[clang] 9824ec8 - [clang][dataflow] Refactor `DataflowWorklist` types and add a WTO version.

[Yitzhak Mandelbaum via cfe-commits]

Author: Yitzhak Mandelbaum
Date: 2023-08-04T23:29:08Z
New Revision: 9824ec875cecc533d55c1f11c0c0440520c34464

URL: https://github.com/llvm/llvm-project/commit/9824ec875cecc533d55c1f11c0c0440520c34464
DIFF: https://github.com/llvm/llvm-project/commit/9824ec875cecc533d55c1f11c0c0440520c34464.diff

LOG: [clang][dataflow] Refactor `DataflowWorklist` types and add a WTO version.

Removes dependency of the DataflowWorklistBase type on the PostOrderCFGView. The
base had no particular connection to this order -- looks like it was included as
a convenience to the two derived classes rather than because it belonged there
conceptually. Removing it cleans up the base class a bit and makes it suitable
to extension with the new WTODataflowWorklist class.

Differential Revision: https://reviews.llvm.org/D153071

Added: 
    

Modified: 
    clang/include/clang/Analysis/FlowSensitive/DataflowWorklist.h
    clang/unittests/Analysis/CFGTest.cpp

Removed: 
    


################################################################################
diff  --git a/clang/include/clang/Analysis/FlowSensitive/DataflowWorklist.h b/clang/include/clang/Analysis/FlowSensitive/DataflowWorklist.h
index e926adf6f0b2a9..f1d05743bf7f12 100644
--- a/clang/include/clang/Analysis/FlowSensitive/DataflowWorklist.h
+++ b/clang/include/clang/Analysis/FlowSensitive/DataflowWorklist.h
@@ -12,6 +12,7 @@
 #ifndef LLVM_CLANG_ANALYSIS_FLOWSENSITIVE_DATAFLOWWORKLIST_H
 #define LLVM_CLANG_ANALYSIS_FLOWSENSITIVE_DATAFLOWWORKLIST_H
 
+#include "clang/Analysis/Analyses/IntervalPartition.h"
 #include "clang/Analysis/Analyses/PostOrderCFGView.h"
 #include "clang/Analysis/CFG.h"
 #include "llvm/ADT/PriorityQueue.h"
@@ -21,16 +22,13 @@ namespace clang {
 /// on the order defined by 'Comp'.
 template <typename Comp, unsigned QueueSize> class DataflowWorklistBase {
   llvm::BitVector EnqueuedBlocks;
-  PostOrderCFGView *POV;
   llvm::PriorityQueue<const CFGBlock *,
                       SmallVector<const CFGBlock *, QueueSize>, Comp>
       WorkList;
 
 public:
-  DataflowWorklistBase(const CFG &Cfg, PostOrderCFGView *POV, Comp C)
-      : EnqueuedBlocks(Cfg.getNumBlockIDs()), POV(POV), WorkList(C) {}
-
-  const PostOrderCFGView *getCFGView() const { return POV; }
+  DataflowWorklistBase(const CFG &Cfg, Comp C)
+      : EnqueuedBlocks(Cfg.getNumBlockIDs()), WorkList(C) {}
 
   void enqueueBlock(const CFGBlock *Block) {
     if (Block && !EnqueuedBlocks[Block->getBlockID()]) {
@@ -62,7 +60,7 @@ struct ReversePostOrderCompare {
 struct ForwardDataflowWorklist
     : DataflowWorklistBase<ReversePostOrderCompare, 20> {
   ForwardDataflowWorklist(const CFG &Cfg, PostOrderCFGView *POV)
-      : DataflowWorklistBase(Cfg, POV,
+      : DataflowWorklistBase(Cfg,
                              ReversePostOrderCompare{POV->getComparator()}) {}
 
   ForwardDataflowWorklist(const CFG &Cfg, AnalysisDeclContext &Ctx)
@@ -74,6 +72,19 @@ struct ForwardDataflowWorklist
   }
 };
 
+/// A worklist implementation for forward dataflow analysis based on a weak
+/// topological ordering of the nodes. The worklist cannot contain the same
+/// block multiple times at once.
+struct WTODataflowWorklist : DataflowWorklistBase<WTOCompare, 20> {
+  WTODataflowWorklist(const CFG &Cfg, const WTOCompare &Cmp)
+      : DataflowWorklistBase(Cfg, Cmp) {}
+
+  void enqueueSuccessors(const CFGBlock *Block) {
+    for (auto B : Block->succs())
+      enqueueBlock(B);
+  }
+};
+
 /// A worklist implementation for backward dataflow analysis. The enqueued
 /// block will be dequeued in post order. The worklist cannot contain the same
 /// block multiple times at once.
@@ -81,8 +92,7 @@ struct BackwardDataflowWorklist
     : DataflowWorklistBase<PostOrderCFGView::BlockOrderCompare, 20> {
   BackwardDataflowWorklist(const CFG &Cfg, AnalysisDeclContext &Ctx)
       : DataflowWorklistBase(
-            Cfg, Ctx.getAnalysis<PostOrderCFGView>(),
-            Ctx.getAnalysis<PostOrderCFGView>()->getComparator()) {}
+            Cfg, Ctx.getAnalysis<PostOrderCFGView>()->getComparator()) {}
 
   void enqueuePredecessors(const CFGBlock *Block) {
     for (auto B : Block->preds())

diff  --git a/clang/unittests/Analysis/CFGTest.cpp b/clang/unittests/Analysis/CFGTest.cpp
index 7ce35e3fe4a4f4..9fa034a0e472e9 100644
--- a/clang/unittests/Analysis/CFGTest.cpp
+++ b/clang/unittests/Analysis/CFGTest.cpp
@@ -6,13 +6,15 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "clang/Analysis/CFG.h"
 #include "CFGBuildResult.h"
 #include "clang/AST/Decl.h"
 #include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/Analysis/Analyses/IntervalPartition.h"
 #include "clang/Analysis/AnalysisDeclContext.h"
-#include "clang/Analysis/CFG.h"
 #include "clang/Analysis/FlowSensitive/DataflowWorklist.h"
 #include "clang/Tooling/Tooling.h"
+#include "gmock/gmock.h"
 #include "gtest/gtest.h"
 #include <algorithm>
 #include <string>
@@ -244,6 +246,8 @@ TEST(CFG, ElementRefIterator) {
 TEST(CFG, Worklists) {
   const char *Code = "int f(bool cond) {\n"
                      "  int a = 5;\n"
+                     "  while (a < 6)\n"
+                     "    ++a;\n"
                      "  if (cond)\n"
                      "    a += 1;\n"
                      "  return a;\n"
@@ -272,6 +276,30 @@ TEST(CFG, Worklists) {
                            ForwardNodes.begin()));
   }
 
+  // RPO: 876321054
+  // WTO: 876534210
+  // So, we construct the WTO order accordingly from the reference order.
+  std::vector<const CFGBlock *> WTOOrder = {
+      ReferenceOrder[0], ReferenceOrder[1], ReferenceOrder[2],
+      ReferenceOrder[7], ReferenceOrder[3], ReferenceOrder[8],
+      ReferenceOrder[4], ReferenceOrder[5], ReferenceOrder[6]};
+
+  {
+    using ::testing::ElementsAreArray;
+    std::optional<WeakTopologicalOrdering> WTO = getIntervalWTO(*CFG);
+    ASSERT_TRUE(WTO);
+    WTOCompare WCmp(*WTO);
+    WTODataflowWorklist WTOWorklist(*CFG, WCmp);
+    for (const auto *B : *CFG)
+      WTOWorklist.enqueueBlock(B);
+
+    std::vector<const CFGBlock *> WTONodes;
+    while (const CFGBlock *B = WTOWorklist.dequeue())
+      WTONodes.push_back(B);
+
+    EXPECT_THAT(WTONodes, ElementsAreArray(WTOOrder));
+  }
+
   std::reverse(ReferenceOrder.begin(), ReferenceOrder.end());
 
   {