From 176b075129fbca397d5cbb4031310e4c5ae2d83f Mon Sep 17 00:00:00 2001
From: Rhys Perry <pendingchaos02@gmail.com>
Date: Thu, 15 Jan 2026 15:31:07 +0000
Subject: [PATCH] aco: prefer spilling smaller temporaries if it finishes
 spilling
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fossil-db stats seemed less positive when updating process_block() too.

fossil-db (navi31):
Totals from 41 (0.05% of 84369) affected shaders:
Instrs: 294758 -> 294694 (-0.02%); split: -0.11%, +0.09%
CodeSize: 1566136 -> 1564392 (-0.11%); split: -0.21%, +0.10%
SpillSGPRs: 2306 -> 2143 (-7.07%); split: -8.37%, +1.30%
Latency: 3877251 -> 3868194 (-0.23%); split: -0.29%, +0.05%
InvThroughput: 881747 -> 882352 (+0.07%); split: -0.01%, +0.08%
SClause: 6498 -> 6494 (-0.06%); split: -0.09%, +0.03%
Copies: 33582 -> 33900 (+0.95%); split: -0.23%, +1.18%
Branches: 6799 -> 6801 (+0.03%)
VALU: 192977 -> 192646 (-0.17%); split: -0.21%, +0.04%
SALU: 28082 -> 28395 (+1.11%); split: -0.27%, +1.39%
VOPD: 1939 -> 1959 (+1.03%); split: +1.19%, -0.15%

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/39690>
---
 src/amd/compiler/aco_spill.cpp | 29 +++++++++++++++++++----------
 1 file changed, 19 insertions(+), 10 deletions(-)

diff --git a/src/amd/compiler/aco_spill.cpp b/src/amd/compiler/aco_spill.cpp
index 6b57a47e235..c8b2467504d 100644
--- a/src/amd/compiler/aco_spill.cpp
+++ b/src/amd/compiler/aco_spill.cpp
@@ -169,6 +169,12 @@ struct spill_ctx {
       return next_spill_id++;
    }
 
+   std::pair<int, float> get_score(Temp var, RegisterDemand spills_needed)
+   {
+      int wasted = MAX2((int)var.size() - spills_needed[var.type()], 0);
+      return {-wasted, ssa_infos[var.id()].score()};
+   }
+
    uint32_t next_spill_id = 0;
 };
 
@@ -373,7 +379,7 @@ init_live_in_vars(spill_ctx& ctx, Block* block, unsigned block_idx)
       spills_needed.update(loop_call_spills);
       while (!spills_needed.empty()) {
          RegType type = get_spill_regtype(spills_needed);
-         float score = 0.0;
+         std::pair<int, float> score{INT_MIN, 0.0};
          unsigned remat = 0;
          Temp to_spill;
          for (unsigned t : live_in) {
@@ -383,14 +389,15 @@ init_live_in_vars(spill_ctx& ctx, Block* block, unsigned block_idx)
                continue;
 
             unsigned can_remat = ctx.remat.count(var);
-            if (can_remat > remat || (can_remat == remat && ctx.ssa_infos[t].score() > score)) {
+            std::pair<int, float> var_score = ctx.get_score(var, spills_needed);
+            if (can_remat > remat || (can_remat == remat && var_score > score)) {
                to_spill = var;
-               score = ctx.ssa_infos[t].score();
+               score = var_score;
                remat = can_remat;
             }
          }
 
-         if (score == 0.0) {
+         if (score.second == 0.0) {
             spills_needed[type] = 0;
             continue;
          }
@@ -414,7 +421,7 @@ init_live_in_vars(spill_ctx& ctx, Block* block, unsigned block_idx)
 
       spills_needed = reg_pressure - ctx.target_pressure;
       while (!spills_needed.empty()) {
-         float score = 0;
+         std::pair<int, float> score{INT_MIN, 0.0};
          Temp to_spill = Temp();
          RegType type = get_spill_regtype(spills_needed);
          for (aco_ptr<Instruction>& phi : block->instructions) {
@@ -423,10 +430,11 @@ init_live_in_vars(spill_ctx& ctx, Block* block, unsigned block_idx)
             if (!phi->definitions[0].isTemp() || phi->definitions[0].isKill())
                continue;
             Temp var = phi->definitions[0].getTemp();
+            std::pair<int, float> var_score = ctx.get_score(var, spills_needed);
             if (var.type() == type && !ctx.spills_entry[block_idx].count(var) &&
-                ctx.ssa_infos[var.id()].score() > score && is_spillable(ctx, var)) {
+                var_score > score && is_spillable(ctx, var)) {
                to_spill = var;
-               score = ctx.ssa_infos[var.id()].score();
+               score = var_score;
             }
          }
          assert(to_spill != Temp());
@@ -554,16 +562,17 @@ init_live_in_vars(spill_ctx& ctx, Block* block, unsigned block_idx)
       std::map<Temp, bool>::iterator it = partial_spills.begin();
       Temp to_spill = Temp();
       bool is_partial_spill = false;
-      float score = 0.0;
+      std::pair<int, float> score{INT_MIN, 0.0};
       RegType type = get_spill_regtype(spills_needed);
 
       while (it != partial_spills.end()) {
          assert(!ctx.spills_entry[block_idx].count(it->first));
 
+         std::pair<int, float> var_score = ctx.get_score(it->first, spills_needed);
          if (it->first.type() == type && is_spillable(ctx, it->first) &&
              ((it->second && !is_partial_spill) ||
-              (it->second == is_partial_spill && ctx.ssa_infos[it->first.id()].score() > score))) {
-            score = ctx.ssa_infos[it->first.id()].score();
+              (it->second == is_partial_spill && var_score > score))) {
+            score = var_score;
             to_spill = it->first;
             is_partial_spill = it->second;
          }