[SPIR-V] Result storing

src/xenia/gpu/shader.h

@@ -65,17 +65,17 @@ enum class InstructionStorageTarget {
 // disassembly (because oPts.x000 will be assembled, but oPts.x00_ has both
 // skipped components and zeros, which cannot be encoded, and therefore it will
 // not).
-constexpr uint32_t GetInstructionStorageTargetUsedComponents(
+constexpr uint32_t GetInstructionStorageTargetUsedComponentCount(
     InstructionStorageTarget target) {
   switch (target) {
     case InstructionStorageTarget::kNone:
-      return 0b0000;
+      return 0;
     case InstructionStorageTarget::kPointSizeEdgeFlagKillVertex:
-      return 0b0111;
+      return 3;
     case InstructionStorageTarget::kDepth:
-      return 0b0001;
+      return 1;
     default:
-      return 0b1111;
+      return 4;
   }
 }
 
@@ -136,8 +136,9 @@ struct InstructionResult {
   // Returns the write mask containing only components actually present in the
   // target.
   uint32_t GetUsedWriteMask() const {
-    return original_write_mask &
-           GetInstructionStorageTargetUsedComponents(storage_target);
+    uint32_t target_component_count =
+        GetInstructionStorageTargetUsedComponentCount(storage_target);
+    return original_write_mask & ((1 << target_component_count) - 1);
   }
   // True if the components are in their 'standard' swizzle arrangement (xyzw).
   bool IsStandardSwizzle() const {
@@ -161,6 +162,28 @@ struct InstructionResult {
     }
     return used_components;
   }
+  // Returns which components of the used write mask are constant, and what
+  // values they have.
+  uint32_t GetUsedConstantComponents(uint32_t& constant_values_out) const {
+    uint32_t constant_components = 0;
+    uint32_t constant_values = 0;
+    uint32_t used_write_mask = GetUsedWriteMask();
+    for (uint32_t i = 0; i < 4; ++i) {
+      if (!(used_write_mask & (1 << i))) {
+        continue;
+      }
+      SwizzleSource component = components[i];
+      if (component >= SwizzleSource::kX && component <= SwizzleSource::kW) {
+        continue;
+      }
+      constant_components |= 1 << i;
+      if (component == SwizzleSource::k1) {
+        constant_values |= 1 << i;
+      }
+    }
+    constant_values_out = constant_values;
+    return constant_components;
+  }
 };
 
 enum class InstructionStorageSource {