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https://issues.apache.org/jira/browse/IMPALA-9762?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Joe McDonnell reassigned IMPALA-9762:
-------------------------------------
Assignee: Joe McDonnell
> Fix GCC7 compilation issue: shift-count-overflow in tuple-row-compare.cc
> ------------------------------------------------------------------------
>
> Key: IMPALA-9762
> URL: https://issues.apache.org/jira/browse/IMPALA-9762
> Project: IMPALA
> Issue Type: Bug
> Components: Backend
> Affects Versions: Impala 4.0
> Reporter: Joe McDonnell
> Assignee: Joe McDonnell
> Priority: Major
>
> GCC 7 compilation fails on tuple-row-compare.cc with the following:
>
> {noformat}
> /home/joe/view2/Impala/be/src/util/tuple-row-compare.cc: In instantiation of
> \u2018U impala::TupleRowZOrderComparator::GetSharedFloatRepresentation(void*,
> U) const [with U = unsigned int; T = double]\u2019:
> /home/joe/view2/Impala/be/src/util/tuple-row-compare.cc:405:53: required
> from \u2018U impala::TupleRowZOrderComparator::GetSharedRepresentation(void*,
> impala::ColumnType) const [with U = unsigned int]\u2019
> /home/joe/view2/Impala/be/src/util/tuple-row-compare.cc:357:41: required
> from \u2018int impala::TupleRowZOrderComparator::CompareBasedOnSize(const
> impala::TupleRow*, const impala::TupleRow*) const [with U = unsigned
> int]\u2019
> /home/joe/view2/Impala/be/src/util/tuple-row-compare.cc:343:49: required
> from here
> /home/joe/view2/Impala/be/src/util/tuple-row-compare.cc:454:33: error: left
> shift count >= width of type [-Werror=shift-count-overflow]
> return static_cast<U>(~tmp) << std::max((sizeof(U) - sizeof(T)) * 8,
> (uint64_t)0);
>
> ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> /home/joe/view2/Impala/be/src/util/tuple-row-compare.cc:457:33: error: left
> shift count >= width of type [-Werror=shift-count-overflow]
> return (static_cast<U>(tmp) << std::max((sizeof(U) - sizeof(T)) * 8,
> (uint64_t)0)) ^
>
> ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> cc1plus: all warnings being treated as errors
> {noformat}
>
> What is happening is that GCC is creating some template instantiations of
> TupleRowZOrderComparator::GetSharedRepresentation() and
> TupleRowZOrderComparator::CompareBasedOnSize(). The code at issue is doing
> this calculation:
>
> {code:java}
> return (static_cast<U>(val) <<
> std::max((sizeof(U) - sizeof(T)) * 8, (uint64_t)0)) ^ mask;
> {code}
>
> However, for these template instantiations, sizeof(T) > sizeof(U). That
> condition is impossible and never executed in Impala, but the instantiation
> exists. The compiler is intepreting the sizeof(U) - sizeof(T) not as a
> negative integer, but as a very very large positive integer (maybe due to the
> uint64_t 0). It wins the max calculation and triggers the
> shift-count-overflow.
> The fix is to do the max calculation with signed integers and then cast it to
> unsigned for the shift.
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