[PATCH] D92717: [InstCombine] Fix miscompile into uadd.sat (PR48390)

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added a comment.

Please can you precommit the tests?
The fix looks like it just workarounds the problem, which is elsewhere.
Let me know if i should commandeer the revision.



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Comment at: llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp:766-786
   // Match unsigned saturated add of 2 variables with an unnecessary 'not'.
   // There are 8 commuted variants.
   // Canonicalize -1 (saturated result) to true value of the select. Just
   // swapping the compare operands is legal, because the selected value is the
   // same in case of equality, so we can interchange u< and u<=.
+  bool Swapped = false;
   if (match(FVal, m_AllOnes())) {
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Comment at: llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp:806-808
+  // The overflow may be detected via the add wrapping round. Which is only
+  // valid if we did not swap the true and false values.
+  if (!Swapped && match(Cmp0, m_c_Add(m_Specific(Cmp1), m_Value(Y))) &&
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Undo this


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https://reviews.llvm.org/D92717