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Previously the check was done as
unsigned int a, b, c;
c = a * b;
if (c < a)
// error
but it is wrong, since it catches only a subset of all the
possible overflows.
This patch improves the check as
unsigned int a, b, c;
if ((a > 1) && (b > 1){
if ((UINT_MAX/a) < b)
// error
}
An additional case has been added to the tests, with two 32-bit
values that cause overflow and are not detected by the old check.
It is also necessary to break the lowering procedure in case the current
BasicBlock is splitted; in this case it was necessary in order not to
trigger the division by 0 error.
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