[PATCH] D38197: [DebugInfo] Sort the SDDbgValue list before assuming it is in IR order

[Reid Kleckner via Phabricator via llvm-commits]

rnk marked an inline comment as done.
rnk added a comment.

Thanks!



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Comment at: llvm/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp:860
     // Sort the source order instructions and use the order to insert debug
     // values.
+    std::stable_sort(Orders.begin(), Orders.end(), less_first());
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aprantl wrote:
> Add a comment why the stable_sort is necessary?
I don't have a testcase to demonstrate any issue, but it will ensure that clang has the same output on all platforms regardless of the (usually deterministic) instability in sort order. Anyways, commented.


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Comment at: llvm/test/DebugInfo/X86/dbg-value-transfer-order.ll:27-39
+; CHECK .LBB0_1:                                # %while.body
+; CHECK         movl    $32, %ecx
+; CHECK         testl   {{.*}}
+; CHECK         jne     .LBB0_3
+; CHECK # BB#2:                                 # %if.then
+; CHECK         callq   if_then
+; CHECK         movl    %eax, %ecx
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Ka-Ka wrote:
> I had problem recreating the fault as this testcase passed both with or without your changes in ScheduleDAGSDNodes.cpp, but then I realized that the checks in these lines don't check anything as they are missing a ':' after the CHECK.
> 
Oops. I added the colons and confirmed that the test fails without the sort. Without the fix, the DBG_VALUE for bit_offset appears at the end of `.LBB0_3`.


https://reviews.llvm.org/D38197