[PATCH] D62507: [Dominators] PR42041: Skip nullpointer successors

[Kristóf Umann via Phabricator via llvm-commits]

Szelethus created this revision.
Szelethus added reviewers: NoQ, MaskRay, xazax.hun, NutshellySima, asbirlea, kuhar.
Szelethus added projects: clang, LLVM.
Herald added subscribers: llvm-commits, gamesh411, kristina, dkrupp, rnkovacs.

https://bugs.llvm.org/show_bug.cgi?id=42041

In Clang's CFG, we use nullpointers to represent unreachable nodes, for
example, in the included testfile, block `B0` is unreachable from block
`B1`, resulting in a nullpointer dereference somewhere in
`llvm::DominatorTreeBase<clang::CFGBlock, false>::recalculate`.

This patch fixes this issue simply by skipping such successors.


Repository:
  rL LLVM

https://reviews.llvm.org/D62507

Files:
  clang/test/Analysis/domtest.cpp
  llvm/include/llvm/Support/GenericDomTreeConstruction.h


Index: llvm/include/llvm/Support/GenericDomTreeConstruction.h
===================================================================
--- llvm/include/llvm/Support/GenericDomTreeConstruction.h
+++ llvm/include/llvm/Support/GenericDomTreeConstruction.h
@@ -235,6 +235,13 @@
       constexpr bool Direction = IsReverse != IsPostDom;  // XOR.
       for (const NodePtr Succ :
            ChildrenGetter<Direction>::Get(BB, BatchUpdates)) {
+
+        // The clang's CFG contains nullpointers for unreachable successors (eg.
+        // an if statement's condition is always false, the 'then' branch is
+        // unreachable), skip them.
+        if (!Succ)
+          continue;
+
         const auto SIT = NodeToInfo.find(Succ);
         // Don't visit nodes more than once but remember to collect
         // ReverseChildren.
Index: clang/test/Analysis/domtest.cpp
===================================================================
--- /dev/null
+++ clang/test/Analysis/domtest.cpp
@@ -0,0 +1,46 @@
+// RUN: %clang_analyze_cc1 %s \
+// RUN:   -analyzer-checker=debug.DumpCFG \
+// RUN:   -analyzer-checker=debug.DumpDominators \
+// RUN:   2>&1 | FileCheck %s
+
+namespace pr42041_unreachable_cfg_successor {
+enum Kind {
+  A
+};
+
+void f() {
+  switch(Kind{}) {
+  case A:
+    break;
+  }
+}
+} // end of namespace pr42041_unreachable_cfg_successor
+
+// CHECK:      void f()
+// CHECK-NEXT:  [B3 (ENTRY)]
+// CHECK-NEXT:    Succs (1): B1
+// 
+// CHECK:       [B1]
+// CHECK-NEXT:    1: {}
+// CHECK-NEXT:    2: pr42041_unreachable_cfg_successor::Kind[B1.1]
+// CHECK-SAME:                    (CXXFunctionalCastExpr, NoOp,
+// CHECK-SAME:                     enum pr42041_unreachable_cfg_successor::Kind)
+// CHECK-NEXT:    3: [B1.2] (ImplicitCastExpr, IntegralCast, int)
+// CHECK-NEXT:    T: switch [B1.3]
+// CHECK-NEXT:    Preds (1): B3
+// CHECK-NEXT:    Succs (2): B2 B0(Unreachable)
+//
+// CHECK:       [B2]
+// CHECK-NEXT:   case A:
+// CHECK-NEXT:    T: break;
+// CHECK-NEXT:    Preds (1): B1
+// CHECK-NEXT:    Succs (1): B0
+//
+// CHECK:       [B0 (EXIT)]
+// CHECK-NEXT:    Preds (2): B2 B1(Unreachable)
+//
+// CHECK:      Immediate dominance tree (Node#,IDom#):
+// CHECK-NEXT: (0,2)
+// CHECK-NEXT: (1,3)
+// CHECK-NEXT: (2,1)
+// CHECK-NEXT: (3,3)


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