SILGen: Clean up invariants around capture lists

Author: slavapestov

include/swift/SIL/TypeLowering.h

@@ -946,24 +946,6 @@ class TypeConverter {
   CaptureInfo getLoweredLocalCaptures(SILDeclRef fn);
   bool hasLoweredLocalCaptures(SILDeclRef fn);
 
-#ifndef NDEBUG
-  /// If \c false, \c childDC is in a context it cannot capture variables from,
-  /// so it is expected that Sema may not have computed its \c CaptureInfo.
-  ///
-  /// This call exists for use in assertions; do not use it to skip capture
-  /// processing.
-  static bool canCaptureFromParent(DeclContext *childDC) {
-    // This call was added because Sema leaves the captures of functions that
-    // cannot capture anything uncomputed.
-    // TODO: Make Sema set them to CaptureInfo::empty() instead.
-
-    if (childDC)
-      if (auto decl = childDC->getAsDecl())
-         return decl->getDeclContext()->isLocalContext();
-    return true;
-  }
-#endif
-
   enum class ABIDifference : uint8_t {
     // Types have compatible calling conventions and representations, so can
     // be trivially bitcast.

lib/SIL/TypeLowering.cpp

@@ -2172,6 +2172,20 @@ CaptureInfo
 TypeConverter::getLoweredLocalCaptures(SILDeclRef fn) {
   PrettyStackTraceSILLocation stack("getting lowered local captures",
                                     fn.getAsRegularLocation(), Context);
+  // If we're guaranteed to never have local captures, bail out now.
+  switch (fn.kind) {
+  case SILDeclRef::Kind::StoredPropertyInitializer:
+  case SILDeclRef::Kind::PropertyWrapperBackingInitializer:
+    return CaptureInfo::empty();
+
+  default:
+    if (fn.hasDecl()) {
+      if (!fn.getDecl()->isLocalCapture())
+        return CaptureInfo::empty();
+    }
+
+    break;
+  }
 
   fn.isForeign = 0;
   fn.isCurried = 0;
@@ -2199,8 +2213,7 @@ TypeConverter::getLoweredLocalCaptures(SILDeclRef fn) {
   std::function<void (SILDeclRef)> collectConstantCaptures;
 
   collectCaptures = [&](CaptureInfo captureInfo, DeclContext *dc) {
-    assert(captureInfo.hasBeenComputed() ||
-           !TypeConverter::canCaptureFromParent(dc));
+    assert(captureInfo.hasBeenComputed());
 
     if (captureInfo.hasGenericParamCaptures())
       capturesGenericParams = true;
@@ -2325,6 +2338,9 @@ TypeConverter::getLoweredLocalCaptures(SILDeclRef fn) {
   };
 
   collectFunctionCaptures = [&](AnyFunctionRef curFn) {
+    if (!curFn.getBody())
+      return;
+
     if (!visitedFunctions.insert(curFn).second)
       return;
 
@@ -2392,15 +2408,6 @@ TypeConverter::getLoweredLocalCaptures(SILDeclRef fn) {
     resultingCaptures.push_back(*selfCapture);
   }
 
-  // It is an error for a member of a nominal type to have any captures
-  // at all. If we just clear them out here, SILGen will diagnose the
-  // problem.
-  if (fn.hasDecl()) {
-    auto *dc = fn.getDecl()->getDeclContext();
-    if (dc->isTypeContext())
-      resultingCaptures.clear();
-  }
-
   // Cache the uniqued set of transitive captures.
   CaptureInfo info{Context, resultingCaptures, capturesDynamicSelf,
                    capturesOpaqueValue, capturesGenericParams};

lib/SILGen/SILGenFunction.cpp

@@ -695,31 +695,6 @@ void SILGenFunction::emitArtificialTopLevel(ClassDecl *mainClass) {
   }
 }
 
-#ifndef NDEBUG
-/// If \c false, \c function is either a declaration that inherently cannot
-/// capture variables, or it is in a context it cannot capture variables from.
-/// In either case, it is expected that Sema may not have computed its
-/// \c CaptureInfo.
-///
-/// This call exists for use in assertions; do not use it to skip capture
-/// processing.
-static bool canCaptureFromParent(SILDeclRef function) {
-  switch (function.kind) {
-  case SILDeclRef::Kind::StoredPropertyInitializer:
-  case SILDeclRef::Kind::PropertyWrapperBackingInitializer:
-    return false;
-
-  default:
-    if (function.hasDecl()) {
-      if (auto dc = dyn_cast<DeclContext>(function.getDecl())) {
-        return TypeConverter::canCaptureFromParent(dc);
-      }
-    }
-    return false;
-  }
-}
-#endif
-
 void SILGenFunction::emitGeneratorFunction(SILDeclRef function, Expr *value,
                                            bool EmitProfilerIncrement) {
   auto *dc = function.getDecl()->getInnermostDeclContext();
@@ -757,14 +732,7 @@ void SILGenFunction::emitGeneratorFunction(SILDeclRef function, Expr *value,
     params = ParameterList::create(ctx, SourceLoc(), {param}, SourceLoc());
   }
 
-  CaptureInfo captureInfo;
-  if (function.getAnyFunctionRef())
-    captureInfo = SGM.M.Types.getLoweredLocalCaptures(function);
-  else {
-    assert(!canCaptureFromParent(function));
-    captureInfo = CaptureInfo::empty();
-  }
-
+  auto captureInfo = SGM.M.Types.getLoweredLocalCaptures(function);
   auto interfaceType = value->getType()->mapTypeOutOfContext();
   emitProlog(captureInfo, params, /*selfParam=*/nullptr,
              dc, interfaceType, /*throws=*/false, SourceLoc());

lib/SILGen/SILGenProlog.cpp

@@ -445,8 +445,7 @@ void SILGenFunction::emitProlog(CaptureInfo captureInfo,
 
   // Emit the capture argument variables. These are placed last because they
   // become the first curry level of the SIL function.
-  assert((captureInfo.hasBeenComputed() ||
-          !TypeConverter::canCaptureFromParent(DC)) &&
+  assert(captureInfo.hasBeenComputed() &&
          "can't emit prolog of function with uncomputed captures");
   for (auto capture : captureInfo.getCaptures()) {
     if (capture.isDynamicSelfMetadata()) {