Hi, On Mon, 30 May 2011, Alexandre Oliva wrote:
> > 3. expand dominators before dominated blocks, so that DEFs of > > replaceable SSA names are expanded before their uses. Expand them > > when they're encountered, but not requiring a REG as a result. > > Save the RTL expression that results from the expansion for use in > > debug insns and at the non-debug use. > > This patch addresses some of the problems in 2, avoiding expanding code > out of order within a block, and (hopefully) ensuring that, expanding > dominators before dominatedblocks, DEFs are expanded before USEs. That isn't necessary. Replaceable SSA_NAMEs are defined in the same BB as their use, and hence they're expanded strictly before their use already right now. > There is a theoretical possibility that a USE may be expanded before a > DEF, depending on internal details of out-of-ssa, This can only happen with non-replaceable SSA_NAMEs and I thought you wish to deal only with replaceable. That said, I dislike approach 2 for the same worries you noted. And with the above I don't see why your approach (3) isn't workable without changes to the BB order, which should then be a really small patch. As SSA_NAMEs are (fairly) dense it might be better to simply use an array instead of a pointer_map for the SSA_NAME->rtx mapping. Ciao, Michael.
