http://d.puremagic.com/issues/show_bug.cgi?id=2773
Don <[email protected]> changed: What |Removed |Added ---------------------------------------------------------------------------- Keywords| |patch --- Comment #8 from Don <[email protected]> 2009-10-06 00:17:14 PDT --- An even simpler test case shows something interesting: it happens only when there's an array assignment of 0, followed by another use of the same variable. An array assignment to 0 is an OPmemset operation in the backend. int* get() { return null; } void main(){ int* p = get(); p[0..3] = 0; // must be = 0!! Doesn't happen with any other number. p[0] = 7; } ANALYSIS: This is an OPmemset fight! In the optimisation loop, there's a localize step which rearranges the assignment, and there's a canonicalize step which sets it back the way it was before.... cgelem.c, elmemxxx() line 702 replaces ((e op= v) op e2) with ((e op=v), (e op e2)) ie, (p = get()), p) memset 0. ---> ((p = get()), p memset 0. glocal.c, local_exp() replaces p = get(); p memset 0; ---> (p = get(), p) memset 0 So it just keeps going round in circles. The fight can be broken up by changing cgelem.c elmemxxx() line 701 to avoid doing the first replacement: - if (e1->Eoper == OPcomma || OTassign(e1->Eoper)) + if (e1->Eoper == OPcomma) This probably isn't correct, there may be somewhere this particular canonicalisation is important. But without the DMC test suite, I can't tell. (Note that the comments in the code only refer to the OPcomma transformation, not the assignment one, so I presume the assignment was a later addition). -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
