Remove MSL override generation

This CL removes the override emission from the MSL backend. The
override should be removed by the substitute_override transform
before making it to the backend.

Bug: tint:1155
Change-Id: I9d3852a7e20b258a2f0af200bff6268037eaa0b5
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/101662
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>

src/tint/writer/msl/generator_impl.cc

@@ -271,9 +271,11 @@ bool GeneratorImpl::Generate() {
             [&](const ast::Const*) {
                 return true;  // Constants are embedded at their use
             },
-            [&](const ast::Override* override) {
+            [&](const ast::Override*) {
-                TINT_DEFER(line());
+                // Override is removed with SubstituteOverride
-                return EmitOverride(override);
+                TINT_ICE(Writer, diagnostics_)
+                    << "Override should have been removed by the substitute_override transform.";
+                return false;
             },
             [&](const ast::Function* func) {
                 TINT_DEFER(line());
@@ -3038,22 +3040,6 @@ bool GeneratorImpl::EmitLet(const ast::Let* let) {
     return true;
 }
 
-bool GeneratorImpl::EmitOverride(const ast::Override* override) {
-    auto* global = program_->Sem().Get<sem::GlobalVariable>(override);
-    auto* type = global->Type();
-
-    auto out = line();
-    out << "constant ";
-    if (!EmitType(out, type, program_->Symbols().NameFor(override->symbol))) {
-        return false;
-    }
-    out << " " << program_->Symbols().NameFor(override->symbol);
-
-    out << " [[function_constant(" << global->OverrideId().value << ")]];";
-
-    return true;
-}
-
 GeneratorImpl::SizeAndAlign GeneratorImpl::MslPackedTypeSizeAndAlign(const sem::Type* ty) {
     return Switch(
         ty,

src/tint/writer/msl/generator_impl.h

@@ -356,10 +356,6 @@ class GeneratorImpl : public TextGenerator {
     /// @param let the variable to generate
     /// @returns true if the variable was emitted
     bool EmitLet(const ast::Let* let);
-    /// Handles generating a module-scope 'override' declaration
-    /// @param override the 'override' to emit
-    /// @returns true if the variable was emitted
-    bool EmitOverride(const ast::Override* override);
     /// Emits the zero value for the given type
     /// @param out the output of the expression stream
     /// @param type the type to emit the value for

src/tint/writer/msl/generator_impl_module_constant_test.cc

@@ -328,27 +328,5 @@ void f() {
 )");
 }
 
-TEST_F(MslGeneratorImplTest, Emit_Override) {
-    auto* var = Override("pos", ty.f32(), Expr(3_f), Id(23_a));
-
-    GeneratorImpl& gen = Build();
-
-    ASSERT_TRUE(gen.EmitOverride(var)) << gen.error();
-    EXPECT_EQ(gen.result(), "constant float pos [[function_constant(23)]];\n");
-}
-
-TEST_F(MslGeneratorImplTest, Emit_Override_NoId) {
-    auto* var_a = Override("a", ty.f32(), Id(0_a));
-    auto* var_b = Override("b", ty.f32());
-
-    GeneratorImpl& gen = Build();
-
-    ASSERT_TRUE(gen.EmitOverride(var_a)) << gen.error();
-    ASSERT_TRUE(gen.EmitOverride(var_b)) << gen.error();
-    EXPECT_EQ(gen.result(), R"(constant float a [[function_constant(0)]];
-constant float b [[function_constant(1)]];
-)");
-}
-
 }  // namespace
 }  // namespace tint::writer::msl