http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59371
--- Comment #10 from Maciej W. Rozycki <ma...@linux-mips.org> --- (In reply to Jakub Jelinek from comment #9) Jakub, The fix has corrected the evaluation of `i++' however it has regressed the evaluation of `i < c'. This is because in the loop `i' is only ever assigned values that are lower than or equal to the value of `c' and here the `int' type can represent all values representable with the `signed short' and `unsigned short' types. Specifically, assuming the properties of the MIPS target, where `int' is 32-bit wide and `short' is 16-bit wide, we have the following cases of the `c' input value here: 1. 0 -- the loop is not entered because `i' is preset to 0 and equals `c' right away. 2. [1,32767] -- `i' is incremented from 0 until it reaches the value of `c', at which point the loop terminates. 3. [32768,65535] -- `i' is incremented from 0 up to 32767, at which point it wraps around to -32768 and continues being incremented to 32767 again. And so on, and so on. It never reaches the value of `c' or any higher value and therefore the loop never terminates. Based on the above observations it is enough to check for `i == c' as the loop termination condition. So I think this is still a performance regression from the user's point of view even though I realise this may not necessarily be an optimisation GCC has been previously designed for. Therefore I'd prefer to keep the bug open until/unless we decide it's impractical to implement a code transformation that would restore previous performance. Maciej
