[IRGen] Return typed errors directly in synchronous functions when possible

rdar://129359355

This PR implements the basic support for returning typed errors directly and applies it to synchronous functions.

Author: drexin

lib/IRGen/CallEmission.h

@@ -19,6 +19,7 @@
 
 #include "Address.h"
 #include "Callee.h"
+#include "Explosion.h"
 #include "Temporary.h"
 
 namespace llvm {
@@ -88,6 +89,7 @@ class CallEmission {
 
   unsigned IndirectTypedErrorArgIdx = 0;
 
+  std::optional<Explosion> typedErrorExplosion;
 
   virtual void setFromCallee();
   void emitToUnmappedMemory(Address addr);
@@ -123,6 +125,10 @@ class CallEmission {
     return CurCallee.getSubstitutions();
   }
 
+  std::optional<Explosion> &getTypedErrorExplosion() {
+    return typedErrorExplosion;
+  }
+
   virtual void begin();
   virtual void end();
   virtual SILType getParameterType(unsigned index) = 0;