charfi asma <charfiasma@xxxxxxxx> writes: > I would like to understand the gimplification step in GCC and I heard about unstructured and structured gimple produced from code (gcc summit 2005, gimplification improvment) > for example, to improve gimplification, Gimple code generated from. > > if (a++ +b != 0) return 0; else return 1; > should be : > D.1715 = a + b; > a = a + 1; > if (D.1715 != 0) goto <D.1716>; else goto <D.1717>; > > and this is not what gcc 4.4 produce (with interval.0...) > > I do not think that no body pays attentions to details generated in gimple. > I think that each introduced variable should be justified. I'm fairly sure that the 2005 paper is out of date with respect to current gcc. I suppose I would recommend that you examine the gcc source code to understand where these variables are coming from. That will give you an argument for whether the variable is justified or not. Don't lose sight of the fact that GIMPLE generation should be fast rather than optimal. The compiler already has to run a number of optimization passes which are completely able to remove unnecessary variables introduced during gimplification. If it takes time during gimplification to decide whether or not to introduce a variable, then it's better to introduce the variable and let the subsequent pass, which we know we are going to run anyway, clean it up. Of course, if the variable can be omitted during gimplification without taking any time, then that is better still. Ian
