From 86e18055e607b257c6867e444a4e598cb8f812b8 Mon Sep 17 00:00:00 2001
From: Jonas Devlieghere <jonas@devlieghere.com>
Date: Wed, 1 Aug 2018 10:24:17 +0000
Subject: [DebugInfo] Have custom std::reverse_iterator<DWARFDie>

The DWARFDie is a lightweight utility wrapper that stores a pointer to a
compile unit and a debug info entry. Currently, its iterator (used for
walking over its children) stores a DWARFDie and returns a const
reference when dereferencing it.

When the iterator is modified (by incrementing or decrementing it), this
reference becomes invalid. This was happening when calling reverse on
it, because the std::reverse_iterator is keeping a temporary copy of the
iterator (see
https://en.cppreference.com/w/cpp/iterator/reverse_iterator for a good
illustration).

The relevant code in libcxx:

  reference operator*() const {_Iter __tmp = current; return *--__tmp;}

When dereferencing the reverse iterator, we decrement and return a
reference to a DWARFDie stored in the stack frame of this function,
resulting in UB at runtime.

This patch specifies the std::reverse_iterator for DWARFDie to do the
right thing.

Differential revision: https://reviews.llvm.org/D49679

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@338506 91177308-0d34-0410-b5e6-96231b3b80d8
---
 unittests/DebugInfo/DWARF/DWARFDebugInfoTest.cpp | 71 +++++++++++++++++-------
 1 file changed, 51 insertions(+), 20 deletions(-)

(limited to 'unittests')

diff --git a/unittests/DebugInfo/DWARF/DWARFDebugInfoTest.cpp b/unittests/DebugInfo/DWARF/DWARFDebugInfoTest.cpp
index 442dea3c52f..273809fcbd3 100644
--- a/unittests/DebugInfo/DWARF/DWARFDebugInfoTest.cpp
+++ b/unittests/DebugInfo/DWARF/DWARFDebugInfoTest.cpp
@@ -1122,26 +1122,57 @@ TEST(DWARFDebugInfo, TestRelations) {
   EXPECT_EQ(C1.getParent(), C);
   EXPECT_EQ(C2.getParent(), C);
 
-  // Make sure bidirectional iterator works as expected.
-  auto Begin = A.begin();
-  auto End = A.end();
-  auto It = A.begin();
-
-  EXPECT_EQ(It, Begin);
-  EXPECT_EQ(*It, B);
-  ++It;
-  EXPECT_EQ(*It, C);
-  ++It;
-  EXPECT_EQ(*It, D);
-  ++It;
-  EXPECT_EQ(It, End);
-  --It;
-  EXPECT_EQ(*It, D);
-  --It;
-  EXPECT_EQ(*It, C);
-  --It;
-  EXPECT_EQ(*It, B);
-  EXPECT_EQ(It, Begin);
+  // Make sure iterators work as expected.
+  EXPECT_THAT(std::vector<DWARFDie>(A.begin(), A.end()),
+              testing::ElementsAre(B, C, D));
+  EXPECT_THAT(std::vector<DWARFDie>(A.rbegin(), A.rend()),
+              testing::ElementsAre(D, C, B));
+
+  // Make sure iterator is bidirectional.
+  {
+    auto Begin = A.begin();
+    auto End = A.end();
+    auto It = A.begin();
+
+    EXPECT_EQ(It, Begin);
+    EXPECT_EQ(*It, B);
+    ++It;
+    EXPECT_EQ(*It, C);
+    ++It;
+    EXPECT_EQ(*It, D);
+    ++It;
+    EXPECT_EQ(It, End);
+    --It;
+    EXPECT_EQ(*It, D);
+    --It;
+    EXPECT_EQ(*It, C);
+    --It;
+    EXPECT_EQ(*It, B);
+    EXPECT_EQ(It, Begin);
+  }
+
+  // Make sure reverse iterator is bidirectional.
+  {
+    auto Begin = A.rbegin();
+    auto End = A.rend();
+    auto It = A.rbegin();
+
+    EXPECT_EQ(It, Begin);
+    EXPECT_EQ(*It, D);
+    ++It;
+    EXPECT_EQ(*It, C);
+    ++It;
+    EXPECT_EQ(*It, B);
+    ++It;
+    EXPECT_EQ(It, End);
+    --It;
+    EXPECT_EQ(*It, B);
+    --It;
+    EXPECT_EQ(*It, C);
+    --It;
+    EXPECT_EQ(*It, D);
+    EXPECT_EQ(It, Begin);
+  }
 }
 
 TEST(DWARFDebugInfo, TestDWARFDie) {
-- 
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