[PATCH] D129825: Fix assertion in SmallDenseMap constructor with reserve from non-power-of-2 buckets count

[Afanasyev Ivan via Phabricator via llvm-commits]

ivafanas created this revision.
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`SmallDenseMap` constructor with reserve gets an arbitrary `NumInitBuckets` value and passes it below to `init` method.

If `NumInitBuckets` is greater then `InlineBuckets`, then `SmallDenseMap` initializes to large representation passing `NumInitBuckets` below to `DenseMap` initialization. `DenseMap::initEmpty` method asserts that initial buckets count must be a power of 2.

Proposed solution is to update `NumInitBuckets` value in `SmallDenseMap` constructor till the next power of 2. It should satisfy both `DenseMap` preconditions and required minimum buckets count for reservation.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D129825

Files:
  llvm/include/llvm/ADT/DenseMap.h
  llvm/unittests/ADT/DenseMapTest.cpp


Index: llvm/unittests/ADT/DenseMapTest.cpp
===================================================================
--- llvm/unittests/ADT/DenseMapTest.cpp
+++ llvm/unittests/ADT/DenseMapTest.cpp
@@ -607,6 +607,15 @@
   EXPECT_TRUE(map.find(0) == map.end());
 }
 
+TEST(DenseMapCustomTest, SmallDenseMapWithNumBucketsNonPowerOf2) {
+  // Is not power of 2.
+  const unsigned NumInitBuckets = 33;
+  // Power of 2 less then NumInitBuckets.
+  constexpr unsigned InlineBuckets = 4;
+  // Constructor should not trigger assert.
+  SmallDenseMap<int, int, InlineBuckets> map(NumInitBuckets);
+}
+
 TEST(DenseMapCustomTest, TryEmplaceTest) {
   DenseMap<int, std::unique_ptr<int>> Map;
   std::unique_ptr<int> P(new int(2));
Index: llvm/include/llvm/ADT/DenseMap.h
===================================================================
--- llvm/include/llvm/ADT/DenseMap.h
+++ llvm/include/llvm/ADT/DenseMap.h
@@ -907,6 +907,8 @@
 
 public:
   explicit SmallDenseMap(unsigned NumInitBuckets = 0) {
+    if (NumInitBuckets > InlineBuckets)
+      NumInitBuckets = NextPowerOf2(NumInitBuckets - 1);
     init(NumInitBuckets);
   }
 


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