tint::transform::SingleEntryPoint: Preserve global 'const's

These can be used in all sorts of places which are not tracked by sem::Function::TransitivelyReferencedGlobals().
As they're not emitted as variables by any backend, just preserve them.

Fixed: tint:1598
Change-Id: I2696486cb2ffe8408bd5dd3090d7d600ca1d170f
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/101481
Reviewed-by: Dan Sinclair <dsinclair@chromium.org>
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>
Auto-Submit: Ben Clayton <bclayton@google.com>

src/tint/transform/single_entry_point.cc

@@ -86,11 +86,17 @@ void SingleEntryPoint::Run(CloneContext& ctx, const DataMap& inputs, DataMap&) c
                     ctx.dst->AST().AddGlobalVariable(ctx.Clone(override));
                 }
             },
-            [&](const ast::Variable* v) {  // var, let
-                if (referenced_vars.count(v)) {
-                    ctx.dst->AST().AddGlobalVariable(ctx.Clone(v));
+            [&](const ast::Var* var) {
+                if (referenced_vars.count(var)) {
+                    ctx.dst->AST().AddGlobalVariable(ctx.Clone(var));
                 }
             },
+            [&](const ast::Const* c) {
+                // Always keep 'const' declarations, as these can be used by attributes and array
+                // sizes, which are not tracked as transitively used by functions. They also don't
+                // typically get emitted by the backend unless they're actually used.
+                ctx.dst->AST().AddGlobalVariable(ctx.Clone(c));
+            },
             [&](const ast::Function* func) {
                 if (sem.Get(func)->HasAncestorEntryPoint(entry_point->symbol)) {
                     ctx.dst->AST().AddFunction(ctx.Clone(func));

src/tint/transform/single_entry_point_test.cc

@@ -217,8 +217,14 @@ fn comp_main2() {
 )";
 
     auto* expect = R"(
+const a : f32 = 1.0;
+
+const b : f32 = 1.0;
+
 const c : f32 = 1.0;
 
+const d : f32 = 1.0;
+
 @compute @workgroup_size(1)
 fn comp_main1() {
   let local_c : f32 = c;
@@ -536,5 +542,28 @@ fn comp_main1() {
     EXPECT_EQ(expect, str(got));
 }
 
+TEST_F(SingleEntryPointTest, GlobalConstUsedAsArraySize) {
+    // See crbug.com/tint/1598
+    auto* src = R"(
+const MY_SIZE = 5u;
+
+type Arr = array<i32, MY_SIZE>;
+
+@fragment
+fn main() {
+}
+)";
+
+    auto* expect = src;
+
+    SingleEntryPoint::Config cfg("main");
+
+    DataMap data;
+    data.Add<SingleEntryPoint::Config>(cfg);
+    auto got = Run<SingleEntryPoint>(src, data);
+
+    EXPECT_EQ(expect, str(got));
+}
+
 }  // namespace
 }  // namespace tint::transform

test/tint/bug/tint/1598.wgsl

@@ -0,0 +1,8 @@
+const MY_SIZE = 5u;
+
+type Arr = array<i32, MY_SIZE>;
+
+@fragment
+fn main() {
+    var a : Arr;
+}

test/tint/bug/tint/1598.wgsl.expected.dxc.hlsl

@@ -0,0 +1,4 @@
+void main() {
+  int a[5] = (int[5])0;
+  return;
+}

test/tint/bug/tint/1598.wgsl.expected.fxc.hlsl

@@ -0,0 +1,4 @@
+void main() {
+  int a[5] = (int[5])0;
+  return;
+}

test/tint/bug/tint/1598.wgsl.expected.glsl

@@ -0,0 +1,11 @@
+#version 310 es
+precision mediump float;
+
+void tint_symbol() {
+  int a[5] = int[5](0, 0, 0, 0, 0);
+}
+
+void main() {
+  tint_symbol();
+  return;
+}

test/tint/bug/tint/1598.wgsl.expected.msl

@@ -0,0 +1,21 @@
+#include <metal_stdlib>
+
+using namespace metal;
+
+template<typename T, size_t N>
+struct tint_array {
+    const constant T& operator[](size_t i) const constant { return elements[i]; }
+    device T& operator[](size_t i) device { return elements[i]; }
+    const device T& operator[](size_t i) const device { return elements[i]; }
+    thread T& operator[](size_t i) thread { return elements[i]; }
+    const thread T& operator[](size_t i) const thread { return elements[i]; }
+    threadgroup T& operator[](size_t i) threadgroup { return elements[i]; }
+    const threadgroup T& operator[](size_t i) const threadgroup { return elements[i]; }
+    T elements[N];
+};
+
+fragment void tint_symbol() {
+  tint_array<int, 5> a = {};
+  return;
+}
+

test/tint/bug/tint/1598.wgsl.expected.spvasm

@@ -0,0 +1,25 @@
+; SPIR-V
+; Version: 1.3
+; Generator: Google Tint Compiler; 0
+; Bound: 12
+; Schema: 0
+               OpCapability Shader
+               OpMemoryModel Logical GLSL450
+               OpEntryPoint Fragment %main "main"
+               OpExecutionMode %main OriginUpperLeft
+               OpName %main "main"
+               OpName %a "a"
+               OpDecorate %_arr_int_uint_5 ArrayStride 4
+       %void = OpTypeVoid
+          %1 = OpTypeFunction %void
+        %int = OpTypeInt 32 1
+       %uint = OpTypeInt 32 0
+     %uint_5 = OpConstant %uint 5
+%_arr_int_uint_5 = OpTypeArray %int %uint_5
+%_ptr_Function__arr_int_uint_5 = OpTypePointer Function %_arr_int_uint_5
+         %11 = OpConstantNull %_arr_int_uint_5
+       %main = OpFunction %void None %1
+          %4 = OpLabel
+          %a = OpVariable %_ptr_Function__arr_int_uint_5 Function %11
+               OpReturn
+               OpFunctionEnd

test/tint/bug/tint/1598.wgsl.expected.wgsl

@@ -0,0 +1,8 @@
+const MY_SIZE = 5u;
+
+type Arr = array<i32, MY_SIZE>;
+
+@fragment
+fn main() {
+  var a : Arr;
+}