Add "Restored" flag to CalleeSavedInfo

The liveness-tracking code assumes that the registers that were saved
in the function's prolog are live outside of the function. Specifically,
that registers that were saved are also live-on-exit from the function.
This isn't always the case as illustrated by the LR register on ARM.

Differential Revision: https://reviews.llvm.org/D36160


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@310619 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/MachineFrameInfo.h

@@ -31,15 +31,30 @@ class AllocaInst;
 class CalleeSavedInfo {
   unsigned Reg;
   int FrameIdx;
+  /// Flag indicating whether the register is actually restored in the epilog.
+  /// In most cases, if a register is saved, it is also restored. There are
+  /// some situations, though, when this is not the case. For example, the
+  /// LR register on ARM is usually saved, but on exit from the function its
+  /// saved value may be loaded directly into PC. Since liveness tracking of
+  /// physical registers treats callee-saved registers are live outside of
+  /// the function, LR would be treated as live-on-exit, even though in these
+  /// scenarios it is not. This flag is added to indicate that the saved
+  /// register described by this object is not restored in the epilog.
+  /// The long-term solution is to model the liveness of callee-saved registers
+  /// by implicit uses on the return instructions, however, the required
+  /// changes in the ARM backend would be quite extensive.
+  bool Restored;
 
 public:
   explicit CalleeSavedInfo(unsigned R, int FI = 0)
-  : Reg(R), FrameIdx(FI) {}
+  : Reg(R), FrameIdx(FI), Restored(true) {}
 
   // Accessors.
   unsigned getReg()                        const { return Reg; }
   int getFrameIdx()                        const { return FrameIdx; }
   void setFrameIdx(int FI)                       { FrameIdx = FI; }
+  bool isRestored()                        const { return Restored; }
+  void setRestored(bool R)                       { Restored = R; }
 };
 
 /// The MachineFrameInfo class represents an abstract stack frame until
@@ -667,6 +682,8 @@ public:
   const std::vector<CalleeSavedInfo> &getCalleeSavedInfo() const {
     return CSInfo;
   }
+  /// \copydoc getCalleeSavedInfo()
+  std::vector<CalleeSavedInfo> &getCalleeSavedInfo() { return CSInfo; }
 
   /// Used by prolog/epilog inserter to set the function's callee saved
   /// information.

include/llvm/Target/TargetFrameLowering.h

@@ -193,10 +193,12 @@ public:
   /// restoreCalleeSavedRegisters - Issues instruction(s) to restore all callee
   /// saved registers and returns true if it isn't possible / profitable to do
   /// so by issuing a series of load instructions via loadRegToStackSlot().
+  /// If it returns true, and any of the registers in CSI is not restored,
+  /// it sets the corresponding Restored flag in CSI to false.
   /// Returns false otherwise.
   virtual bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
                                            MachineBasicBlock::iterator MI,
-                                        const std::vector<CalleeSavedInfo> &CSI,
+                                           std::vector<CalleeSavedInfo> &CSI,
                                         const TargetRegisterInfo *TRI) const {
     return false;
   }

lib/CodeGen/LivePhysRegs.cpp

@@ -192,7 +192,8 @@ void LivePhysRegs::addLiveOutsNoPristines(const MachineBasicBlock &MBB) {
     const MachineFrameInfo &MFI = MF.getFrameInfo();
     if (MFI.isCalleeSavedInfoValid()) {
       for (const CalleeSavedInfo &Info : MFI.getCalleeSavedInfo())
-        addReg(Info.getReg());
+        if (Info.isRestored())
+          addReg(Info.getReg());
     }
   }
 }

lib/CodeGen/PrologEpilogInserter.cpp

@@ -489,7 +489,7 @@ static void insertCSRSaves(MachineBasicBlock &SaveBlock,
 
 /// Insert restore code for the callee-saved registers used in the function.
 static void insertCSRRestores(MachineBasicBlock &RestoreBlock,
-                              ArrayRef<CalleeSavedInfo> CSI) {
+                              std::vector<CalleeSavedInfo> &CSI) {
   MachineFunction &Fn = *RestoreBlock.getParent();
   const TargetInstrInfo &TII = *Fn.getSubtarget().getInstrInfo();
   const TargetFrameLowering *TFI = Fn.getSubtarget().getFrameLowering();
@@ -534,7 +534,7 @@ static void doSpillCalleeSavedRegs(MachineFunction &Fn, RegScavenger *RS,
   if (!F->hasFnAttribute(Attribute::Naked)) {
     MFI.setCalleeSavedInfoValid(true);
 
-    ArrayRef<CalleeSavedInfo> CSI = MFI.getCalleeSavedInfo();
+    std::vector<CalleeSavedInfo> &CSI = MFI.getCalleeSavedInfo();
     if (!CSI.empty()) {
       for (MachineBasicBlock *SaveBlock : SaveBlocks) {
         insertCSRSaves(*SaveBlock, CSI);

lib/Target/AArch64/AArch64FrameLowering.cpp

@@ -1092,7 +1092,7 @@ bool AArch64FrameLowering::spillCalleeSavedRegisters(
 
 bool AArch64FrameLowering::restoreCalleeSavedRegisters(
     MachineBasicBlock &MBB, MachineBasicBlock::iterator MI,
-    const std::vector<CalleeSavedInfo> &CSI,
+    std::vector<CalleeSavedInfo> &CSI,
     const TargetRegisterInfo *TRI) const {
   MachineFunction &MF = *MBB.getParent();
   const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();

lib/Target/AArch64/AArch64FrameLowering.h

@@ -50,7 +50,7 @@ public:
 
   bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
                                   MachineBasicBlock::iterator MI,
-                                  const std::vector<CalleeSavedInfo> &CSI,
+                                  std::vector<CalleeSavedInfo> &CSI,
                                   const TargetRegisterInfo *TRI) const override;
 
   /// \brief Can this function use the red zone for local allocations.

lib/Target/ARM/ARMFrameLowering.cpp

@@ -1019,7 +1019,7 @@ void ARMFrameLowering::emitPushInst(MachineBasicBlock &MBB,
 
 void ARMFrameLowering::emitPopInst(MachineBasicBlock &MBB,
                                    MachineBasicBlock::iterator MI,
-                                   const std::vector<CalleeSavedInfo> &CSI,
+                                   std::vector<CalleeSavedInfo> &CSI,
                                    unsigned LdmOpc, unsigned LdrOpc,
                                    bool isVarArg, bool NoGap,
                                    bool(*Func)(unsigned, bool),
@@ -1090,9 +1090,18 @@ void ARMFrameLowering::emitPopInst(MachineBasicBlock &MBB,
                                     .add(predOps(ARMCC::AL));
       for (unsigned i = 0, e = Regs.size(); i < e; ++i)
         MIB.addReg(Regs[i], getDefRegState(true));
-      if (DeleteRet && MI != MBB.end()) {
-        MIB.copyImplicitOps(*MI);
-        MI->eraseFromParent();
+      if (DeleteRet) {
+        if (MI != MBB.end()) {
+          MIB.copyImplicitOps(*MI);
+          MI->eraseFromParent();
+        }
+        // If LR is not restored, mark it in CSI.
+        for (CalleeSavedInfo &I : CSI) {
+          if (I.getReg() != ARM::LR)
+            continue;
+          I.setRestored(false);
+          break;
+        }
       }
       MI = MIB;
     } else if (Regs.size() == 1) {
@@ -1421,7 +1430,7 @@ bool ARMFrameLowering::spillCalleeSavedRegisters(MachineBasicBlock &MBB,
 
 bool ARMFrameLowering::restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
                                         MachineBasicBlock::iterator MI,
-                                        const std::vector<CalleeSavedInfo> &CSI,
+                                        std::vector<CalleeSavedInfo> &CSI,
                                         const TargetRegisterInfo *TRI) const {
   if (CSI.empty())
     return false;

lib/Target/ARM/ARMFrameLowering.h

@@ -38,7 +38,7 @@ public:
 
   bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
                                   MachineBasicBlock::iterator MI,
-                                  const std::vector<CalleeSavedInfo> &CSI,
+                                  std::vector<CalleeSavedInfo> &CSI,
                                   const TargetRegisterInfo *TRI) const override;
 
   bool noFramePointerElim(const MachineFunction &MF) const override;
@@ -69,7 +69,7 @@ public:
                     bool(*Func)(unsigned, bool), unsigned NumAlignedDPRCS2Regs,
                     unsigned MIFlags = 0) const;
   void emitPopInst(MachineBasicBlock &MBB, MachineBasicBlock::iterator MI,
-                   const std::vector<CalleeSavedInfo> &CSI, unsigned LdmOpc,
+                   std::vector<CalleeSavedInfo> &CSI, unsigned LdmOpc,
                    unsigned LdrOpc, bool isVarArg, bool NoGap,
                    bool(*Func)(unsigned, bool),
                    unsigned NumAlignedDPRCS2Regs) const;

lib/Target/ARM/Thumb1FrameLowering.cpp

@@ -780,7 +780,7 @@ spillCalleeSavedRegisters(MachineBasicBlock &MBB,
 bool Thumb1FrameLowering::
 restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
                             MachineBasicBlock::iterator MI,
-                            const std::vector<CalleeSavedInfo> &CSI,
+                            std::vector<CalleeSavedInfo> &CSI,
                             const TargetRegisterInfo *TRI) const {
   if (CSI.empty())
     return false;

lib/Target/ARM/Thumb1FrameLowering.h

@@ -36,7 +36,7 @@ public:
                                  const TargetRegisterInfo *TRI) const override;
   bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
                                   MachineBasicBlock::iterator MI,
-                                  const std::vector<CalleeSavedInfo> &CSI,
+                                  std::vector<CalleeSavedInfo> &CSI,
                                   const TargetRegisterInfo *TRI) const override;
 
   bool hasReservedCallFrame(const MachineFunction &MF) const override;

lib/Target/AVR/AVRFrameLowering.cpp

@@ -275,7 +275,7 @@ bool AVRFrameLowering::spillCalleeSavedRegisters(
 
 bool AVRFrameLowering::restoreCalleeSavedRegisters(
     MachineBasicBlock &MBB, MachineBasicBlock::iterator MI,
-    const std::vector<CalleeSavedInfo> &CSI,
+    std::vector<CalleeSavedInfo> &CSI,
     const TargetRegisterInfo *TRI) const {
   if (CSI.empty()) {
     return false;

lib/Target/AVR/AVRFrameLowering.h

@@ -30,7 +30,7 @@ public:
   bool
   restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
                               MachineBasicBlock::iterator MI,
-                              const std::vector<CalleeSavedInfo> &CSI,
+                              std::vector<CalleeSavedInfo> &CSI,
                               const TargetRegisterInfo *TRI) const override;
   bool hasReservedCallFrame(const MachineFunction &MF) const override;
   bool canSimplifyCallFramePseudos(const MachineFunction &MF) const override;

lib/Target/Hexagon/HexagonFrameLowering.h

@@ -48,7 +48,7 @@ public:
   }
 
   bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
-      MachineBasicBlock::iterator MI, const std::vector<CalleeSavedInfo> &CSI,
+      MachineBasicBlock::iterator MI, std::vector<CalleeSavedInfo> &CSI,
       const TargetRegisterInfo *TRI) const override {
     return true;
   }

lib/Target/MSP430/MSP430FrameLowering.cpp

@@ -206,7 +206,7 @@ MSP430FrameLowering::spillCalleeSavedRegisters(MachineBasicBlock &MBB,
 bool
 MSP430FrameLowering::restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
                                                  MachineBasicBlock::iterator MI,
-                                        const std::vector<CalleeSavedInfo> &CSI,
+                                        std::vector<CalleeSavedInfo> &CSI,
                                         const TargetRegisterInfo *TRI) const {
   if (CSI.empty())
     return false;

lib/Target/MSP430/MSP430FrameLowering.h

@@ -40,7 +40,7 @@ public:
                                  const TargetRegisterInfo *TRI) const override;
   bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
                                   MachineBasicBlock::iterator MI,
-                                  const std::vector<CalleeSavedInfo> &CSI,
+                                  std::vector<CalleeSavedInfo> &CSI,
                                   const TargetRegisterInfo *TRI) const override;
 
   bool hasFP(const MachineFunction &MF) const override;

lib/Target/Mips/Mips16FrameLowering.cpp

@@ -143,7 +143,7 @@ spillCalleeSavedRegisters(MachineBasicBlock &MBB,
 
 bool Mips16FrameLowering::restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
                                           MachineBasicBlock::iterator MI,
-                                       const std::vector<CalleeSavedInfo> &CSI,
+                                       std::vector<CalleeSavedInfo> &CSI,
                                        const TargetRegisterInfo *TRI) const {
   //
   // Registers RA,S0,S1 are the callee saved registers and they will be restored

lib/Target/Mips/Mips16FrameLowering.h

@@ -33,7 +33,7 @@ public:
 
   bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
                                   MachineBasicBlock::iterator MI,
-                                  const std::vector<CalleeSavedInfo> &CSI,
+                                  std::vector<CalleeSavedInfo> &CSI,
                                   const TargetRegisterInfo *TRI) const override;
 
   bool hasReservedCallFrame(const MachineFunction &MF) const override;

lib/Target/PowerPC/PPCFrameLowering.cpp

@@ -2067,7 +2067,7 @@ eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
 bool
 PPCFrameLowering::restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
                                         MachineBasicBlock::iterator MI,
-                                        const std::vector<CalleeSavedInfo> &CSI,
+                                        std::vector<CalleeSavedInfo> &CSI,
                                         const TargetRegisterInfo *TRI) const {
 
   // Currently, this function only handles SVR4 32- and 64-bit ABIs.

lib/Target/PowerPC/PPCFrameLowering.h

@@ -106,7 +106,7 @@ public:
 
   bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
                                   MachineBasicBlock::iterator MI,
-                                  const std::vector<CalleeSavedInfo> &CSI,
+                                  std::vector<CalleeSavedInfo> &CSI,
                                   const TargetRegisterInfo *TRI) const override;
 
   /// targetHandlesStackFrameRounding - Returns true if the target is

lib/Target/SystemZ/SystemZFrameLowering.cpp

@@ -220,7 +220,7 @@ spillCalleeSavedRegisters(MachineBasicBlock &MBB,
 bool SystemZFrameLowering::
 restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
                             MachineBasicBlock::iterator MBBI,
-                            const std::vector<CalleeSavedInfo> &CSI,
+                            std::vector<CalleeSavedInfo> &CSI,
                             const TargetRegisterInfo *TRI) const {
   if (CSI.empty())
     return false;

lib/Target/SystemZ/SystemZFrameLowering.h

@@ -35,7 +35,7 @@ public:
                                  const TargetRegisterInfo *TRI) const override;
   bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
                                    MachineBasicBlock::iterator MBBII,
-                                   const std::vector<CalleeSavedInfo> &CSI,
+                                   std::vector<CalleeSavedInfo> &CSI,
                                    const TargetRegisterInfo *TRI) const
     override;
   void processFunctionBeforeFrameFinalized(MachineFunction &MF,

lib/Target/X86/X86FrameLowering.cpp

@@ -1999,7 +1999,7 @@ bool X86FrameLowering::spillCalleeSavedRegisters(
 
 bool X86FrameLowering::restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
                                                MachineBasicBlock::iterator MI,
-                                        const std::vector<CalleeSavedInfo> &CSI,
+                                          std::vector<CalleeSavedInfo> &CSI,
                                           const TargetRegisterInfo *TRI) const {
   if (CSI.empty())
     return false;

lib/Target/X86/X86FrameLowering.h

@@ -89,7 +89,7 @@ public:
 
   bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
                                   MachineBasicBlock::iterator MI,
-                                  const std::vector<CalleeSavedInfo> &CSI,
+                                  std::vector<CalleeSavedInfo> &CSI,
                                   const TargetRegisterInfo *TRI) const override;
 
   bool hasFP(const MachineFunction &MF) const override;

lib/Target/XCore/XCoreFrameLowering.cpp

@@ -452,7 +452,7 @@ spillCalleeSavedRegisters(MachineBasicBlock &MBB,
 bool XCoreFrameLowering::
 restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
                             MachineBasicBlock::iterator MI,
-                            const std::vector<CalleeSavedInfo> &CSI,
+                            std::vector<CalleeSavedInfo> &CSI,
                             const TargetRegisterInfo *TRI) const{
   MachineFunction *MF = MBB.getParent();
   const TargetInstrInfo &TII = *MF->getSubtarget().getInstrInfo();

lib/Target/XCore/XCoreFrameLowering.h

@@ -38,7 +38,7 @@ namespace llvm {
                                   const TargetRegisterInfo *TRI) const override;
     bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
                                   MachineBasicBlock::iterator MI,
-                                  const std::vector<CalleeSavedInfo> &CSI,
+                                  std::vector<CalleeSavedInfo> &CSI,
                                   const TargetRegisterInfo *TRI) const override;
 
     MachineBasicBlock::iterator