Matthew D. Fuller wrote:
Important to note is that this only happens when compiling with
optimization (they claim).
% cc -o test test.c
% ./test
X
% cc -O -o test test.c
% ./test
X
% cc -O2 -o test test.c
% ./test
%
gcc version 4.2.1 20070719 [FreeBSD]
I can confirm this on ubuntu:
gcc 4.1 w/o optimization:
no overflow (= fail)
gcc 4.1 w/o opt && -fwrapv:
overflow (= good)
gcc 4.2 w/o opt:
overflow
gcc 4.2 w/ opt:
no overflow
gcc 4.2 w/ opt && -fwrapv:
overflow
So no matter whether we upgrade gcc or not, we should change the default
optimization to behave as if -fwrapv was passed. Or we emit warnings whenever
this optimization is taking place. Or both :)
cheers
simon
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