[llvm] [CodeGen] Use findPHICopyInsertPoint to put insert point (PR #155421)

[via llvm-commits]

https://github.com/AZero13 created https://github.com/llvm/llvm-project/pull/155421

None

>From 66b52755c863b30e334aec11b29e0745866b0fc6 Mon Sep 17 00:00:00 2001
From: AZero13 <gfunni234 at gmail.com>
Date: Tue, 26 Aug 2025 10:14:18 -0400
Subject: [PATCH] [CodeGen] Use findPHICopyInsertPoint to put insert point

---
 llvm/include/llvm/CodeGen/TailDuplicator.h |  7 +++--
 llvm/lib/CodeGen/TailDuplicator.cpp        | 33 +++++++++++-----------
 2 files changed, 20 insertions(+), 20 deletions(-)

diff --git a/llvm/include/llvm/CodeGen/TailDuplicator.h b/llvm/include/llvm/CodeGen/TailDuplicator.h
index 8b1f67c416c22..59bee594706ba 100644
--- a/llvm/include/llvm/CodeGen/TailDuplicator.h
+++ b/llvm/include/llvm/CodeGen/TailDuplicator.h
@@ -121,9 +121,10 @@ class TailDuplicator {
                      SmallVectorImpl<MachineBasicBlock *> &TDBBs,
                      SmallVectorImpl<MachineInstr *> &Copies,
                      SmallVectorImpl<MachineBasicBlock *> *CandidatePtr);
-  void appendCopies(MachineBasicBlock *MBB,
-                 SmallVectorImpl<std::pair<Register, RegSubRegPair>> &CopyInfos,
-                 SmallVectorImpl<MachineInstr *> &Copies);
+  void
+  appendCopies(MachineBasicBlock *MBB, MachineBasicBlock *IncomingBB,
+               SmallVectorImpl<std::pair<Register, RegSubRegPair>> &CopyInfos,
+               SmallVectorImpl<MachineInstr *> &Copies);
 
   void removeDeadBlock(
       MachineBasicBlock *MBB,
diff --git a/llvm/lib/CodeGen/TailDuplicator.cpp b/llvm/lib/CodeGen/TailDuplicator.cpp
index 5d720fbbf1c61..42bee02be2e00 100644
--- a/llvm/lib/CodeGen/TailDuplicator.cpp
+++ b/llvm/lib/CodeGen/TailDuplicator.cpp
@@ -12,6 +12,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/CodeGen/TailDuplicator.h"
+#include "PHIEliminationUtils.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/STLExtras.h"
@@ -651,14 +652,6 @@ bool TailDuplicator::shouldTailDuplicate(bool IsSimple,
     if (PreRegAlloc && MI.isCall())
       return false;
 
-    // TailDuplicator::appendCopies will erroneously place COPYs after
-    // INLINEASM_BR instructions after 4b0aa5724fea, which demonstrates the same
-    // bug that was fixed in f7a53d82c090.
-    // FIXME: Use findPHICopyInsertPoint() to find the correct insertion point
-    //        for the COPY when replacing PHIs.
-    if (MI.getOpcode() == TargetOpcode::INLINEASM_BR)
-      return false;
-
     if (MI.isBundle())
       InstrCount += MI.getBundleSize();
     else if (!MI.isPHI() && !MI.isMetaInstruction())
@@ -926,7 +919,7 @@ bool TailDuplicator::tailDuplicate(bool IsSimple, MachineBasicBlock *TailBB,
         duplicateInstruction(&MI, TailBB, PredBB, LocalVRMap, UsedByPhi);
       }
     }
-    appendCopies(PredBB, CopyInfos, Copies);
+    appendCopies(PredBB, TailBB, CopyInfos, Copies);
 
     NumTailDupAdded += TailBB->size() - 1; // subtract one for removed branch
 
@@ -994,7 +987,7 @@ bool TailDuplicator::tailDuplicate(bool IsSimple, MachineBasicBlock *TailBB,
           duplicateInstruction(MI, TailBB, PrevBB, LocalVRMap, UsedByPhi);
           MI->eraseFromParent();
         }
-        appendCopies(PrevBB, CopyInfos, Copies);
+        appendCopies(PrevBB, TailBB, CopyInfos, Copies);
       } else {
         TII->removeBranch(*PrevBB);
         // No PHIs to worry about, just splice the instructions over.
@@ -1058,7 +1051,7 @@ bool TailDuplicator::tailDuplicate(bool IsSimple, MachineBasicBlock *TailBB,
       // from PredBB.
       processPHI(&MI, TailBB, PredBB, LocalVRMap, CopyInfos, UsedByPhi, false);
     }
-    appendCopies(PredBB, CopyInfos, Copies);
+    appendCopies(PredBB, TailBB, CopyInfos, Copies);
   }
 
   return Changed;
@@ -1066,14 +1059,20 @@ bool TailDuplicator::tailDuplicate(bool IsSimple, MachineBasicBlock *TailBB,
 
 /// At the end of the block \p MBB generate COPY instructions between registers
 /// described by \p CopyInfos. Append resulting instructions to \p Copies.
-void TailDuplicator::appendCopies(MachineBasicBlock *MBB,
-      SmallVectorImpl<std::pair<Register, RegSubRegPair>> &CopyInfos,
-      SmallVectorImpl<MachineInstr*> &Copies) {
-  MachineBasicBlock::iterator Loc = MBB->getFirstTerminator();
+void TailDuplicator::appendCopies(
+    MachineBasicBlock *MBB, MachineBasicBlock *IncomingBB,
+    SmallVectorImpl<std::pair<Register, RegSubRegPair>> &CopyInfos,
+    SmallVectorImpl<MachineInstr *> &Copies) {
   const MCInstrDesc &CopyD = TII->get(TargetOpcode::COPY);
+
   for (auto &CI : CopyInfos) {
-    auto C = BuildMI(*MBB, Loc, DebugLoc(), CopyD, CI.first)
-                .addReg(CI.second.Reg, 0, CI.second.SubReg);
+    unsigned SrcReg = CI.second.Reg;
+    // Find a safe place to insert a copy for this particular source reg.
+    MachineBasicBlock::iterator Loc =
+        llvm::findPHICopyInsertPoint(MBB, IncomingBB, SrcReg);
+
+    MachineInstr *C = BuildMI(*MBB, Loc, DebugLoc(), CopyD, CI.first)
+                          .addReg(SrcReg, 0, CI.second.SubReg);
     Copies.push_back(C);
   }
 }