MandatoryPerformanceOptimizations: force inlining of transparent co-routines

This might be necessary if `-enable-testing` is turned on, because in this mode function linkages are different than in a regular build.

Author: eeckstein

SwiftCompilerSources/Sources/Optimizer/ModulePasses/MandatoryPerformanceOptimizations.swift

@@ -258,11 +258,13 @@ private func shouldInline(apply: FullApplySite, callee: Function, alreadyInlined
     return false
   }
 
-  if !callee.canBeInlinedIntoCaller(withSerializedKind: apply.parentFunction.serializedKind) &&
-     // Even if the serialization kind doesn't match, we need to make sure to inline witness method thunks
-     // in embedded swift.
-     callee.thunkKind != .thunk
-  {
+  guard callee.canBeInlinedIntoCaller(withSerializedKind: apply.parentFunction.serializedKind) ||
+        // Even if the serialization kind doesn't match, we need to make sure to inline witness method thunks
+        // in embedded swift.
+        callee.thunkKind == .thunk ||
+        // Force inlining transparent co-routines. This might be necessary if `-enable-testing` is turned on.
+        (apply is BeginApplyInst && callee.isTransparent)
+  else {
     return false
   }