Mesa (main): r600: Fix reading back from a temp array immediately after writing on RV770.

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Module: Mesa
Branch: main
Commit: 25836895f3d57dbfd4d13572c4bb8f2ea5938408
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=25836895f3d57dbfd4d13572c4bb8f2ea5938408

Author: Emma Anholt <emma at anholt.net>
Date:   Sat Apr  2 22:19:59 2022 -0700

r600: Fix reading back from a temp array immediately after writing on RV770.

KHR-GL33.shaders.indexing.tmp_array.vertexid regressed with the switch to
NIR-to-TGSI because the shader got optimized enough to emit a read just
after writing to the array (the kind of situation where a non-rel write
would have been followed by a PV/PS read).  The R600 and EG docs say you
always need to do this, but apparently some hardware gives you the right
answer anyway so we don't flag it on all of them.

Reviewed-by: Gert Wollny <gert.wollny at collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14319>

---

 src/gallium/drivers/r600/r600_asm.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/src/gallium/drivers/r600/r600_asm.c b/src/gallium/drivers/r600/r600_asm.c
index 83bdfc75051..ec772d48dc1 100644
--- a/src/gallium/drivers/r600/r600_asm.c
+++ b/src/gallium/drivers/r600/r600_asm.c
@@ -148,6 +148,17 @@ void r600_bytecode_init(struct r600_bytecode *bc,
 	if ((chip_class == R600) &&
 	    (family != CHIP_RV670 && family != CHIP_RS780 && family != CHIP_RS880)) {
 		bc->ar_handling = AR_HANDLE_RV6XX;
+
+		/* Insert a nop after a relative temp write so that a read in
+		 * the following instruction group gets the right value.  The
+		 * r600 and EG ISA specs both say that read-after-rel-write of a
+		 * register in the next instr group is illegal, but apparently
+		 * that's not true on all chips (see commit
+		 * c96b9834032952492efbd2d1f5511fe225704918).
+		 */
+		bc->r6xx_nop_after_rel_dst = 1;
+	} else if (family == CHIP_RV770) {
+		bc->ar_handling = AR_HANDLE_NORMAL;
 		bc->r6xx_nop_after_rel_dst = 1;
 	} else {
 		bc->ar_handling = AR_HANDLE_NORMAL;