<p dir="ltr">Reviewed-by: Chris Forbes <<a href="mailto:chrisf@ijw.co.nz">chrisf@ijw.co.nz</a>></p>
<div class="gmail_quote">On Aug 17, 2014 10:14 AM, "Kenneth Graunke" <<a href="mailto:kenneth@whitecape.org">kenneth@whitecape.org</a>> wrote:<br type="attribution"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
The optimization relies on CMP setting the destination to 0, which is<br>
equivalent to 0.0f. However, early platforms only set the least<br>
significant byte, leaving the other bits undefined. So, we must disable<br>
the optimization on those platforms.<br>
<br>
Oddly, Sandybridge wasn't reported as broken, even though it's<br>
documented to only set the LSB. It's unclear whether it follows ILK on<br>
IVB behavior.<br>
<br>
+32 piglits on Ironlake.<br>
<br>
Bugzilla: <a href="https://bugs.freedesktop.org/show_bug.cgi?=79963" target="_blank">https://bugs.freedesktop.org/show_bug.cgi?=79963</a><br>
Signed-off-by: Kenneth Graunke <<a href="mailto:kenneth@whitecape.org">kenneth@whitecape.org</a>><br>
---<br>
src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp | 7 +++++++<br>
1 file changed, 7 insertions(+)<br>
<br>
diff --git a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp<br>
index f22d38d..33cb9a9 100644<br>
--- a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp<br>
+++ b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp<br>
@@ -1135,6 +1135,13 @@ vec4_visitor::try_emit_mad(ir_expression *ir)<br>
bool<br>
vec4_visitor::try_emit_b2f_of_compare(ir_expression *ir)<br>
{<br>
+ /* This optimization relies on CMP setting the destination to 0 when<br>
+ * false. Early hardware only sets the least significant bit, and<br>
+ * leaves the other bits undefined. So we can't use it.<br>
+ */<br>
+ if (brw->gen < 7)<br>
+ return false;<br>
+<br>
ir_expression *const cmp = ir->operands[0]->as_expression();<br>
<br>
if (cmp == NULL)<br>
--<br>
1.9.2<br>
<br>
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</blockquote></div>