Suggestion for a fix to Bug middle-end/20177

[James E Wilson]

Mostafa Hagog wrote:
> Thanks for the information, what we were doing was to call
> update_life_info_in_dirty_blocks, but for some reason this wasn't
> sufficient to
> mark a register dead (REG_DEAD note) when the register was defined in a
> predecessor block and dies in the dirty block; we had to call
> update_life_info
> for all the blocks to mark that register as dead. Is there cases that we
> know
> about that such case could happen? is this means a bug in update_life_info

I am not sure I have enough info to answer this.

If you are moving instructions from one block to another, then you may 
need a full life pass, which means not using UPDATE_LIFE_LOCAL.  With 
UPDATE_LIFE_LOCAL, we assume that the info on which registers are live 
at the end of each block is still correct, and we just update info 
within blocks, i.e. making sure REG_DEAD notes within a block are in the 
right place, as this might have changed.  But if you need changes to 
global_live_at_{start,end} then you need to rerun a full life pass 
without UPDATE_LIFE_LOCAL to recompute this info.

Otherwise, I am not sure what the problem might be.  You might try 
spending a little time figuring out how update_life_info works.
-- 
Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com