From 022705b03acb1c0837117fdfd2446b4c445734ab Mon Sep 17 00:00:00 2001
From: Rhys Perry <pendingchaos02@gmail.com>
Date: Wed, 29 Oct 2025 12:56:51 +0000
Subject: [PATCH] aco/ra: create vectors for affinities of split definitions

For example:
a = ...
b = ...
if {
   c, d = split
}
phi(a, c)
phi(b, d)

This patch will allocate 'a' and 'b' as a vector.

fossil-db (navi31):
Totals from 2566 (3.21% of 79825) affected shaders:
MaxWaves: 59941 -> 59939 (-0.00%)
Instrs: 9160792 -> 9146435 (-0.16%); split: -0.18%, +0.02%
CodeSize: 48178860 -> 48122308 (-0.12%); split: -0.14%, +0.02%
VGPRs: 189756 -> 190320 (+0.30%); split: -0.04%, +0.34%
Latency: 85163405 -> 84972598 (-0.22%); split: -0.29%, +0.07%
InvThroughput: 14490059 -> 14464958 (-0.17%); split: -0.23%, +0.06%
VClause: 197594 -> 197639 (+0.02%); split: -0.01%, +0.03%
Copies: 794103 -> 781555 (-1.58%); split: -1.81%, +0.23%
Branches: 271605 -> 271592 (-0.00%); split: -0.02%, +0.01%
VALU: 5330323 -> 5318069 (-0.23%); split: -0.26%, +0.03%
SALU: 1130031 -> 1129658 (-0.03%); split: -0.05%, +0.01%
VOPD: 2511 -> 2503 (-0.32%); split: +0.48%, -0.80%

fossil-db (navi21):
Totals from 37512 (46.99% of 79825) affected shaders:
Instrs: 26725535 -> 26672372 (-0.20%); split: -0.22%, +0.03%
CodeSize: 141296848 -> 141075516 (-0.16%); split: -0.18%, +0.02%
VGPRs: 1556584 -> 1556216 (-0.02%); split: -0.21%, +0.19%
Latency: 146266991 -> 146202343 (-0.04%); split: -0.20%, +0.16%
InvThroughput: 33932575 -> 33872374 (-0.18%); split: -0.23%, +0.06%
VClause: 501929 -> 501949 (+0.00%); split: -0.27%, +0.27%
SClause: 592642 -> 592655 (+0.00%); split: -0.00%, +0.00%
Copies: 2600040 -> 2550475 (-1.91%); split: -2.16%, +0.25%
Branches: 857553 -> 857465 (-0.01%); split: -0.03%, +0.02%
VALU: 15668495 -> 15619140 (-0.31%); split: -0.35%, +0.04%
SALU: 4634670 -> 4633930 (-0.02%); split: -0.03%, +0.02%

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
---
 src/amd/compiler/aco_register_allocation.cpp | 45 ++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/src/amd/compiler/aco_register_allocation.cpp b/src/amd/compiler/aco_register_allocation.cpp
index 3c4b029c058..c4b1e5515e3 100644
--- a/src/amd/compiler/aco_register_allocation.cpp
+++ b/src/amd/compiler/aco_register_allocation.cpp
@@ -3347,6 +3347,51 @@ get_affinities(ra_ctx& ctx)
             ctx.vectors[vec[0].id()] = it->second;
       }
    }
+
+   /* If split definitions have affinities with other temporaries, try to allocate those temporaries
+    * as a vector. */
+   for (std::pair<uint32_t, Instruction *> pair : ctx.split_vectors) {
+      Instruction *split = pair.second;
+
+      vector_info info;
+      info.num_parts = split->definitions.size();
+
+      unsigned num_temps = 0;
+      for (unsigned i = 0; i < split->definitions.size(); i++) {
+         Definition def = split->definitions[i];
+         uint32_t id = ctx.assignments[def.tempId()].affinity;
+         if (!id || def.regClass().type() != split->operands[0].regClass().type())
+            continue;
+
+         if (!info.parts) {
+            info.parts =
+               (Operand*)ctx.memory.allocate(sizeof(Operand) * info.num_parts, alignof(Operand));
+            for (unsigned j = 0; j < split->definitions.size(); j++)
+               info.parts[j] = Operand(split->definitions[j].regClass());
+         }
+
+         info.parts[i] = Operand(Temp(id, ctx.program->temp_rc[id]));
+         num_temps++;
+      }
+      if (!num_temps)
+         continue;
+
+      for (unsigned i = 0; i < split->definitions.size(); i++) {
+         uint32_t id = info.parts[i].tempId();
+         if (!id)
+            continue;
+
+         /* If the new vector affinities only includes one temporary, only overwrite the old one if
+          * the new one is stronger. */
+         auto vec_it = ctx.vectors.find(id);
+         if (num_temps == 1 && vec_it != ctx.vectors.end() &&
+             (!vec_it->second.is_weak || info.is_weak))
+            continue;
+
+         info.index = i;
+         ctx.vectors[id] = info;
+      }
+   }
 }
 
 void