SILDebugScopes: Remove a stateful workaround for Property Wrappers.

In an earlier version of the ASTScope -> SILdebugScope translation a workaround
was put into place that would select the current debug scope if an ASTScope was
marked as ignoreInDebugInfo. Removing this workaround makes the translation more
predictable as it eliminated the dependency on the current SILBuilder state. The
property wrapper tests still pass without this.

This uncovers a situations with let bindings where the SIL instructions are
emitted RHS before LHS, which does violate the di-hole verifier. This is
addressed by relaxing the verifier for now.

rdar://108736443

Author: adrian-prantl

lib/SIL/Verifier/SILVerifier.cpp

@@ -6283,6 +6283,15 @@ class SILVerifier : public SILVerifierBase<SILVerifier> {
       // inherit the sourrounding scope in IRGenSIL.
       if (SI.getLoc().getKind() == SILLocation::MandatoryInlinedKind)
         continue;
+      // FIXME: There are situations where the execution legitimately goes
+      //        backwards, such as
+      //
+      //            while case let w: String? = Optional.some("b") {}
+      //
+      //        where the RHS of the assignment gets run first and then the
+      //        result is copied into the LHS.
+      if (!llvm::isa<BeginBorrowInst>(&SI) || !llvm::isa<CopyValueInst>(&SI))
+        continue;
 
       // If we haven't seen this debug scope yet, update the
       // map and go on.

lib/SILGen/SILGenFunction.cpp

@@ -370,20 +370,9 @@ SILGenFunction::getOrCreateScope(const ast_scope::ASTScopeImpl *ASTScope,
   // Decide whether to pick a parent scope instead.
   if (ASTScope->ignoreInDebugInfo()) {
     LLVM_DEBUG(llvm::dbgs() << "ignored\n");
-    // FIXME: it would be more deterministic to use
-    //        getOrCreateScope(ASTScope->getParent().getPtrOrNull());
-    //        here. Unfortunately property wrappers rearrange AST
-    //        nodes without marking them as implicit, e.g.:
-    //
-    //           @Wrapper(a) var v = b
-    //        ->
-    //           let _tmp = Constructor(a, b); var v = _tmp
-    //
-    //        Since the arguments to Constructor aren't marked as implicit,
-    //        argument b is in the scope of v, but the call to Constructor
-    //        isn't, which correctly triggers the scope hole verifier.
-    auto *CurScope = B.getCurrentDebugScope();
-    return CurScope->InlinedCallSite != InlinedAt ? FnScope : CurScope;
+    auto *ParentScope = getOrCreateScope(ASTScope->getParent().getPtrOrNull(),
+                                         FnScope, InlinedAt);
+    return ParentScope->InlinedCallSite != InlinedAt ? FnScope : ParentScope;
   }
 
   // Collapse BraceStmtScopes whose parent is a .*BodyScope.

test/DebugInfo/guard-let-scope3.swift

@@ -0,0 +1,19 @@
+// RUN: %target-swift-frontend -g -emit-sil %s -parse-as-library -module-name a | %FileCheck %s
+public class C {}
+public enum MyError : Error {
+  init() { self.init() }
+}
+public class S {
+  private var c = [Int : C?]()
+  public func f(_ i: Int) throws  -> C {
+    guard let x = c[i], let x else {
+    // CHECK: sil_scope [[X1:[0-9]+]] { loc "{{.*}}":[[@LINE-1]]:5
+    // CHECK: sil_scope [[X2:[0-9]+]] { loc "{{.*}}":[[@LINE-2]]:29
+    // CHECK: debug_value {{.*}} : $Optional<C>, let, name "x", {{.*}}, scope [[X1]]
+    // CHECK: debug_value %29 : $C, let, name "x", {{.*}}, scope [[X2]]
+    // CHECK-NEXT:  scope [[X2]]
+      throw MyError()
+    }
+    return x
+  }
+}