Vincent Lefevre <vincent+gcc@xxxxxxxxxx> writes: > On 2008-12-01 13:02:21 -0800, Ian Lance Taylor wrote: >> "Nirav Shah" <nirav4ever4u@xxxxxxxxx> writes: >> >> > No expression is evaluated in loop nor any particular intermediate >> > result is used more than once. Given this, can I get benefit in terms >> > of lesser clock cycle to execute the computation if done in a single >> > statement as compared to done over multiple statements with local >> > variables? >> >> No. When optimizing, the compiler converts your program into an >> internal representation in SSA form. The number of local variables >> used in the original program is irrelevant to the generated code. > > This may be what GCC currently does, but this is a bug when extended > precision is used to evaluate an expression. > > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=323 Yes. By default, using additional local variables does not affect that bug in any meaningful way. However, you are correct in that if you use the -ffloat-store option gcc will essentially treat all local variables with floating point type as though they were declared with the volatile qualifier. That is indeed a case where it matters whether or not you use local variables. By the way, that long-standing bug will likely be fixed in gcc 4.5 (i.e., not the next release, which will be 4.4, but the one after that). Ian
