[SILCombine] Correctly drop debug info when fragmenting an enum

Author: Snowy1803

lib/SILOptimizer/SILCombiner/SILCombinerMiscVisitors.cpp

@@ -573,7 +573,13 @@ bool SILCombiner::optimizeStackAllocatedEnum(AllocStackInst *AS) {
 
   // Second step: replace the enum alloc_stack with a payload alloc_stack.
   auto *newAlloc = Builder.createAllocStack(
-      AS->getLoc(), payloadType, AS->getVarInfo(), AS->hasDynamicLifetime());
+      AS->getLoc(), payloadType, {}, AS->hasDynamicLifetime(), IsNotLexical,
+      IsNotFromVarDecl, DoesNotUseMoveableValueDebugInfo, true);
+  if (auto varInfo = AS->getVarInfo()) {
+    // TODO: Add support for op_enum_fragment
+    // For now, we can't represent this variable correctly, so we drop it.
+    Builder.createDebugValue(AS->getLoc(), SILUndef::get(AS), *varInfo);
+  }
 
   while (!AS->use_empty()) {
     Operand *use = *AS->use_begin();
@@ -610,11 +616,9 @@ bool SILCombiner::optimizeStackAllocatedEnum(AllocStackInst *AS) {
         break;
       }
       case SILInstructionKind::DebugValueInst:
-        if (DebugValueInst::hasAddrVal(user)) {
-          eraseInstFromFunction(*user);
-          break;
-        }
-        LLVM_FALLTHROUGH;
+        // TODO: Add support for op_enum_fragment
+        use->set(SILUndef::get(AS));
+        break;
       default:
         llvm_unreachable("unexpected alloc_stack user");
     }

test/DebugInfo/sil_combine.sil

@@ -25,4 +25,49 @@ bb0(%0 : $Builtin.RawPointer):
   return %ptr : $Builtin.RawPointer
 }
 
+public struct S {}
+public struct C {
+  var x: MP
+}
+
+enum MP {
+  case A(S)
+  case B(S)
+}
+
+// CHECK-LABEL: sil @expand_alloc_stack_of_enum_without_take
+// CHECK:        [[A:%[0-9]+]] = alloc_stack $S
+// CHECK-NOT:      name "a"
+// CHECK-NEXT:   debug_value undef : $*MP, let, name "a", expr op_fragment:#C.x
+// CHECK-NEXT:   debug_value undef : $*MP, let, name "b"
+// CHECK:      bb1:
+// CHECK-NEXT:   store %0 to [[A]]
+// CHECK:      bb2:
+// CHECK-NEXT:   store %0 to [[A]]
+// CHECK:      bb3:
+// CHECK:        destroy_addr [[A]]
+// CHECK: } // end sil function 'expand_alloc_stack_of_enum_without_take'
+sil @expand_alloc_stack_of_enum_without_take : $@convention(method) (S) -> () {
+bb0(%0 : $S):
+  %1 = alloc_stack $MP, let, name "a", expr op_fragment:#C.x
+  debug_value %1 : $*MP, let, name "b", expr op_deref
+  cond_br undef, bb1, bb2
+bb1:
+  %2 = init_enum_data_addr %1 : $*MP, #MP.A!enumelt
+  store %0 to %2 : $*S
+  inject_enum_addr %1 : $*MP, #MP.A!enumelt
+  br bb3
+bb2:
+  %3 = init_enum_data_addr %1 : $*MP, #MP.A!enumelt
+  store %0 to %3 : $*S
+  inject_enum_addr %1 : $*MP, #MP.A!enumelt
+  br bb3
+bb3:
+  destroy_addr %1 : $*MP
+  dealloc_stack %1 : $*MP
+  %11 = tuple ()
+  return %11 : $()
+}
+
+
 // CHECK-IR: ![[DBG_VAR]] = !DILocalVariable(name: "hello"