Mesa (main): intel/nir: Fix txs for null surfaces

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Module: Mesa
Branch: main
Commit: 4c67924251292106963afa4f27639fe5d3c32eef
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=4c67924251292106963afa4f27639fe5d3c32eef

Author: Iván Briano <ivan.briano at intel.com>
Date:   Wed Jun 16 15:49:25 2021 -0700

intel/nir: Fix txs for null surfaces

Closes: #4860
Fixes: 05a37e24220 ("intel/nir: Set lower txs with non-zero LOD")

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11435>

---

 src/compiler/nir/nir_lower_tex.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/src/compiler/nir/nir_lower_tex.c b/src/compiler/nir/nir_lower_tex.c
index e96676c2ffa..cf8275c5786 100644
--- a/src/compiler/nir/nir_lower_tex.c
+++ b/src/compiler/nir/nir_lower_tex.c
@@ -1127,10 +1127,14 @@ nir_lower_txs_lod(nir_builder *b, nir_tex_instr *tex)
    nir_instr_rewrite_src(&tex->instr, &tex->src[lod_idx].src,
                          nir_src_for_ssa(nir_imm_int(b, 0)));
 
-   /* TXS(LOD) = max(TXS(0) >> LOD, 1) */
+   /* TXS(LOD) = max(TXS(0) >> LOD, 1)
+    * But we do min(TXS(0), TXS(LOD)) to catch the case of a null surface,
+    * which should return 0, not 1.
+    */
    b->cursor = nir_after_instr(&tex->instr);
-   nir_ssa_def *minified = nir_imax(b, nir_ushr(b, &tex->dest.ssa, lod),
-                                    nir_imm_int(b, 1));
+   nir_ssa_def *minified = nir_imin(b, &tex->dest.ssa,
+                                    nir_imax(b, nir_ushr(b, &tex->dest.ssa, lod),
+                                             nir_imm_int(b, 1)));
 
    /* Make sure the component encoding the array size (if any) is not
     * minified.