[DebugInfo] Set the autogenerated bit to request recycled locations

IRGenDebugInfo expects to see an autogenerated bit before allowing reuse
of the last seen debug location for a new instruction.

rdar://28544248

Author: vedantk

lib/IRGen/IRGenSIL.cpp

@@ -1789,8 +1789,11 @@ void IRGenSILFunction::visitSILBasicBlock(SILBasicBlock *BB) {
         auto Prev = --I.getIterator();
         if (Prev != BB->end())
           DS = Prev->getDebugScope();
-        // Use an artificial (line 0) location.
-        IGM.DebugInfo->setCurrentLoc(Builder, DS, None);
+
+        // Use an artificial (line 0) location, to indicate we'd like to
+        // reuse the last debug loc.
+        IGM.DebugInfo->setCurrentLoc(
+            Builder, DS, RegularLocation::getAutoGeneratedLocation());
       }
 
       if (isa<TermInst>(&I))

test/DebugInfo/returnlocation.swift

@@ -178,3 +178,18 @@ public func cleanup_simple_complex(_ a: NSString) -> Int64 {
 }
 
 // ---------------------------------------------------------------------
+
+// RUN: %FileCheck %s --check-prefix=CHECK_INIT < %t.ll
+// CHECK_INIT: define {{.*}}$S4main6Class1CACSgycfc
+public class Class1 {
+  public required init?() {
+    print("hello")
+    // CHECK_INIT: call {{.*}}@"$Ss5print_9separator10terminatoryypd_S2StF"{{.*}}, !dbg [[printLoc:![0-9]+]]
+    // CHECK_INIT-NEXT: call void @swift_bridgeObjectRelease{{.*}}, !dbg [[retnLoc:![0-9]+]]
+    // CHECK_INIT: br label {{.*}}, !dbg [[retnLoc]]
+
+    // CHECK_INIT: [[printLoc]] = !DILocation(line: [[@LINE-5]]
+    // CHECK_INIT: [[retnLoc]] = !DILocation(line: [[@LINE+1]]
+    return nil
+  }
+}