[DebugInfo] Fix AllocStackHoisting losing debug info

AllocStackHoisting was losing debug info, including at -Onone.
When two alloc_stacks of the same type are merged, one of them
would lose their debug variable. It is now salvaged, with an added
debug_value.

This case was previously only handled for noncopyable types, it is
now done in all cases.

(cherry picked from commit c02f663)

Author: Snowy1803

lib/IRGen/AllocStackHoisting.cpp

@@ -157,9 +157,8 @@ void moveAllocStackToBeginningOfBlock(
   // of the debug_value to the original position.
   if (haveMovedElt) {
     if (auto varInfo = AS->getVarInfo()) {
-      SILBuilderWithScope Builder(AS);
       // SILBuilderWithScope skips over meta instructions when picking a scope.
-      Builder.setCurrentDebugScope(AS->getDebugScope());
+      SILBuilder Builder(AS, AS->getDebugScope());
       auto *DVI = Builder.createDebugValue(AS->getLoc(), AS, *varInfo);
       DVI->setUsesMoveableValueDebugInfo();
       DebugValueToBreakBlocksAt.push_back(DVI);
@@ -198,14 +197,14 @@ void Partition::assignStackLocation(
     if (AssignedLoc == AllocStack) continue;
     eraseDeallocStacks(AllocStack);
     AllocStack->replaceAllUsesWith(AssignedLoc);
-    if (hasAtLeastOneMovedElt) {
-      if (auto VarInfo = AllocStack->getVarInfo()) {
-        SILBuilderWithScope Builder(AllocStack);
-        auto *DVI = Builder.createDebugValue(AllocStack->getLoc(), AssignedLoc,
-                                             *VarInfo);
+    if (auto VarInfo = AllocStack->getVarInfo()) {
+      SILBuilder Builder(AllocStack, AllocStack->getDebugScope());
+      auto *DVI = Builder.createDebugValueAddr(AllocStack->getLoc(),
+                                               AssignedLoc, *VarInfo);
+      if (hasAtLeastOneMovedElt) {
         DVI->setUsesMoveableValueDebugInfo();
-        DebugValueToBreakBlocksAt.push_back(DVI);
       }
+      DebugValueToBreakBlocksAt.push_back(DVI);
     }
     AllocStack->eraseFromParent();
   }

test/SILOptimizer/allocstack_hoisting_debuginfo.sil

@@ -98,13 +98,14 @@ bb4:
   return %9999 : $()
 }
 
-// This case we are not moving anything so we are leaving in the default
-// behavior which is not breaking blocks and not inserting debug_info.
+// This case we are not moving anything, so we don't add the
+// [moveable_value_debuginfo] flag, but we still want debug info for the
+// second alloc_stack!
 //
 // CHECK-LABEL: sil @hoist_generic_3 :
 // CHECK: bb0([[ARG:%.*]] : $*T,
 // CHECK-NEXT:   [[STACK:%.*]] = alloc_stack $T{{[ ]*}}, let, name "x"
-// CHECK-NOT:    debug_value
+// CHECK:        debug_value %{{.+}}, let, name "y"
 // CHECK: } // end sil function 'hoist_generic_3'
 sil @hoist_generic_3 : $@convention(thin) <T> (@in T, Builtin.Int1) -> () {
 bb0(%0 : $*T, %1: $Builtin.Int1):