[PATCH] D134805: [ADT] IntervalTree - Random unittests failures in a debug build

[Carlos Alberto Enciso via Phabricator via llvm-commits]

CarlosAlbertoEnciso created this revision.
CarlosAlbertoEnciso added reviewers: antondaubert, probinson, psamolysov, Orlando.
CarlosAlbertoEnciso added projects: All, LLVM.
Herald added a subscriber: mgrang.
CarlosAlbertoEnciso requested review of this revision.
Herald added a subscriber: llvm-commits.

As reported by @antondaubert:

On a debug build with _LIBCPP_DEBUG_RANDOMIZE_UNSPECIFIED_STABILITY enabled from 100 executions around 80 are failing.

More details in https://reviews.llvm.org/D125776#3820399

The issue is related to the use of `std::sort`.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D134805

Files:
  llvm/include/llvm/ADT/IntervalTree.h


Index: llvm/include/llvm/ADT/IntervalTree.h
===================================================================
--- llvm/include/llvm/ADT/IntervalTree.h
+++ llvm/include/llvm/ADT/IntervalTree.h
@@ -421,17 +421,17 @@
     // Sort intervals on the left and right of the middle point.
     if (NewBucketSize > 1) {
       // Sort the intervals in ascending order by their beginning point.
-      std::sort(IntervalsLeft.begin() + NewBucketStart,
-                IntervalsLeft.begin() + NewBucketStart + NewBucketSize,
-                [](const DataType *LHS, const DataType *RHS) {
-                  return LHS->left() < RHS->left();
-                });
+      std::stable_sort(IntervalsLeft.begin() + NewBucketStart,
+                       IntervalsLeft.begin() + NewBucketStart + NewBucketSize,
+                       [](const DataType *LHS, const DataType *RHS) {
+                         return LHS->left() < RHS->left();
+                       });
       // Sort the intervals in descending order by their ending point.
-      std::sort(IntervalsRight.begin() + NewBucketStart,
-                IntervalsRight.begin() + NewBucketStart + NewBucketSize,
-                [](const DataType *LHS, const DataType *RHS) {
-                  return LHS->right() > RHS->right();
-                });
+      std::stable_sort(IntervalsRight.begin() + NewBucketStart,
+                       IntervalsRight.begin() + NewBucketStart + NewBucketSize,
+                       [](const DataType *LHS, const DataType *RHS) {
+                         return LHS->right() > RHS->right();
+                       });
     }
 
     if (PointsBeginIndex <= MiddleIndex - 1) {
@@ -626,14 +626,14 @@
   /// Ascending: return the intervals with the smallest at the front.
   /// Descending: return the intervals with the biggest at the front.
   static void sortIntervals(IntervalReferences &IntervalSet, Sorting Sort) {
-    std::sort(IntervalSet.begin(), IntervalSet.end(),
-              [Sort](const DataType *RHS, const DataType *LHS) {
-                return Sort == Sorting::Ascending
-                           ? (LHS->right() - LHS->left()) >
-                                 (RHS->right() - RHS->left())
-                           : (LHS->right() - LHS->left()) <
-                                 (RHS->right() - RHS->left());
-              });
+    std::stable_sort(IntervalSet.begin(), IntervalSet.end(),
+                     [Sort](const DataType *RHS, const DataType *LHS) {
+                       return Sort == Sorting::Ascending
+                                  ? (LHS->right() - LHS->left()) >
+                                        (RHS->right() - RHS->left())
+                                  : (LHS->right() - LHS->left()) <
+                                        (RHS->right() - RHS->left());
+                     });
   }
 
   /// Print the interval tree.
@@ -654,7 +654,7 @@
       Points.push_back(Data.right());
       References.push_back(std::addressof(Data));
     }
-    std::sort(Points.begin(), Points.end());
+    std::stable_sort(Points.begin(), Points.end());
     auto Last = std::unique(Points.begin(), Points.end());
     Points.erase(Last, Points.end());
 


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