[IRGen] Always apply error value mapping properly for direct returning typed throws

rdar://130783369

The missing mapping causes the wrong element to be used when the offsets are different.

Author: drexin

lib/IRGen/GenCall.cpp

@@ -2848,7 +2848,8 @@ class SyncCallEmission final : public CallEmission {
             errorExplosion.add(elt);
           }
         } else {
-          errorExplosion.add(convertIfNecessary(combined.combinedTy, values[0]));
+          errorExplosion.add(convertIfNecessary(
+              combined.combinedTy, values[combined.errorValueMapping[0]]));
         }
 
         typedErrorExplosion =

test/IRGen/typed_throws.swift

@@ -88,3 +88,26 @@ func testit() throws (S) {
 public struct TypeH {
   public var method: (Int) throws(MyBigError) -> String
 }
+
+struct SmallError: Error {
+  let x: Int
+}
+
+@inline(never)
+func throwsSmallError() throws(SmallError) -> (Float, Int) {
+  throw SmallError(x: 1)
+}
+
+// CHECK: define hidden swiftcc i64 @"$s12typed_throws17catchesSmallErrorSiyF"()
+// CHECK:   [[RES:%.*]] = call swiftcc { float, i64 } @"$s12typed_throws0B10SmallErrorSf_SityAA0cD0VYKF"(ptr swiftself undef, ptr noalias nocapture swifterror dereferenceable(8) %swifterror)
+// CHECK:   [[R0:%.*]] = extractvalue { float, i64 } [[RES]], 0
+// CHECK:   [[R1:%.*]] = extractvalue { float, i64 } [[RES]], 1
+// CHECK:   phi i64 [ [[R1]], %typed.error.load ]
+// CHECK: }
+func catchesSmallError() -> Int {
+  do {
+    return try throwsSmallError().1
+  } catch {
+    return error.x
+  }
+}