[llvm-branch-commits] [llvm] 260a856 - ADT: Fix reference invalidation in SmallVector::resize

[Duncan P. N. Exon Smith via llvm-branch-commits]

Author: Duncan P. N. Exon Smith
Date: 2021-01-13T20:48:08-08:00
New Revision: 260a856c2abcef49c7cb3bdcd999701db3e2af38

URL: https://github.com/llvm/llvm-project/commit/260a856c2abcef49c7cb3bdcd999701db3e2af38
DIFF: https://github.com/llvm/llvm-project/commit/260a856c2abcef49c7cb3bdcd999701db3e2af38.diff

LOG: ADT: Fix reference invalidation in SmallVector::resize

For small enough, trivially copyable `T`, take the parameter by-value in
`SmallVector::resize`.  Otherwise, when growing, update the arugment
appropriately.

Differential Revision: https://reviews.llvm.org/D93781

Added: 
    

Modified: 
    llvm/include/llvm/ADT/SmallVector.h
    llvm/unittests/ADT/SmallVectorTest.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/include/llvm/ADT/SmallVector.h b/llvm/include/llvm/ADT/SmallVector.h
index fea8a763d48f..ac445e556ba1 100644
--- a/llvm/include/llvm/ADT/SmallVector.h
+++ b/llvm/include/llvm/ADT/SmallVector.h
@@ -565,7 +565,7 @@ class SmallVectorImpl : public SmallVectorTemplateBase<T> {
   /// Like resize, but \ref T is POD, the new values won't be initialized.
   void resize_for_overwrite(size_type N) { resizeImpl<true>(N); }
 
-  void resize(size_type N, const T &NV) {
+  void resize(size_type N, ValueParamT NV) {
     if (N == this->size())
       return;
 
@@ -575,11 +575,8 @@ class SmallVectorImpl : public SmallVectorTemplateBase<T> {
       return;
     }
 
-    this->assertSafeToReferenceAfterResize(&NV, N);
-    if (this->capacity() < N)
-      this->grow(N);
-    std::uninitialized_fill(this->end(), this->begin() + N, NV);
-    this->set_size(N);
+    // N > this->size(). Defer to append.
+    this->append(N - this->size(), NV);
   }
 
   void reserve(size_type N) {

diff  --git a/llvm/unittests/ADT/SmallVectorTest.cpp b/llvm/unittests/ADT/SmallVectorTest.cpp
index c236a68636d0..1f6c7db99fa8 100644
--- a/llvm/unittests/ADT/SmallVectorTest.cpp
+++ b/llvm/unittests/ADT/SmallVectorTest.cpp
@@ -1135,12 +1135,14 @@ TYPED_TEST(SmallVectorReferenceInvalidationTest, Resize) {
   auto &V = this->V;
   (void)V;
   int N = this->NumBuiltinElts(V);
-#if !defined(NDEBUG) && GTEST_HAS_DEATH_TEST
-  EXPECT_DEATH(V.resize(N + 1, V.back()), this->AssertionMessage);
-#endif
+  V.resize(N + 1, V.back());
+  EXPECT_EQ(N, V.back());
 
-  // No assertion when shrinking, since the parameter isn't accessed.
-  V.resize(N - 1, V.back());
+  // Resize to add enough elements that V will grow again. If reference
+  // invalidation breaks in the future, sanitizers should be able to catch a
+  // use-after-free here.
+  V.resize(V.capacity() + 1, V.front());
+  EXPECT_EQ(1, V.back());
 }
 
 TYPED_TEST(SmallVectorReferenceInvalidationTest, Append) {