[Octave-bug-tracker] [bug #62212] Wrong unsigned integer overflow with clang

[Markus Mützel]

Follow-up Comment #4, bug #62212 (project octave):

Hmm..
g++ only gets this exactly right when compiling without optimization (which
might be the default on Ubuntu?):

$ g++ -O0 -otest_cast test_cast.cc
$ ./test_cast
db_large_integer: 1.84467e+19
ui64_large_integer: 0
$ g++ -O1 -otest_cast test_cast.cc
$ ./test_cast
db_large_integer: 1.84467e+19
ui64_large_integer: 18446744073709551615


... and the same for `-O2` and `-O3`. Maybe the default optimization level is
different for your system.
Do we compile Octave with `-O0`?

clang++ gets it always wrong (but differently depending on optimization
level):

$ clang++ -O0 -otest_cast test_cast.cc
$ ./test_cast
db_large_integer: 1.84467e+19
ui64_large_integer: 9223372036854775808
$ clang++ -O1 -otest_cast test_cast.cc
$ ./test_cast
db_large_integer: 1.84467e+19
ui64_large_integer: 4202531


... and the same for `-O2` and `-O3`.
All of those are too far off for the test case.

I wonder if there are tricks to avoid optimizations here or use different code
paths when the compiler generates code.



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