Joe McDonnell created IMPALA-9762:
-------------------------------------
Summary: 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
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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