From c58b94c376d4fbb257fef6fd62f4535f84de0c7d Mon Sep 17 00:00:00 2001
From: Jonathan G Rennison <j.g.rennison@gmail.com>
Date: Wed, 10 Aug 2022 19:39:12 +0100
Subject: [PATCH] VarAction2: DSE: Allow setting skip on zero flag on skippable
 procedures

---
 src/newgrf_optimiser.cpp | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/newgrf_optimiser.cpp b/src/newgrf_optimiser.cpp
index c3ff6eef1b..c82d928642 100644
--- a/src/newgrf_optimiser.cpp
+++ b/src/newgrf_optimiser.cpp
@@ -2593,6 +2593,11 @@ static std::bitset<256> HandleVarAction2DeadStoreElimination(DeterministicSprite
 					}
 					continue;
 				}
+				if (!anno->unskippable && anno->special_register_mask == 0 && IsEvalAdjustWithZeroLastValueAlwaysZero(adjust.operation)) {
+					/* No stores made in the procedure are required and there are no special stores or other features which make it unskippable.
+					 * Set DSGAF_SKIP_ON_ZERO if appropriate */
+					group->adjusts[i].adjust_flags |= DSGAF_SKIP_ON_ZERO;
+				}
 			}
 
 			need_var1C = false;