From 7d763c8b0ae6eee5f015fa82c744bff4c7ec8c8b Mon Sep 17 00:00:00 2001
From: Richard-Qin-X <richard.qin.001@gmail.com>
Date: Sat, 15 Aug 2026 03:11:22 +0800
Subject: [GlobalISel] Preserve worklists when moving CSE instructions

---
 backend/include/rcc/CodeGen/MachineBasicBlock.h  |  3 +++
 backend/lib/CodeGen/GlobalISel/CSEMIRBuilder.cpp |  8 +------
 backend/lib/CodeGen/MachineBasicBlock.cpp        | 28 ++++++++++++++++++++++++
 3 files changed, 32 insertions(+), 7 deletions(-)

(limited to 'backend')

diff --git a/backend/include/rcc/CodeGen/MachineBasicBlock.h b/backend/include/rcc/CodeGen/MachineBasicBlock.h
index da538db..10cc438 100644
--- a/backend/include/rcc/CodeGen/MachineBasicBlock.h
+++ b/backend/include/rcc/CodeGen/MachineBasicBlock.h
@@ -99,6 +99,9 @@ public:
                                                        MachineInstr &Instruction);
   [[nodiscard]] Expected<void> insertInstructionAfter(MachineInstr &Position,
                                                       MachineInstr &Instruction);
+  // Reorder linked instructions without reporting removal or insertion to the delegate.
+  [[nodiscard]] Expected<void> spliceInstructionBefore(MachineInstr &Position,
+                                                       MachineInstr &Instruction);
   [[nodiscard]] Expected<void> removeInstruction(MachineInstr &Instruction);
   void clearInstructions() noexcept;
 
diff --git a/backend/lib/CodeGen/GlobalISel/CSEMIRBuilder.cpp b/backend/lib/CodeGen/GlobalISel/CSEMIRBuilder.cpp
index e1fdaa6..caf9652 100644
--- a/backend/lib/CodeGen/GlobalISel/CSEMIRBuilder.cpp
+++ b/backend/lib/CodeGen/GlobalISel/CSEMIRBuilder.cpp
@@ -53,13 +53,7 @@ Expected<void> CSEMIRBuilder::makeInstructionDominate(MachineInstr &Instruction)
   }
   if (InsertBefore == nullptr || dominatesInsertionPoint(Instruction))
     return {};
-  auto Removed = Block->removeInstruction(Instruction);
-  if (!Removed)
-    return std::unexpected(Removed.error());
-  auto Inserted = Block->insertInstructionBefore(*InsertBefore, Instruction);
-  if (!Inserted)
-    return std::unexpected(Inserted.error());
-  return {};
+  return Block->spliceInstructionBefore(*InsertBefore, Instruction);
 }
 
 Expected<MachineInstr *>
diff --git a/backend/lib/CodeGen/MachineBasicBlock.cpp b/backend/lib/CodeGen/MachineBasicBlock.cpp
index 763a577..2de8f89 100644
--- a/backend/lib/CodeGen/MachineBasicBlock.cpp
+++ b/backend/lib/CodeGen/MachineBasicBlock.cpp
@@ -99,6 +99,34 @@ Expected<void> MachineBasicBlock::insertInstructionAfter(MachineInstr &Position,
   return {};
 }
 
+Expected<void> MachineBasicBlock::spliceInstructionBefore(MachineInstr &Position,
+                                                          MachineInstr &Instruction) {
+  if (Position.parent() != this || Instruction.parent() != this) {
+    return makeUnexpected(ErrorCode::InvalidArgument,
+                          "instruction splice requires two instructions in this block");
+  }
+  if (&Position == &Instruction || Instruction.NextInstruction == &Position)
+    return {};
+
+  if (Instruction.PreviousInstruction != nullptr)
+    Instruction.PreviousInstruction->NextInstruction = Instruction.NextInstruction;
+  else
+    FirstInstruction = Instruction.NextInstruction;
+  if (Instruction.NextInstruction != nullptr)
+    Instruction.NextInstruction->PreviousInstruction = Instruction.PreviousInstruction;
+  else
+    LastInstruction = Instruction.PreviousInstruction;
+
+  Instruction.PreviousInstruction = Position.PreviousInstruction;
+  Instruction.NextInstruction = &Position;
+  if (Position.PreviousInstruction != nullptr)
+    Position.PreviousInstruction->NextInstruction = &Instruction;
+  else
+    FirstInstruction = &Instruction;
+  Position.PreviousInstruction = &Instruction;
+  return {};
+}
+
 Expected<void> MachineBasicBlock::removeInstruction(MachineInstr &Instruction) {
   if (Instruction.parent() != this) {
     return makeUnexpected(ErrorCode::InvalidArgument, "instruction does not belong to this block");
-- 
cgit v1.2.3