https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80932
Bug ID: 80932
Summary: UBSAN: false positive as a result of distribution:
c1*(c2*v1-c3*v2)=>c1*c2*v1-c1*c3*v2
Product: gcc
Version: 8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: sanitizer
Assignee: unassigned at gcc dot gnu.org
Reporter: babokin at gmail dot com
CC: dodji at gcc dot gnu.org, dvyukov at gcc dot gnu.org,
jakub at gcc dot gnu.org, kcc at gcc dot gnu.org, marxin at
gcc dot gnu.org
Target Milestone: ---
gcc trunk rev248580, x86_64.
Transformation causing troubles: const1 * (const2 * var1 - const3 * var2) =>
const1*const2*var1 - const3*var2;
> cat f.cpp
#include <iostream>
signed char var_10 = 77;
long long int var_13 = 1547580415367384384LL;
long foo() {
long a = -6 *
// 0xbf8a6c24aa342bc0 = -4644781160949077056
(long(16636733186465668563ULL * var_13 ) -
// 0xd4cdd0f8c2df13cf = -3112602000603278385
long(678280911954875019ULL * var_10));
return a;
}
int main () {
long a = foo ();
std::cout << a << std::endl;
return 0;
}
> g++ -fsanitize=undefined -O0 f.cpp; ./a.out
f.cpp:6:8: runtime error: signed integer overflow: -9024801181724640896 -
228867929910118694 cannot be represented in type 'long int'
9193074962074792026
