0063-Xtensa-Remove-unnecessary-MOVSP-in-epilogue.patch

From b06bee17f359950d3d7de15ac1c9fcb08f8075d2 Mon Sep 17 00:00:00 2001
From: Andrei Safronov <safronov@espressif.com>
Date: Wed, 5 Apr 2023 00:59:10 +0300
Subject: [PATCH 063/158] [Xtensa] Remove unnecessary MOVSP in epilogue.

---
 llvm/lib/Target/Xtensa/XtensaFrameLowering.cpp | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/Target/Xtensa/XtensaFrameLowering.cpp b/llvm/lib/Target/Xtensa/XtensaFrameLowering.cpp
index 31ae43565974..aabdc73b2f6e 100644
--- a/llvm/lib/Target/Xtensa/XtensaFrameLowering.cpp
+++ b/llvm/lib/Target/Xtensa/XtensaFrameLowering.cpp
@@ -247,8 +247,13 @@ void XtensaFrameLowering::emitEpilogue(MachineFunction &MF,
     for (unsigned i = 0; i < MFI.getCalleeSavedInfo().size(); ++i)
       --I;
     if (STI.isWinABI()) {
-      // Insert instruction "movsp $sp, $fp" at this location.
-      BuildMI(MBB, I, dl, TII.get(Xtensa::MOVSP), SP).addReg(FP);
+      // In most architectures, we need to explicitly restore the stack pointer
+      // before returning.
+      //
+      // For Xtensa Windowed Register option, it is not needed to explicitly
+      // restore the stack pointer. Reason being is that on function return,
+      // the window of the caller (including the old stack pointer) gets
+      // restored anyways.
     } else {
       BuildMI(MBB, I, dl, TII.get(Xtensa::OR), SP).addReg(FP).addReg(FP);
     }
-- 
2.40.1