[Hexagon] Fix debug information for local objects

- Isolate the check for the existence of a stack frame into hasFP.
- Implement getFrameIndexReference for DWARF address computation.
- Use getFrameIndexReference for offset computation in eliminateFrameIndex.
- Preserve debug information for dynamically allocated stack objects.
- Prefer FP to access local objects at -O0.
- Add experimental code to skip allocframe when not strictly necessary
  (disabled by default).

llvm-svn: 250718

1 files changed, 13 insertions, 68 deletions

diff --git a/llvm/lib/Target/Hexagon/HexagonRegisterInfo.cpp b/llvm/lib/Target/Hexagon/HexagonRegisterInfo.cpp
index 8f5e8ded1a5..e32ca649312 100644
--- a/llvm/lib/Target/Hexagon/HexagonRegisterInfo.cpp
+++ b/llvm/lib/Target/Hexagon/HexagonRegisterInfo.cpp
@@ -120,62 +120,21 @@ void HexagonRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
   assert(SPAdj == 0 && "Unexpected");
 
   MachineInstr &MI = *II;
-
   MachineBasicBlock &MB = *MI.getParent();
   MachineFunction &MF = *MB.getParent();
-  MachineFrameInfo &MFI = *MF.getFrameInfo();
-  auto &HST = static_cast<const HexagonSubtarget&>(MF.getSubtarget());
+  auto &HST = MF.getSubtarget<HexagonSubtarget>();
   auto &HII = *HST.getInstrInfo();
   auto &HFI = *HST.getFrameLowering();
 
+  unsigned BP = 0;
   int FI = MI.getOperand(FIOp).getIndex();
-  int Offset = MFI.getObjectOffset(FI) + MI.getOperand(FIOp+1).getImm();
-  bool HasAlloca = MFI.hasVarSizedObjects();
-  bool HasAlign = needsStackRealignment(MF);
-
-  // XXX: Fixed objects cannot be accessed through SP if there are aligned
-  // objects in the local frame, or if there are dynamically allocated objects.
-  // In such cases, there has to be FP available.
-  if (!HFI.hasFP(MF)) {
-    assert(!HasAlloca && !HasAlign && "This function must have frame pointer");
-    // We will not reserve space on the stack for the lr and fp registers.
-    Offset -= 8;
-  }
-
-  unsigned SP = getStackRegister(), FP = getFrameRegister();
-  unsigned AP = 0;
-  if (MachineInstr *AI = HFI.getAlignaInstr(MF))
-    AP = AI->getOperand(0).getReg();
-  unsigned FrameSize = MFI.getStackSize();
-
-  // Special handling of dbg_value instructions and INLINEASM.
-  if (MI.isDebugValue() || MI.isInlineAsm()) {
-    MI.getOperand(FIOp).ChangeToRegister(SP, false /*isDef*/);
-    MI.getOperand(FIOp+1).ChangeToImmediate(Offset+FrameSize);
-    return;
-  }
-
-  bool UseFP = false, UseAP = false;  // Default: use SP.
-  if (MFI.isFixedObjectIndex(FI) || MFI.isObjectPreAllocated(FI)) {
-    UseFP = HasAlloca || HasAlign;
-  } else {
-    if (HasAlloca) {
-      if (HasAlign)
-        UseAP = true;
-      else
-        UseFP = true;
-    }
-  }
+  // Select the base pointer (BP) and calculate the actual offset from BP
+  // to the beginning of the object at index FI.
+  int Offset = HFI.getFrameIndexReference(MF, FI, BP);
+  // Add the offset from the instruction.
+  int RealOffset = Offset + MI.getOperand(FIOp+1).getImm();
 
   unsigned Opc = MI.getOpcode();
-  bool ValidSP = HII.isValidOffset(Opc, FrameSize+Offset);
-  bool ValidFP = HII.isValidOffset(Opc, Offset);
-
-  // Calculate the actual offset in the instruction.
-  int64_t RealOffset = Offset;
-  if (!UseFP && !UseAP)
-    RealOffset = FrameSize+Offset;
-
   switch (Opc) {
     case Hexagon::TFR_FIA:
       MI.setDesc(HII.get(Hexagon::A2_addi));
@@ -188,20 +147,7 @@ void HexagonRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
       break;
   }
 
-  unsigned BP = 0;
-  bool Valid = false;
-  if (UseFP) {
-    BP = FP;
-    Valid = ValidFP;
-  } else if (UseAP) {
-    BP = AP;
-    Valid = ValidFP;
-  } else {
-    BP = SP;
-    Valid = ValidSP;
-  }
-
-  if (Valid) {
+  if (HII.isValidOffset(Opc, RealOffset)) {
     MI.getOperand(FIOp).ChangeToRegister(BP, false);
     MI.getOperand(FIOp+1).ChangeToImmediate(RealOffset);
     return;
@@ -227,8 +173,8 @@ unsigned HexagonRegisterInfo::getFrameRegister(const MachineFunction
                                                &MF) const {
   const HexagonFrameLowering *TFI = getFrameLowering(MF);
   if (TFI->hasFP(MF))
-    return Hexagon::R30;
-  return Hexagon::R29;
+    return getFrameRegister();
+  return getStackRegister();
 }
 
 
@@ -242,10 +188,9 @@ unsigned HexagonRegisterInfo::getStackRegister() const {
 }
 
 
-bool
-HexagonRegisterInfo::useFPForScavengingIndex(const MachineFunction &MF) const {
-  const HexagonFrameLowering *TFI = getFrameLowering(MF);
-  return TFI->hasFP(MF);
+bool HexagonRegisterInfo::useFPForScavengingIndex(const MachineFunction &MF)
+      const {
+  return MF.getSubtarget<HexagonSubtarget>().getFrameLowering()->hasFP(MF);
 }