From bbde6be841b22667179c6e75682c40e1484a4bf2 Mon Sep 17 00:00:00 2001
From: Elizaveta Noskova <159026035+enoskova-sc@users.noreply.github.com>
Date: Tue, 12 Aug 2025 16:34:29 +0300
Subject: [llvm] Support multiple save/restore points in mir (#119357)

Currently mir supports only one save and one restore point
specification:

```
  savePoint:       '%bb.1'
  restorePoint:    '%bb.2'
```

This patch provide possibility to have multiple save and multiple
restore points in mir:

```
  savePoints:
    - point:           '%bb.1'
  restorePoints:
    - point:           '%bb.2'
```

Shrink-Wrap points split Part 3.
RFC:
https://discourse.llvm.org/t/shrink-wrap-save-restore-points-splitting/83581

Part 1: https://github.com/llvm/llvm-project/pull/117862
Part 2: https://github.com/llvm/llvm-project/pull/119355
Part 4: https://github.com/llvm/llvm-project/pull/119358
Part 5: https://github.com/llvm/llvm-project/pull/119359
---
 llvm/lib/CodeGen/PrologEpilogInserter.cpp | 27 ++++++++++++++++++---------
 1 file changed, 18 insertions(+), 9 deletions(-)

(limited to 'llvm/lib/CodeGen/PrologEpilogInserter.cpp')

diff --git a/llvm/lib/CodeGen/PrologEpilogInserter.cpp b/llvm/lib/CodeGen/PrologEpilogInserter.cpp
index 7b751ba..8fc0748 100644
--- a/llvm/lib/CodeGen/PrologEpilogInserter.cpp
+++ b/llvm/lib/CodeGen/PrologEpilogInserter.cpp
@@ -351,8 +351,8 @@ bool PEIImpl::run(MachineFunction &MF) {
   delete RS;
   SaveBlocks.clear();
   RestoreBlocks.clear();
-  MFI.setSavePoint(nullptr);
-  MFI.setRestorePoint(nullptr);
+  MFI.setSavePoints({});
+  MFI.setRestorePoints({});
   return true;
 }
 
@@ -423,16 +423,18 @@ void PEIImpl::calculateCallFrameInfo(MachineFunction &MF) {
 /// callee-saved registers, and placing prolog and epilog code.
 void PEIImpl::calculateSaveRestoreBlocks(MachineFunction &MF) {
   const MachineFrameInfo &MFI = MF.getFrameInfo();
-
   // Even when we do not change any CSR, we still want to insert the
   // prologue and epilogue of the function.
   // So set the save points for those.
 
   // Use the points found by shrink-wrapping, if any.
-  if (MFI.getSavePoint()) {
-    SaveBlocks.push_back(MFI.getSavePoint());
-    assert(MFI.getRestorePoint() && "Both restore and save must be set");
-    MachineBasicBlock *RestoreBlock = MFI.getRestorePoint();
+  if (!MFI.getSavePoints().empty()) {
+    assert(MFI.getSavePoints().size() == 1 &&
+           "Multiple save points are not yet supported!");
+    SaveBlocks.push_back(MFI.getSavePoints().front());
+    assert(MFI.getRestorePoints().size() == 1 &&
+           "Multiple restore points are not yet supported!");
+    MachineBasicBlock *RestoreBlock = MFI.getRestorePoints().front();
     // If RestoreBlock does not have any successor and is not a return block
     // then the end point is unreachable and we do not need to insert any
     // epilogue.
@@ -558,7 +560,11 @@ static void updateLiveness(MachineFunction &MF) {
   SmallPtrSet<MachineBasicBlock *, 8> Visited;
   SmallVector<MachineBasicBlock *, 8> WorkList;
   MachineBasicBlock *Entry = &MF.front();
-  MachineBasicBlock *Save = MFI.getSavePoint();
+
+  assert(MFI.getSavePoints().size() < 2 &&
+         "Multiple save points not yet supported!");
+  MachineBasicBlock *Save =
+      MFI.getSavePoints().empty() ? nullptr : MFI.getSavePoints().front();
 
   if (!Save)
     Save = Entry;
@@ -569,7 +575,10 @@ static void updateLiveness(MachineFunction &MF) {
   }
   Visited.insert(Save);
 
-  MachineBasicBlock *Restore = MFI.getRestorePoint();
+  assert(MFI.getRestorePoints().size() < 2 &&
+         "Multiple restore points not yet supported!");
+  MachineBasicBlock *Restore =
+      MFI.getRestorePoints().empty() ? nullptr : MFI.getRestorePoints().front();
   if (Restore)
     // By construction Restore cannot be visited, otherwise it
     // means there exists a path to Restore that does not go
-- 
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