[llvm] e72209d - [MachineSink] Fix stable sort comparator (#116705)

[via llvm-commits]

Author: Ellis Hoag
Date: 2024-11-19T16:15:35-08:00
New Revision: e72209db3586ee03f433fe30c3bfac6c9c4d9d6f

URL: https://github.com/llvm/llvm-project/commit/e72209db3586ee03f433fe30c3bfac6c9c4d9d6f
DIFF: https://github.com/llvm/llvm-project/commit/e72209db3586ee03f433fe30c3bfac6c9c4d9d6f.diff

LOG: [MachineSink] Fix stable sort comparator (#116705)

Fix the comparator in `stable_sort()` to satisfy the strict weak
ordering requirement.

In https://github.com/llvm/llvm-project/pull/115367 this comparator was
changed to use `getCycleDepth()` when `shouldOptimizeForSize()` is true.
However, I mistakenly changed to logic so that we use `LHSFreq <
RHSFreq` if **either** of them are zero. This causes us to fail the last
requirment (https://en.cppreference.com/w/cpp/named_req/Compare).

> if comp(a, b) == true and comp(b, c) == true then comp(a, c) == true

Added: 
    

Modified: 
    llvm/lib/CodeGen/MachineSink.cpp

Removed: 
    


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diff  --git a/llvm/lib/CodeGen/MachineSink.cpp b/llvm/lib/CodeGen/MachineSink.cpp
index c470bd71dfb29f..0def107f6306d7 100644
--- a/llvm/lib/CodeGen/MachineSink.cpp
+++ b/llvm/lib/CodeGen/MachineSink.cpp
@@ -1227,7 +1227,8 @@ MachineSinking::GetAllSortedSuccessors(MachineInstr &MI, MachineBasicBlock *MBB,
       AllSuccs, [&](const MachineBasicBlock *L, const MachineBasicBlock *R) {
         uint64_t LHSFreq = MBFI ? MBFI->getBlockFreq(L).getFrequency() : 0;
         uint64_t RHSFreq = MBFI ? MBFI->getBlockFreq(R).getFrequency() : 0;
-        if (llvm::shouldOptimizeForSize(MBB, PSI, MBFI) || !LHSFreq || !RHSFreq)
+        if (llvm::shouldOptimizeForSize(MBB, PSI, MBFI) ||
+            (!LHSFreq && !RHSFreq))
           return CI->getCycleDepth(L) < CI->getCycleDepth(R);
         return LHSFreq < RHSFreq;
       });