Add a pass to eliminate access markers.

Author: atrick

include/swift/SIL/SILFunction.h

@@ -642,11 +642,14 @@ class SILFunction
   const BlockListType &getBlocks() const { return BlockList; }
 
   typedef BlockListType::iterator iterator;
+  typedef BlockListType::reverse_iterator reverse_iterator;
   typedef BlockListType::const_iterator const_iterator;
 
   bool empty() const { return BlockList.empty(); }
   iterator begin() { return BlockList.begin(); }
   iterator end() { return BlockList.end(); }
+  reverse_iterator rbegin() { return BlockList.rbegin(); }
+  reverse_iterator rend() { return BlockList.rend(); }
   const_iterator begin() const { return BlockList.begin(); }
   const_iterator end() const { return BlockList.end(); }
   unsigned size() const { return BlockList.size(); }

include/swift/SILOptimizer/PassManager/Passes.def

@@ -54,6 +54,8 @@ PASS(AADumper, "aa-dump",
      "Dump Alias Analysis over all Pairs")
 PASS(ABCOpt, "abcopts",
      "Array Bounds Check Optimization")
+PASS(AccessMarkerElimination, "access-marker-elim",
+     "Access Marker Elimination.")
 PASS(AddressLowering, "address-lowering",
      "SIL Address Lowering")
 PASS(AllocBoxToStack, "allocbox-to-stack",

lib/SILOptimizer/Mandatory/AccessMarkerElimination.cpp

@@ -0,0 +1,73 @@
+//===--- AccessMarkerElimination.cpp - Eliminate access markers. ----------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+///
+/// This pass eliminates the instructions that demarcate memory access regions.
+/// If no memory access markers exist, then the pass does nothing. Otherwise, it
+/// unconditionally eliminates the markers.
+/// 
+/// This is an always-on pass for temporary bootstrapping. It allows running
+/// test cases through the pipeline and exercising SIL verification before all
+/// passes support access markers.
+///
+/// TODO: DefiniteInitialization needs to be fixed to handle begin/end_access.
+/// The immediate goal is to run this pass only at -O. Access markers should not
+/// interfere with any -Onone passes.
+///
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "access-marker-elim"
+#include "swift/Basic/Range.h"
+#include "swift/SIL/SILFunction.h"
+#include "swift/SILOptimizer/PassManager/Transforms.h"
+
+using namespace swift;
+
+namespace {
+
+struct AccessMarkerElimination : SILModuleTransform {
+  void run() override {
+    for (auto &F : *getModule()) {
+      // If the function has no access markers, don't invalidate any analyses.
+      if (!F.hasAccessMarkers())
+        continue;
+      
+      F.disableAccessMarkers();
+
+      // iterating in reverse eliminates more begin_access users before they
+      // need to be replaced.
+      for (auto &BB : reversed(F)) {
+        for (auto II = BB.rbegin(), IE = BB.rend(); II != IE;) {
+          SILInstruction *inst = &*II;
+          ++II;
+
+          if (auto beginAccess = dyn_cast<BeginAccessInst>(inst)) {
+            beginAccess->replaceAllUsesWith(beginAccess->getSource());
+            beginAccess->eraseFromParent();
+          }
+          if (auto endAccess = dyn_cast<EndAccessInst>(inst)) {
+            assert(endAccess->use_empty());
+            endAccess->eraseFromParent();
+          }
+        }
+      }
+
+      auto InvalidKind = SILAnalysis::InvalidationKind::Instructions;
+      invalidateAnalysis(&F, InvalidKind);
+    }
+  }
+};
+
+} // end anonymous namespace
+
+SILTransform *swift::createAccessMarkerElimination() {
+  return new AccessMarkerElimination();
+}

lib/SILOptimizer/Mandatory/CMakeLists.txt

@@ -1,4 +1,5 @@
 set(MANDATORY_SOURCES
+  Mandatory/AccessMarkerElimination.cpp
   Mandatory/AddressLowering.cpp
   Mandatory/DefiniteInitialization.cpp
   Mandatory/DIMemoryUseCollector.cpp

lib/SILOptimizer/PassManager/PassPipeline.cpp

@@ -82,6 +82,7 @@ static void addMandatoryOptPipeline(SILPassPipelinePlan &P,
 
   P.addOwnershipModelEliminator();
   P.addNoReturnFolding();
+  P.addAccessMarkerElimination();
   P.addDefiniteInitialization();
 
   P.addMandatoryInlining();