[Impeller] Statically check stage interfaces for precision mismatches.

Fixes flutter/flutter#147078

Author: chinmaygarde

impeller/compiler/code_gen_template.h

@@ -88,6 +88,7 @@ struct {{camel_case(shader_name)}}{{camel_case(shader_stage)}}Shader {
     {{stage_input.type.vec_size}}u,     // vec size
     {{stage_input.type.columns}}u,      // number of columns
     {{stage_input.offset}}u,            // offset for interleaved layout
+    {{stage_input.relaxed_precision}},  // relaxed precision
   };
 {% endfor %}
 {% endif %}
@@ -140,7 +141,9 @@ struct {{camel_case(shader_name)}}{{camel_case(shader_stage)}}Shader {
     {{stage_output.type.type_name}},     // type
     {{stage_output.type.bit_width}}u,    // bit width of type
     {{stage_output.type.vec_size}}u,     // vec size
-    {{stage_output.type.columns}}u       // number of columns
+    {{stage_output.type.columns}}u,      // number of columns
+    {{stage_output.offset}}u,            // offset for interleaved layout
+    {{stage_output.relaxed_precision}},  // relaxed precision
   };
 {% endfor %}
   static constexpr std::array<const ShaderStageIOSlot*, {{length(stage_outputs)}}> kAllShaderStageOutputs = {

impeller/compiler/reflector.cc

@@ -655,12 +655,15 @@ std::optional<nlohmann::json::object_t> Reflector::ReflectResource(
       CompilerBackend::ExtendedResourceIndex::kPrimary, resource.id);
   result["ext_res_1"] = compiler_.GetExtendedMSLResourceBinding(
       CompilerBackend::ExtendedResourceIndex::kSecondary, resource.id);
+  result["relaxed_precision"] =
+      compiler_->get_decoration(
+          resource.id, spv::Decoration::DecorationRelaxedPrecision) == 1;
+  result["offset"] = offset.value_or(0u);
   auto type = ReflectType(resource.type_id);
   if (!type.has_value()) {
     return std::nullopt;
   }
   result["type"] = std::move(type.value());
-  result["offset"] = offset.value_or(0u);
   return result;
 }
 

impeller/core/shader_types.h

@@ -119,22 +119,25 @@ struct ShaderStageIOSlot {
   size_t vec_size;
   size_t columns;
   size_t offset;
+  bool relaxed_precision;
 
   constexpr size_t GetHash() const {
     return fml::HashCombine(name, location, set, binding, type, bit_width,
-                            vec_size, columns, offset);
+                            vec_size, columns, offset, relaxed_precision);
   }
 
   constexpr bool operator==(const ShaderStageIOSlot& other) const {
-    return name == other.name &&            //
-           location == other.location &&    //
-           set == other.set &&              //
-           binding == other.binding &&      //
-           type == other.type &&            //
-           bit_width == other.bit_width &&  //
-           vec_size == other.vec_size &&    //
-           columns == other.columns &&      //
-           offset == other.offset;
+    return name == other.name &&                         //
+           location == other.location &&                 //
+           set == other.set &&                           //
+           binding == other.binding &&                   //
+           type == other.type &&                         //
+           bit_width == other.bit_width &&               //
+           vec_size == other.vec_size &&                 //
+           columns == other.columns &&                   //
+           offset == other.offset &&                     //
+           relaxed_precision == other.relaxed_precision  //
+        ;
   }
 };
 

impeller/renderer/shader_stage_compatibility_checker.h

@@ -47,7 +47,8 @@ class ShaderStageCompatibilityChecker {
               input_slot->bit_width != output_slot->bit_width ||
               input_slot->vec_size != output_slot->vec_size ||
               input_slot->columns != output_slot->columns ||
-              input_slot->offset != output_slot->offset) {
+              input_slot->offset != output_slot->offset ||
+              input_slot->relaxed_precision != output_slot->relaxed_precision) {
             return false;
           }
         }