Re: [PATCH]: Implement must-def kill operand

[Daniel Berlin <dberlin at dberlin dot org>]

On Oct 20, 2004, at 4:32 PM, Diego Novillo wrote:

> On Wed, 2004-10-20 at 14:20, Daniel Berlin wrote:
>
> > 1. Do a quick propagation pass in DCE to make sure def-def phis that
> > are used in necessary statements don't die. (at that point, plain
> > def-def renaming will work)
> > 2. Mark the must-def operand as necessary if it's a phi, and the only
> > immediate use of the phi is in the must-def operand (I'm assuming it
> > could appear in a may-def or vuse somewhere else, in which case it's
> > necessary).
> > 3. Use the full renamer, which will simply put the phi back after DCE
> > removes it.
> 4. If the RHS of a V_MUST_DEF is a PHI node, mark it necessary?

That's #1, actually.

Before remove_stmts, i meant you do this:

FOR EACH MUSTDEF:
If RHS is a phi node and marked unnecessary:
	add phi node to worklist.


Until worklist is empty:
	pop phi off worklist. Mark as necessary.
	For each phi node argument that is a phi node marked unnecessary, add 
to worklist.

This also catches the mutually recursive phis like:
a_1 = phi <a_2, <a_something>>
a_2 = phi <a_4, a_1>

a_4 = must_def <a_2>

You actually have to worklist it because those phi nodes may use phi 
nodes, and you have to mark those phi nodes as necessary as well.
:)

> Diego.