Re: How do I modify SSA and copy basic blocks?

[Jeff Law <law at redhat dot com>]

On 04/23/2013 02:43 PM, Steve Ellcey wrote:
> I think I have code that finds the path that I am interested in, but when
> I try to use copy_bbs to copy the basic blocks in order to create my new path,
> I get segfaults.  I was wondering if anyone could help me understand what I
> need to do, in addition to calling copy_bbs, to create my new path and keep
> the various ssa and cfg information up to date, either by modifying it or by
> blowing it away and regenerating it, I am not worried about compilation speed
> at this point so if regenerating all the SSA/cfg data is easiest, I am happy
> to do that.
Well, you have to copy the blocks, adjust the edges and rewrite the SSA 
graph.  I'd use duplicate_block to help.

You really want to look at tree-ssa-threadupdate.c.  There's a nice big 
block comment which gives the high level view of what needs to happen 
when you copy a block for this kind of optimization.  Feel free to 
ignore the implementation which has to be fairly efficient when there's 
a large number of edges to update.

Jeff