From 1ae74842cd1be37a8d99d0865623ef16432d3b67 Mon Sep 17 00:00:00 2001
From: Pavel Labath <labath@google.com>
Date: Fri, 6 Sep 2013 08:12:48 +0000
Subject: [PATCH] Avoid double edges when constructing CFGs

Summary:
If a noreturn destructor is executed while returning a value from a function,
the resulting CFG has had two edges to the exit block. This crashed the analyzer,
because it expects that blocks with no terminators have only one outgoing edge.
I added code to avoid creating the second edge in this case.

PS: The crashes did not manifest themselves always, as usually the
NoReturnFunctionChecker would stop program evaluation before the analyzer hit
the assertion, but in the case of lifetime extended temporaries, the checker
failed to do that (which is a separate bug in itself).

Reviewers: jordan_rose

CC: cfe-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D1513

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@190125 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/CFG.cpp  |  7 +++++--
 test/Analysis/cfg.cpp | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/lib/Analysis/CFG.cpp b/lib/Analysis/CFG.cpp
index 5e03f4377d..191c324b3c 100644
--- a/lib/Analysis/CFG.cpp
+++ b/lib/Analysis/CFG.cpp
@@ -1899,9 +1899,12 @@ CFGBlock *CFGBuilder::VisitReturnStmt(ReturnStmt *R) {
   // Create the new block.
   Block = createBlock(false);
 
-  // The Exit block is the only successor.
   addAutomaticObjDtors(ScopePos, LocalScope::const_iterator(), R);
-  addSuccessor(Block, &cfg->getExit());
+
+  // If the one of the destructors does not return, we already have the Exit
+  // block as a successor.
+  if (!Block->hasNoReturnElement())
+    addSuccessor(Block, &cfg->getExit());
 
   // Add the return statement to the block.  This may create new blocks if R
   // contains control-flow (short-circuit operations).
diff --git a/test/Analysis/cfg.cpp b/test/Analysis/cfg.cpp
index 243e1aed99..660d1f2646 100644
--- a/test/Analysis/cfg.cpp
+++ b/test/Analysis/cfg.cpp
@@ -144,3 +144,40 @@ void test_deleteArraydtor() {
   A *a = new A[5];
   delete[] a;
 }
+
+
+namespace NoReturnSingleSuccessor {
+  struct A {
+    A();
+    ~A();
+  };
+
+  struct B : public A {
+    B();
+    ~B() __attribute__((noreturn));
+  };
+
+// CHECK: ENTRY
+// CHECK: 1: 1
+// CHECK-NEXT: 2: return
+// CHECK-NEXT: ~B() (Implicit destructor)
+// CHECK-NEXT: Preds (1)
+// CHECK-NEXT: Succs (1): B0
+  int test1(int *x) {
+    B b;
+    if (x)
+      return 1;
+  }
+
+// CHECK: ENTRY
+// CHECK: 1: 1
+// CHECK-NEXT: 2: return
+// CHECK-NEXT: destructor
+// CHECK-NEXT: Preds (1)
+// CHECK-NEXT: Succs (1): B0
+  int test2(int *x) {
+    const A& a = B();
+    if (x)
+      return 1;
+  }
+}
-- 
2.40.0