http://llvm.org/bugs/show_bug.cgi?id=12687
Bug #: 12687
Summary: clang should warn when tautologically comparing a
smaller-type numeric value against a larger-typed
constant outside the smaller type's range
Product: clang
Version: unspecified
Platform: All
OS/Version: All
Status: NEW
Severity: enhancement
Priority: P
Component: Frontend
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
Classification: Unclassified
I recently wrote code that looked roughly like this (the isfinite and copysign
expressions were spelled in other terms that didn't make the code look so
obviously wrong):
#include <math.h>
#include <stdlib.h>
inline double TimeClip(double time)
{
if (!isfinite(time) || abs(time) > 8.64e15)
return NAN;
return copysign(floor(fabs(time)), time + 0.0);
}
int main()
{
TimeClip(17.0);
return 0;
}
This code's buggy in that it uses abs (int -> int) when it should have used
fabs (double -> double). The compiler can't be expected to figure that out, of
course. But it should be able to figure out that no |int| value will ever be
greater than 8.64e15, and it should emit a tautological-compare warning just as
it would if it saw any other always-true or always-false comparison.
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