[Mesa-dev] [PATCH 1/4] glsl: Teach ir_variable_refcount about ir_loop::counter variables.

[Eric Anholt]

Paul Berry <stereotype441 at gmail.com> writes:

> If an ir_loop has a non-null "counter" field, the variable referred to
> by this field is implicitly read and written by the loop.  We need to
> account for this in ir_variable_refcount, otherwise there is a danger
> we will try to dead-code-eliminate the loop counter variable.
>
> Note: at the moment the dead code elimination bug doesn't occur due to
> a bug in ir_hierarchical_visitor: it doesn't visit the "counter"
> field, so dead code elimination doesn't treat it as a candidate for
> elimination.  But the patch to follow will fix that bug, so we need to
> fix ir_variable_refcount first in order to avoid breaking dead code
> elimination.

This series is:

Reviewed-by: Eric Anholt <eric at anholt.net>

I wish loop_control.cpp would make loop->control informational, and not
muck with the existing control flow in the loop.  That way we could just
ignore loop->control in the backend, and it would only get used by loop
unrolling.  I'm pretty sure I've seen loops where both loop controls
(loop->control and the original variable) end up getting used, and it's
something that's going to be hard for the backend to fix back up.
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