From 78ce522932e8c356880c7ca10dace4b6fe6cf313 Mon Sep 17 00:00:00 2001 From: Eric Anholt Date: Fri, 30 Nov 2012 15:54:19 -0800 Subject: [PATCH] i965/fs: Add a note explaining a detail of register_coalesce_2(). Reviewed-by: Kenneth Graunke --- src/mesa/drivers/dri/i965/brw_fs.cpp | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp index 5d765e088aa..94d200eb5d4 100644 --- a/src/mesa/drivers/dri/i965/brw_fs.cpp +++ b/src/mesa/drivers/dri/i965/brw_fs.cpp @@ -1855,7 +1855,28 @@ fs_visitor::register_coalesce_2() } inst->remove(); + + /* We don't need to recalculate live intervals inside the loop despite + * flagging live_intervals_valid because we only use live intervals for + * the interferes test, and we must have had a situation where the + * intervals were: + * + * from to + * ^ + * | + * v + * ^ + * | + * v + * + * Some register R that might get coalesced with one of these two could + * only be referencing "to", otherwise "from"'s range would have been + * longer. R's range could also only start at the end of "to" or later, + * otherwise it will conflict with "to" when we try to coalesce "to" + * into Rw anyway. + */ live_intervals_valid = false; + progress = true; continue; } -- 2.30.2