From 6e96c0df9702776a5ed8d43e852dcdd85ad47368 Mon Sep 17 00:00:00 2001
From: Connor Abbott <cwabbott0@gmail.com>
Date: Tue, 6 Feb 2024 14:14:04 -0500
Subject: [PATCH] ir3/ra: Fix bug with collect source handling

It can be the case that a collect and one of its sources are assigned
to non-overlapping parts of the same merge set, for example:

	ssa_1 = ...
	ssa_2 = ...
	ssa_3 = ...

	ssa_4 = collect ssa_1, ssa_2 (kill), ssa_3
	... = ssa_4 (kill)

	ssa_5 = collect ssa_1, ssa_3

	... = ssa_1 (kill)
	... = ssa_3 (kill)
	... = ssa_5 (kill)

If we merge the first collect first, we get a merge set:

	ssa_1 (offset 0)
	ssa_2 (offset 2)
	ssa_3 (offset 4)
	ssa_4 (offset 0)

Now, we decide to merge ssa_1 and ssa_5:

	ssa_1 (offset 0)
	ssa_2 (offset 2)
	ssa_3 (offset 4)
	ssa_4 (offset 0)
	ssa_5 (offset 0)

ssa_3 cannot become a child of ssa_5 in the interval tree, just like a
source not in the same merge set, so we should not remove it and then
reinsert it assuming that RA will make it a child of ssa_5.

This fixes an RA validation error in Farming Simulater.

Fixes: 0ffcb19 ("ir3: Rewrite register allocation")
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27497>
(cherry picked from commit aeed5fd98d47be122260bf0c232c2d8dfcd8d400)
---
 .pick_status.json          | 2 +-
 src/freedreno/ir3/ir3_ra.c | 8 +++++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/.pick_status.json b/.pick_status.json
index 9083c5150ee..4aff5a711c6 100644
--- a/.pick_status.json
+++ b/.pick_status.json
@@ -2894,7 +2894,7 @@
         "description": "ir3/ra: Fix bug with collect source handling",
         "nominated": true,
         "nomination_type": 1,
-        "resolution": 0,
+        "resolution": 1,
         "main_sha": null,
         "because_sha": "0ffcb19b9d9fbe902224542047c389a661fbf816",
         "notes": null
diff --git a/src/freedreno/ir3/ir3_ra.c b/src/freedreno/ir3/ir3_ra.c
index 070f67ba7ba..bcd8a527fd3 100644
--- a/src/freedreno/ir3/ir3_ra.c
+++ b/src/freedreno/ir3/ir3_ra.c
@@ -1715,8 +1715,14 @@ handle_collect(struct ra_ctx *ctx, struct ir3_instruction *instr)
 
       struct ra_interval *interval = &ctx->intervals[src->def->name];
 
-      if (src->def->merge_set != dst_set || interval->is_killed)
+      /* We only need special handling if the source's interval overlaps with
+       * the destination's interval.
+       */
+      if (src->def->interval_start >= instr->dsts[0]->interval_end ||
+          instr->dsts[0]->interval_start >= src->def->interval_end ||
+          interval->is_killed)
          continue;
+
       while (interval->interval.parent != NULL) {
          interval = ir3_reg_interval_to_ra_interval(interval->interval.parent);
       }