On Tue, 2015-08-18 at 09:23 +0930, Alan Modra wrote: > On Mon, Aug 17, 2015 at 10:38:22AM -0700, Steve Ellcey wrote:
> OK, then you need to emit a .cfi directive to say the frame top is > given by the temp hard reg sometime after that assignment and before > sp is aligned in the prologue, and another .cfi directive when copying > to the pseudo. It's a while since I looked at the CFI code in gcc, > but arranging this might be as simple as setting RTX_FRAME_RELATED_P > on the insns involved. > > If -fasynchronous-unwind-tables, then you'll also need to track the > frame in the epilogue. > > > This function (fn2) ends with a call to abort, which is noreturn, so the > > optimizer sees that the epilogue is dead code and GCC determines that > > there is no need to save the old stack pointer since it will never get > > restored. I guess I need to tell GCC to save the stack pointer in > > expand_prologue even if it never sees a use for it. I guess I need to > > make the temporary register where I save $sp volatile or do something > > else so that the assignment (and its associated .cfi) is not deleted by > > the optimizer. > > Ah, I see. Yes, the temp and pseudo are not really dead if they are > needed for unwinding. Yes, I was originally thinking I just had to make the temp and pseudo regs volatile so that the assignments would not get removed but it appears that I need the epilogue code too (even if I never get there because of a call to abort which GCC knows is non-returning) so that I have the needed .cfi directives there. I am thinking I should add an edge from the entry_block to the exit_block so that the exit block is never removed by the optimizer. I assume this edge would need to be abnormal and/or fake but I am not sure which (if either) of these edges would be appropriate for this. Steve Ellcey sell...@imgtec.com
