ADT: Weaken SmallVector::resize assertion from 5abf76fbe37380874a88cc9aa02164800e4e10f3

[dexonsmith]

Summary

There's no need to check for reference invalidation when
SmallVector::resize is shrinking; the parameter isn't accessed.

[dexonsmith]

Thanks for the review! Committed in 40e877264dc5bd9a025bc1fc0f01fb69a3f3cdc2.

llvm/include/llvm/ADT/SmallVector.h

if (N < this->size()) {
         this->grow(N);
       for (auto I = this->end(), E = this->begin() + N; I != E; ++I)
         new (&*I) T();
       this->set_size(N);
     }
   }
 
   void resize(size_type N, const T &NV) {
-    this->assertSafeToReferenceAfterResize(&NV, N);
     if (N < this->size()) {
       this->destroy_range(this->begin()+N, this->end());
       this->set_size(N);
     } else if (N > this->size()) {
+      this->assertSafeToReferenceAfterResize(&NV, N);
       if (this->capacity() < N)
         this->grow(N);
       std::uninitialized_fill(this->end(), this->begin()+N, NV);
       this->set_size(N);
     }
   }
 
   void reserve(size_type N) {

llvm/unittests/ADT/SmallVectorTest.cpp

 #if !defined(NDEBUG) && GTEST_HAS_DEATH_TEST
   EXPECT_DEATH(V.push_back(std::move(V.back())), this->AssertionMessage);
 #endif
 }
 
 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(2, V.back()), this->AssertionMessage);
+  EXPECT_DEATH(V.resize(N + 1, V.back()), this->AssertionMessage);
 #endif
+
+  // No assertion when shrinking, since the parameter isn't accessed.
+  V.resize(N - 1, V.back());
 }
 
 TYPED_TEST(SmallVectorReferenceInvalidationTest, Append) {
   auto &V = this->V;
   (void)V;
 #if !defined(NDEBUG) && GTEST_HAS_DEATH_TEST
   EXPECT_DEATH(V.append(1, V.back()), this->AssertionMessage);
 #endif