On Thu, 2015-08-13 at 02:14 -0700, Matthew Fortune wrote: > Hi Steve, > > Overall, I don't think these optimizations are ready to include. In principle > the idea looks good but it is done at the wrong point in the compiler in my > opinion. > > The biggest concern I have is that the analysis should be possible at (or > prior to) the point where the prologue/epilogue are expanded. I don't think > it is safe enough to post-process the code and delete the stack allocation.
I think that to do this, what we would have to do is introduce a new pass at the tree level (just before expanding to rtl) where we could do the analysis of whether or not the outgoing argument area is needed or not. Then we could use that info during expand_prologue to reset frame->args_size if the space is not needed. > There is at least one other optimization idea that competes with this one > which is to allow LRA to use the argument save area for arbitrary spills when > it is not used for spilling arguments or to prepare varargs. I think we need > to at least consider how the frame header removal will interact with such > an optimization. I am not sure how this would work. It seems better to just not allocate the space if it is not needed and then LRA can separately allocate whatever it needs for its own use (if any). I'll add Robert to the cc list on this in case he has any ideas since he did the LRA implementation for MIPS. Steve Ellcey sell...@imgtec.com
