------- Comment #8 from sandra at codesourcery dot com 2010-06-10 13:01 ------- I was barking up the wrong tree with my last idea -- the signed/unsigned conversion business was a red herring. Here's what I now believe is the problem: the costs computation is underestimating the register pressure costs so that we are in fact spilling when the cost computation thinks it still has "free" registers.
A hack to make get_computation_cost_at add target_reg_cost to the result when it must use a scratch register seemed to have positive overall effects on code size (as well as fixing the test case). But, I don't think that's the real solution, as I can't come up with a good logical justification for putting such a cost there. :-) estimate_reg_pressure_cost already reserves 3 "free" registers for such things. Anyway, I am continuing to poke at this in hopes of figuring out where the register costs model is really going wrong. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42505
