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Re: PR 23551: why should we coalesce inlined variables?

On 7/8/07, Daniel Berlin <> wrote:
On 7/8/07, Alexandre Oliva <> wrote:
> On Jul  7, 2007, Jan Hubicka <> wrote:
> >> On Jun 28, 2007, Andrew MacLeod <> wrote:
> >>

> That said, maybe with the work I have in mind we'll be able to enable
> coalescing for all user variables (not only those coming from inlined
> functions), and retain the annotations needed to map the assignments
> back to user variables somehow.  However, I'm not convinced yet that
> it can be done in a way that consumes less memory, basically because
> we'd have to keep track of which variables map to which assignments to
> SSA variables, and this would amount to further SSA analysis and
> assignments, or annotations that would have to be dealt with in a very
> similar way.  That said, ideas are welcome.

This looks like a standard propagation problem you could use
tree-ssa-propagate to solve, generate the mapping, output debugging
info, and throw away the mapping.

The problem is that this is a N:M mapping and that we lose parts of the N during optimization and especially inlining. The "goal" is to know every user variable name that a current register refers to. So we need to keep track of any variable that is propagated into a register at any time, even if we later manage to get rid of the variable because it is unused.


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