LIMITS.cpp WCHAR test causes infinite loop with IPA, nonstandard code
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Key: STDCXX-264
URL: http://issues.apache.org/jira/browse/STDCXX-264
Project: C++ Standard Library
Issue Type: Bug
Components: Configuration
Affects Versions: 4.1.3
Environment: > uname -a && CC -V
UNICOS/mp sn702 3.0.62 07230830 crayx1
Cray C++ : Version 5.6.0.0.57 Mon Jul 31, 2006 14:38:56
Reporter: Colin Lee
Priority: Minor
With any compiler that uses interprocedural analysis including leaf node
inlining, this WCHAR test in etc/config/src/LIMITS.cpp invokes undefined
behavior from signed integer overflow and can result in an infinite loop. Our
compiler inlines the greater() function and invokes undefined behavior, so the
loop never exits. One workaround is to disable optimization and run the code
by hand, but since this code is hidden within the build process, a portable
solution is needed. Here's a code snippet:
template <class T>
T greater (T lhs, T rhs)
{
// prevents overzealous gcc optimizer from invoking
// undefined behavior on signed integer over/underflow
return lhs > rhs;
}
template <class T>
T compute_limits (T, const char *pfx, const char *sfx, const char *type)
{
T max = T (1);
T one = T (1);
for (; T (max * 2) > max; max *= 2);
for (T n = max / 4; n; ) {
if (T (max + n) < max) {
if (n > 2)
n /= 2;
else if (greater (T (max + one), max))
n = 1;
else
break;
}
else
max += n;
}
return max;
}
int main(void) {
compute_limits ((wchar_t)0, "WCHAR_T", suffix, "wchar_t");
return 0;
}
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