From e68bd742451aae5fcdf280e823d2829e11d184da Mon Sep 17 00:00:00 2001
From: Jim Grosbach <grosbach@apple.com>
Date: Sat, 6 Mar 2010 03:28:39 +0000
Subject: [PATCH] Thumb1 epilogue code generation needs to take into account
 that callee-saved registers may be restored via a pop instruction, not just a
 tRestore. This fixes nightly test 471.omnetep for Thumb1.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@97867 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Target/ARM/Thumb1RegisterInfo.cpp | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/lib/Target/ARM/Thumb1RegisterInfo.cpp b/lib/Target/ARM/Thumb1RegisterInfo.cpp
index b61ce29aab8..163d1e9a0dd 100644
--- a/lib/Target/ARM/Thumb1RegisterInfo.cpp
+++ b/lib/Target/ARM/Thumb1RegisterInfo.cpp
@@ -778,9 +778,19 @@ static bool isCalleeSavedRegister(unsigned Reg, const unsigned *CSRegs) {
 }
 
 static bool isCSRestore(MachineInstr *MI, const unsigned *CSRegs) {
-  return (MI->getOpcode() == ARM::tRestore &&
-          MI->getOperand(1).isFI() &&
-          isCalleeSavedRegister(MI->getOperand(0).getReg(), CSRegs));
+  if (MI->getOpcode() == ARM::tRestore &&
+      MI->getOperand(1).isFI() &&
+      isCalleeSavedRegister(MI->getOperand(0).getReg(), CSRegs))
+    return true;
+  else if (MI->getOpcode() == ARM::tPOP) {
+    // The first three operands are predicates and such. The last two are
+    // imp-def and imp-use of SP. Check everything in between.
+    for (int i = 3, e = MI->getNumOperands() - 2; i != e; ++i)
+      if (!isCalleeSavedRegister(MI->getOperand(i).getReg(), CSRegs))
+        return false;
+    return true;
+  }
+  return false;
 }
 
 void Thumb1RegisterInfo::emitEpilogue(MachineFunction &MF,
@@ -794,13 +804,13 @@ void Thumb1RegisterInfo::emitEpilogue(MachineFunction &MF,
   ARMFunctionInfo *AFI = MF.getInfo<ARMFunctionInfo>();
   unsigned VARegSaveSize = AFI->getVarArgsRegSaveSize();
   int NumBytes = (int)MFI->getStackSize();
+  const unsigned *CSRegs = getCalleeSavedRegs();
 
   if (!AFI->hasStackFrame()) {
     if (NumBytes != 0)
       emitSPUpdate(MBB, MBBI, TII, dl, *this, NumBytes);
   } else {
     // Unwind MBBI to point to first LDR / VLDRD.
-    const unsigned *CSRegs = getCalleeSavedRegs();
     if (MBBI != MBB.begin()) {
       do
         --MBBI;
@@ -836,6 +846,9 @@ void Thumb1RegisterInfo::emitEpilogue(MachineFunction &MF,
   }
 
   if (VARegSaveSize) {
+    // Move back past the callee-saved register restoration
+    while (MBBI != MBB.end() && isCSRestore(MBBI, CSRegs))
+      ++MBBI;
     // Epilogue for vararg functions: pop LR to R3 and branch off it.
     AddDefaultPred(BuildMI(MBB, MBBI, dl, TII.get(ARM::tPOP)))
       .addReg(0) // No write back.
@@ -845,6 +858,7 @@ void Thumb1RegisterInfo::emitEpilogue(MachineFunction &MF,
 
     BuildMI(MBB, MBBI, dl, TII.get(ARM::tBX_RET_vararg))
       .addReg(ARM::R3, RegState::Kill);
+    // erase the old tBX_RET instruction
     MBB.erase(MBBI);
   }
 }