Ian Lance Taylor <ian@airs.com> writes: > Zack Weinberg <[EMAIL PROTECTED]> writes: >> I'm not understanding why this is a separate pass, instead of >> generating the combined instructions directly in the expander. I >> think generic expander support for compare-and-branch instructions >> already exists... > > We have to worry not just about compare-and-branch, but also about > test-and-branch, compare-and-set, compare-and-move, and > compare-and-add. Basically, look for the various calls to > emit_cmp_insn. We could modify the expander to try combined > instructions in all those cases. Or we could modify the cc0 > backends to save the comparison operands in cmpMODE and use them in > the various conditional instructions (that was my original > proposal). Overall it seems simpler to use a separate pass. I'm > not wedded to it, though.
I kinda like the idea of having the cc0 backends save the comparison operands. That is, after all, what most of the non-cc0 backends do. It is not the way that I think things *should* work, but it does reduce the number of ways that things are done. (Long term, I *would* like to see named optabs for all of the above as fused operations, ideally as the only way the expander works.) zw
