From e8ef184677f36cc729fc5893d7a8fa579923b21c Mon Sep 17 00:00:00 2001
From: Kenneth Graunke <kenneth@whitecape.org>
Date: Mon, 22 Jan 2024 02:06:02 -0800
Subject: [PATCH] intel/brw: Make register coalescing obey the g112-g127
 restriction

opt_register_coalesce can sometimes unpleasantly coalesce both
SENDS payload sources into the larger of the two registers.
This can break the assumption that the VGRFs for sources 2-3
must occupy no more than 16 registers, so they fit in g112-127.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27876>
---
 .../compiler/brw_fs_register_coalesce.cpp     | 39 ++++++++++++++++++-
 1 file changed, 38 insertions(+), 1 deletion(-)

diff --git a/src/intel/compiler/brw_fs_register_coalesce.cpp b/src/intel/compiler/brw_fs_register_coalesce.cpp
index 80ac7c2fd14..18b0d25d1ac 100644
--- a/src/intel/compiler/brw_fs_register_coalesce.cpp
+++ b/src/intel/compiler/brw_fs_register_coalesce.cpp
@@ -188,6 +188,42 @@ can_coalesce_vars(const fs_live_variables &live, const cfg_t *cfg,
    return true;
 }
 
+/**
+ * Check if coalescing this register would expand the size of the last
+ * SEND instruction's payload to more than would fit in g112-g127.
+ */
+static bool
+would_violate_eot_restriction(const brw::simple_allocator &alloc,
+                              const cfg_t *cfg,
+                              unsigned dst_reg, unsigned src_reg)
+{
+   if (alloc.sizes[dst_reg] > alloc.sizes[src_reg]) {
+      foreach_inst_in_block_reverse(fs_inst, send, cfg->last_block()) {
+         if (send->opcode != SHADER_OPCODE_SEND || !send->eot)
+            continue;
+
+         if ((send->src[2].file == VGRF && send->src[2].nr == src_reg) ||
+             (send->sources >= 4 &&
+              send->src[3].file == VGRF && send->src[3].nr == src_reg)) {
+            const unsigned s2 =
+               send->src[2].file == VGRF ? alloc.sizes[send->src[2].nr] : 0;
+            const unsigned s3 = send->sources >= 4 &&
+               send->src[3].file == VGRF ?
+               alloc.sizes[send->src[3].nr] : 0;
+
+            const unsigned increase =
+               alloc.sizes[dst_reg] - alloc.sizes[src_reg];
+
+            if (s2 + s3 + increase > 15)
+               return true;
+         }
+         break;
+      }
+   }
+
+   return false;
+}
+
 bool
 brw_fs_opt_register_coalesce(fs_visitor &s)
 {
@@ -267,7 +303,8 @@ brw_fs_opt_register_coalesce(fs_visitor &s)
          dst_var[i] = live.var_from_vgrf[dst_reg] + dst_reg_offset[i];
          src_var[i] = live.var_from_vgrf[src_reg] + i;
 
-         if (!can_coalesce_vars(live, s.cfg, block, inst, dst_var[i], src_var[i])) {
+         if (!can_coalesce_vars(live, s.cfg, block, inst, dst_var[i], src_var[i]) ||
+             would_violate_eot_restriction(s.alloc, s.cfg, dst_reg, src_reg)) {
             can_coalesce = false;
             src_reg = ~0u;
             break;