[DebugInfo] Salvage Debug Info in Swift Function Passes

Salvage Debug Info was only being called for simplifications, and not
for function passes written in Swift. Salvage Debug Info is now called
for both cases.

Author: Snowy1803

lib/SILOptimizer/SILCombiner/SILCombine.cpp

@@ -615,6 +615,7 @@ void SwiftPassInvocation::eraseInstruction(SILInstruction *inst) {
   if (silCombiner) {
     silCombiner->eraseInstFromFunction(*inst);
   } else {
+    swift::salvageDebugInfo(inst);
     if (inst->isStaticInitializerInst()) {
       inst->getParent()->erase(inst, *getPassManager()->getModule());
     } else {

test/DebugInfo/dead-store-elimination.sil

@@ -0,0 +1,26 @@
+// RUN: %target-sil-opt %s -dead-store-elimination -enable-sil-verify-all | %FileCheck %s
+
+// REQUIRES: swift_in_compiler
+
+sil_stage canonical
+
+import Swift
+import Builtin
+
+// We should be able to replace the local store with a debug_value.
+// The dead store elimination pass is written in Swift, and should call
+// salvage debug info when removing the store.
+
+// CHECK-LABEL: @trivial_local_dead_store
+// CHECK: debug_value %{{[0-9]+}} : $Int, var, name "a"
+// CHECK: return
+sil hidden @trivial_local_dead_store : $@convention(thin) () -> () {
+bb0:
+  %0 = alloc_stack $Int, var, name "a"
+  %1 = integer_literal $Builtin.Int64, 1
+  %2 = struct $Int (%1 : $Builtin.Int64)
+  store %2 to %0 : $*Int
+  %4 = tuple ()
+  dealloc_stack %0 : $*Int
+  return %4 : $()
+}