[PATCH] D99544: [VPlan] Use SmallVector for VPExternalDefs to prevent non-determinism.

[Huihui Zhang via Phabricator via llvm-commits]

huihuiz created this revision.
huihuiz added reviewers: efriedma, StephenTozer, MaskRay, nikic, zzheng, mgrang.
huihuiz added a project: LLVM.
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Use SmallVector instead of SmallPtrSet for external definitions created
for VPlan. Doing this can help avoid non-determinism caused by iterating
over unordered containers.

This bug was found with reverse iteration turning on,
 --extra-llvm-cmake-variables="-DLLVM_REVERSE_ITERATION=ON".
Failing LLVM-Unit test VPRecipeTest.dump.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D99544

Files:
  llvm/lib/Transforms/Vectorize/VPlan.h


Index: llvm/lib/Transforms/Vectorize/VPlan.h
===================================================================
--- llvm/lib/Transforms/Vectorize/VPlan.h
+++ llvm/lib/Transforms/Vectorize/VPlan.h
@@ -1767,7 +1767,7 @@
   // VPlan. External definitions must be immutable and hold a pointer to its
   // underlying IR that will be used to implement its structural comparison
   // (operators '==' and '<').
-  SmallPtrSet<VPValue *, 16> VPExternalDefs;
+  SmallVector<VPValue *, 16> VPExternalDefs;
 
   /// Represents the backedge taken count of the original loop, for folding
   /// the tail.
@@ -1835,9 +1835,7 @@
 
   /// Add \p VPVal to the pool of external definitions if it's not already
   /// in the pool.
-  void addExternalDef(VPValue *VPVal) {
-    VPExternalDefs.insert(VPVal);
-  }
+  void addExternalDef(VPValue *VPVal) { VPExternalDefs.push_back(VPVal); }
 
   void addVPValue(Value *V) {
     assert(V && "Trying to add a null Value to VPlan");


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