Zack Weinberg <[EMAIL PROTECTED]> writes: > Ian Lance Taylor <ian@airs.com> writes: > > > 3) Write a new CC0 collapse pass. This pass is run immediately > > after RTL expansion. It walks the instruction stream looking for > > instructions which set and use CC_REG. At this point these > > instructions will always be adjacent. The pass combines them into > > the combined instruction defined in step 2c above. > > 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. Ian
