ast::Function* func,

src/transform/spirv.h

@@ -47,6 +47,8 @@ class Spirv : public Transform {
   void HandleEntryPointIOTypes(CloneContext& ctx) const;
   /// Change type of sample mask builtin variables to single element arrays.
   void HandleSampleMaskBuiltins(CloneContext& ctx) const;
+  /// Add an empty shader entry point if none exist in the module.
+  void AddEmptyEntryPoint(CloneContext& ctx) const;
 
   /// Recursively create module-scope input variables for `ty` and add
   /// function-scope variables for structs to `func`.

src/transform/spirv_test.cc

@@ -833,6 +833,20 @@ fn main() -> void {
   EXPECT_EQ(expect, str(got));
 }
 
+TEST_F(SpirvTest, AddEmptyEntryPoint) {
+  auto* src = R"()";
+
+  auto* expect = R"(
+[[stage(compute)]]
+fn _tint_unused_entry_point() -> void {
+}
+)";
+
+  auto got = Run<Spirv>(src);
+
+  EXPECT_EQ(expect, str(got));
+}
+
 // Test that different transforms within the sanitizer interact correctly.
 TEST_F(SpirvTest, MultipleTransforms) {
   auto* src = R"(