Mesa (main): nir/lower_fragcolor: Avoid redundant load_output

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Module: Mesa
Branch: main
Commit: 95bd6e915f6bd14b45a341b3e0d3b62389ddd5de
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=95bd6e915f6bd14b45a341b3e0d3b62389ddd5de

Author: Alyssa Rosenzweig <alyssa at collabora.com>
Date:   Mon Jun  7 13:59:26 2021 -0400

nir/lower_fragcolor: Avoid redundant load_output

At best, this is an extra instruction for NIR to optimize out. At worst,
depending on pass ordering nir_load_output could sneak into the final
NIR, even on drivers that don't support fbfetch.

Signed-off-by: Alyssa Rosenzweig <alyssa at collabora.com>
Reviewed-by: Mike Blumenkrantz <michael.blumenkrantz at gmail.com>
Reviewed-by: Jason Ekstrand <jason at jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11255>

---

 src/compiler/nir/nir_lower_fragcolor.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/compiler/nir/nir_lower_fragcolor.c b/src/compiler/nir/nir_lower_fragcolor.c
index 15480361764..8c7c234efaa 100644
--- a/src/compiler/nir/nir_lower_fragcolor.c
+++ b/src/compiler/nir/nir_lower_fragcolor.c
@@ -65,7 +65,8 @@ lower_fragcolor_instr(nir_builder *b, nir_instr *intr, void *data)
       return false;
    b->cursor = nir_after_instr(&instr->instr);
 
-   nir_ssa_def *frag_color = nir_load_var(b, out);
+   assert(instr->src[1].is_ssa);
+   nir_ssa_def *frag_color = instr->src[1].ssa;
    ralloc_free(out->name);
 
    const char *name = out->data.index == 0 ? "gl_FragData[0]" :