From 4648f967bdb769a954cdce0cf995a45d9aafdc55 Mon Sep 17 00:00:00 2001
From: "J. Gareth \"Curious Kit\" Moreton" <gareth@moreton-family.com>
Date: Mon, 24 Feb 2025 05:04:15 +0000
Subject: [PATCH]   * x86: Fixed bug in "MovMovMov2MovMovMov" optimisation
 where a register wasn't properly tracked

---
 compiler/x86/aoptx86.pas | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/compiler/x86/aoptx86.pas b/compiler/x86/aoptx86.pas
index b4fe4fef7e..375a60eafe 100644
--- a/compiler/x86/aoptx86.pas
+++ b/compiler/x86/aoptx86.pas
@@ -4369,6 +4369,13 @@ unit aoptx86;
                               begin
                                 taicpu(hp2).loadreg(0, p_SourceReg);
 
+                                TransferUsedRegs(TmpUsedRegs);
+                                UpdateUsedRegsBetween(TmpUsedRegs, tai(p.Next), hp1);
+                                { Make sure the register is allocated between these instructions
+                                  even though it doesn't change value, since it may cause
+                                  optimisations on a later pass to behave incorrectly. (Fixes #41155) }
+                                AllocRegBetween(p_SourceReg, hp1, hp2, TmpUsedRegs);
+
                                 DebugMsg(SPeepholeOptimization + 'Optimised register duplication and memory read (MovMovMov2MovMovMov)', p);
                                 Result := True;
                                 if taicpu(hp2).oper[1]^.reg = p_TargetReg then
@@ -4379,11 +4386,6 @@ unit aoptx86;
                                   end
                                 else
                                   begin
-                                    { Check to see if %reg2 is no longer in use }
-                                    TransferUsedRegs(TmpUsedRegs);
-                                    UpdateUsedRegsBetween(TmpUsedRegs, tai(p.Next), hp1);
-                                    UpdateUsedRegsBetween(TmpUsedRegs, tai(hp1.Next), hp2);
-
                                     if not RegUsedAfterInstruction(p_TargetReg, hp2, TmpUsedRegs) then
                                       begin
                                         DebugMsg(SPeepholeOptimization + 'Mov2Nop 5b done', p);