writer/spirv: Add Flat decoration to integers

Vulkan requires that shader inputs/outputs that are integers must be
decorated with Flat.

Bug: tint:746, dawn:956
Change-Id: I648451b9aa559d08415bada904dee5f9d1e4e60f
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/56400
Auto-Submit: James Price <jrprice@google.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: James Price <jrprice@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>

src/writer/spirv/builder.cc

@@ -848,8 +848,14 @@ bool Builder::GenerateGlobalVariable(ast::Variable* var) {
       push_annot(spv::Op::OpDecorate,
                  {Operand::Int(var_id), Operand::Int(SpvDecorationLocation),
                   Operand::Int(location->value())});
+      if (type->is_integer_scalar_or_vector()) {
+        // Vulkan requires that integers are always decorated with `Flat`.
+        AddInterpolationDecorations(var_id, ast::InterpolationType::kFlat,
+                                    ast::InterpolationSampling::kNone);
+      }
     } else if (auto* interpolate = deco->As<ast::InterpolateDecoration>()) {
-      AddInterpolationDecorations(var_id, interpolate);
+      AddInterpolationDecorations(var_id, interpolate->type(),
+                                  interpolate->sampling());
     } else if (auto* binding = deco->As<ast::BindingDecoration>()) {
       push_annot(spv::Op::OpDecorate,
                  {Operand::Int(var_id), Operand::Int(SpvDecorationBinding),
@@ -4011,10 +4017,10 @@ SpvBuiltIn Builder::ConvertBuiltin(ast::Builtin builtin,
   return SpvBuiltInMax;
 }
 
-void Builder::AddInterpolationDecorations(
-    uint32_t id,
-    ast::InterpolateDecoration* interpolate) {
-  switch (interpolate->type()) {
+void Builder::AddInterpolationDecorations(uint32_t id,
+                                          ast::InterpolationType type,
+                                          ast::InterpolationSampling sampling) {
+  switch (type) {
     case ast::InterpolationType::kLinear:
       push_annot(spv::Op::OpDecorate,
                  {Operand::Int(id), Operand::Int(SpvDecorationNoPerspective)});
@@ -4026,7 +4032,7 @@ void Builder::AddInterpolationDecorations(
     case ast::InterpolationType::kPerspective:
       break;
   }
-  switch (interpolate->sampling()) {
+  switch (sampling) {
     case ast::InterpolationSampling::kCentroid:
       push_annot(spv::Op::OpDecorate,
                  {Operand::Int(id), Operand::Int(SpvDecorationCentroid)});

src/writer/spirv/builder.h

@@ -212,9 +212,11 @@ class Builder {
   /// Converts an interpolate attribute to SPIR-V decorations and pushes a
   /// capability if needed.
   /// @param id the id to decorate
-  /// @param interpolate the interpolation attribute to convert
+  /// @param type the interpolation type
+  /// @param sampling the interpolation sampling
   void AddInterpolationDecorations(uint32_t id,
-                                   ast::InterpolateDecoration* interpolate);
+                                   ast::InterpolationType type,
+                                   ast::InterpolationSampling sampling);
 
   /// Generates a label for the given id. Emits an error and returns false if
   /// we're currently outside a function.

src/writer/spirv/builder_entry_point_test.cc

@@ -133,6 +133,7 @@ OpName %10 "tint_symbol_3"
 OpName %11 "tint_symbol_1"
 OpName %14 "frag_main"
 OpDecorate %1 Location 0
+OpDecorate %1 Flat
 OpDecorate %4 Location 0
 %3 = OpTypeInt 32 0
 %2 = OpTypePointer Input %3