[Bug 78468] Compiling of shader gets stuck in infinite loop

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=78468

Kenneth Graunke <kenneth at whitecape.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #19 from Kenneth Graunke <kenneth at whitecape.org> ---
(In reply to comment #18)
> This patch also fixes the game Dreadout for me on Intel.
> I have tested the patch successfully with mesa 10.2.7.
> Without this patch Dreadout gets stuck on start and shows only a black
> screen (not crashing).
> 
> Thank you Ken.
> Hope this patch lands in 10.2.8 and 10.3.0.

Awesome!  I'm glad to hear it.

It looks like Ian committed my patch, so marking this as fixed.  Emil will pick
up the patches for the new stable releases.

commit 84a40ce86b1010873b194eb9bf0b8744234b829c
Author: Kenneth Graunke <kenneth at whitecape.org>
Date:   Fri Sep 12 15:16:57 2014 -0700

    glsl: Speed up constant folding for swizzles.

    ir_rvalue::constant_expression_value() recursively walks down an IR
    tree, attempting to reduce it to a single constant value.  This is
    useful when you want to know whether a variable has a constant
    expression value at all, and if so, what it is.

    The constant folding optimization pass attempts to replace rvalues with
    their constant expression value from the bottom up.  That way, we can
    optimize subexpressions, and ideally stop as soon as we find a
    non-constant subexpression.

    In order to obtain the actual value of an expression, the optimization
    pass calls constant_expression_value().  But it should only do so if it
    knows the value can be combined into a constant.  Otherwise, at each
    step of walking back up the tree, it will walk down the tree again, only
    to discover what it already knew: it isn't constant.

    We properly avoided this call for ir_expression nodes, but not for
    ir_swizzle nodes.  This patch fixes that, drastically reducing compile
    times on certain shaders where tree grafting has given us huge
    expression trees.  It also fixes SuperTuxKart.

    Thanks to Iago and Mike for help in tracking this down.

    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=78468
    Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
    Reviewed-by: Jordan Justen <jordan.l.justen at intel.com>
    Reviewed-by: Ian Romanick <ian.d.romanick at intel.com>
    Cc: mesa-stable at lists.freedesktop.org

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