4 files changed, 21 insertions, 0 deletions
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 72c76878f2c..bf07b600004 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -9615,6 +9615,8 @@ void SelectionDAGISel::LowerArguments(const Function &F) {
       Flags.setOrigAlign(OriginalAlignment);
       if (ArgCopyElisionCandidates.count(&Arg))
         Flags.setCopyElisionCandidate();
+      if (Arg.hasAttribute(Attribute::Returned))
+        Flags.setReturned();
 
       MVT RegisterVT = TLI->getRegisterTypeForCallingConv(
           *CurDAG->getContext(), F.getCallingConv(), VT);
diff --git a/llvm/lib/Target/ARM/ARMFrameLowering.cpp b/llvm/lib/Target/ARM/ARMFrameLowering.cpp
index bedb779bcba..7ae0c6ab3cf 100644
--- a/llvm/lib/Target/ARM/ARMFrameLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMFrameLowering.cpp
@@ -2097,6 +2097,12 @@ void ARMFrameLowering::determineCalleeSaves(MachineFunction &MF,
     AFI->setLRIsSpilledForFarJump(true);
   }
   AFI->setLRIsSpilled(SavedRegs.test(ARM::LR));
+
+  // If we have the "returned" parameter attribute which guarantees that we
+  // return the value which was passed in r0 unmodified (e.g. C++ 'structors),
+  // record that fact for IPRA.
+  if (AFI->getPreservesR0())
+    SavedRegs.set(ARM::R0);
 }
 
 MachineBasicBlock::iterator ARMFrameLowering::eliminateCallFramePseudoInstr(
diff --git a/llvm/lib/Target/ARM/ARMISelLowering.cpp b/llvm/lib/Target/ARM/ARMISelLowering.cpp
index 18bb9bf3ecc..ee619353897 100644
--- a/llvm/lib/Target/ARM/ARMISelLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMISelLowering.cpp
@@ -3898,6 +3898,12 @@ SDValue ARMTargetLowering::LowerFormalArguments(
         // Transform the arguments in physical registers into virtual ones.
         unsigned Reg = MF.addLiveIn(VA.getLocReg(), RC);
         ArgValue = DAG.getCopyFromReg(Chain, dl, Reg, RegVT);
+
+        // If this value is passed in r0 and has the returned attribute (e.g.
+        // C++ 'structors), record this fact for later use.
+        if (VA.getLocReg() == ARM::R0 && Ins[VA.getValNo()].Flags.isReturned()) {
+          AFI->setPreservesR0();
+        }
       }
 
       // If this is an 8 or 16-bit value, it is really passed promoted
diff --git a/llvm/lib/Target/ARM/ARMMachineFunctionInfo.h b/llvm/lib/Target/ARM/ARMMachineFunctionInfo.h
index 90d794cd27b..e80c2c64123 100644
--- a/llvm/lib/Target/ARM/ARMMachineFunctionInfo.h
+++ b/llvm/lib/Target/ARM/ARMMachineFunctionInfo.h
@@ -130,6 +130,10 @@ class ARMFunctionInfo : public MachineFunctionInfo {
   /// The amount the literal pool has been increasedby due to promoted globals.
   int PromotedGlobalsIncrease = 0;
 
+  /// True if r0 will be preserved by a call to this function (e.g. C++
+  /// con/destructors).
+  bool PreservesR0 = false;
+
 public:
   ARMFunctionInfo() = default;
 
@@ -247,6 +251,9 @@ public:
   }
 
   DenseMap<unsigned, unsigned> EHPrologueRemappedRegs;
+
+  void setPreservesR0() { PreservesR0 = true; }
+  bool getPreservesR0() const { return PreservesR0; }
 };
 
 } // end namespace llvm