[llvm] r361281 - [MergeICmps] Make sorting strongly stable on the rhs.

[Clement Courbet via llvm-commits]

Author: courbet
Date: Tue May 21 10:58:42 2019
New Revision: 361281

URL: http://llvm.org/viewvc/llvm-project?rev=361281&view=rev
Log:
[MergeICmps] Make sorting strongly stable on the rhs.

Summary:
Because the sort order was not strongly stable on the RHS, whether the
chain could merge would depend on the order of the blocks in the Phi.

EXPENSIVE_CHECKS would shuffle the blocks before sorting, resulting in
non-deterministic merging.

Reviewers: gchatelet

Subscribers: hiraditya, llvm-commits, RKSimon

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D62193

Modified:
    llvm/trunk/lib/Transforms/Scalar/MergeICmps.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/MergeICmps.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/MergeICmps.cpp?rev=361281&r1=361280&r2=361281&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/MergeICmps.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/MergeICmps.cpp Tue May 21 10:58:42 2019
@@ -507,7 +507,8 @@ BCECmpChain::BCECmpChain(const std::vect
   // semantics because we are only accessing dereferencable memory.
   llvm::sort(Comparisons_,
              [](const BCECmpBlock &LhsBlock, const BCECmpBlock &RhsBlock) {
-               return LhsBlock.Lhs() < RhsBlock.Lhs();
+               return std::tie(LhsBlock.Lhs(), LhsBlock.Rhs()) <
+                      std::tie(RhsBlock.Lhs(), RhsBlock.Rhs());
              });
 #ifdef MERGEICMPS_DOT_ON
   errs() << "AFTER REORDERING:\n\n";