[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 +1,24 @@
+// 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 remove the local store that is not read.
+//
+// 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 : $()
+}