Mesa (master): gallium/ntt: Work around virglrenderer UIF handling bug.

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Module: Mesa
Branch: master
Commit: 111e4be698a1940b05c1a9d0d8b269b96be75e1d
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=111e4be698a1940b05c1a9d0d8b269b96be75e1d

Author: Eric Anholt <eric at anholt.net>
Date:   Wed Jan  6 16:05:59 2021 -0800

gallium/ntt: Work around virglrenderer UIF handling bug.

Until just recently ("vrend: Fix TGSI UIF/IF behavior"), virgl does "if
(any(bvec4(src0)))" instead of "if (src0.x != 0)", despite the tgsi.rst
documentation and tgsi_exec agreeing on the second form.  It's harmless to
work around it, since apparently NTT was the only one to not have scalar
swizzled the if condition.

Reviewed-by: Gert Wollny <gert.wollny at collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8373>

---

 src/gallium/auxiliary/nir/nir_to_tgsi.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/gallium/auxiliary/nir/nir_to_tgsi.c b/src/gallium/auxiliary/nir/nir_to_tgsi.c
index 414bac858a2..88ba7d4bec2 100644
--- a/src/gallium/auxiliary/nir/nir_to_tgsi.c
+++ b/src/gallium/auxiliary/nir/nir_to_tgsi.c
@@ -2137,10 +2137,13 @@ ntt_emit_block(struct ntt_compile *c, nir_block *block)
    /* Set up the if condition for ntt_emit_if(), which we have to do before
     * freeing up the temps (the "if" is treated as inside the block for liveness
     * purposes, despite not being an instruction)
+    *
+    * Note that, while IF and UIF are supposed to look at only .x, virglrenderer
+    * looks at all of .xyzw.  No harm in working around the bug.
     */
    nir_if *nif = nir_block_get_following_if(block);
    if (nif)
-      c->if_cond = ntt_get_src(c, nif->condition);
+      c->if_cond = ureg_scalar(ntt_get_src(c, nif->condition), TGSI_SWIZZLE_X);
 
    /* Free up any SSA temps that are unused at the end of the block. */
    unsigned index;