[llvm] [PATCH] [Xtensa] Implement FrameLowering methods and stack operation lowering. (PR #92960)

[Andrei Safronov via llvm-commits]

================
@@ -33,10 +33,158 @@ bool XtensaFrameLowering::hasFP(const MachineFunction &MF) const {
 }
 
 void XtensaFrameLowering::emitPrologue(MachineFunction &MF,
-                                       MachineBasicBlock &MBB) const {}
+                                       MachineBasicBlock &MBB) const {
+  assert(&MBB == &MF.front() && "Shrink-wrapping not yet implemented");
+  MachineFrameInfo &MFI = MF.getFrameInfo();
+  const XtensaRegisterInfo *RegInfo = static_cast<const XtensaRegisterInfo *>(
+      MF.getSubtarget().getRegisterInfo());
+  const XtensaInstrInfo &TII =
+      *static_cast<const XtensaInstrInfo *>(MF.getSubtarget().getInstrInfo());
+  MachineBasicBlock::iterator MBBI = MBB.begin();
+  DebugLoc DL = MBBI != MBB.end() ? MBBI->getDebugLoc() : DebugLoc();
+  unsigned SP = Xtensa::SP;
+  unsigned FP = RegInfo->getFrameRegister(MF);
+  MachineModuleInfo &MMI = MF.getMMI();
+  const MCRegisterInfo *MRI = MMI.getContext().getRegisterInfo();
+
+  // First, compute final stack size.
+  uint64_t StackSize = MFI.getStackSize();
+  uint64_t PrevStackSize = StackSize;
+
+  // Round up StackSize to 16*N
+  StackSize += (16 - StackSize) & 0xf;
+
+  // No need to allocate space on the stack.
+  if (StackSize == 0 && !MFI.adjustsStack())
+    return;
+
+  // Adjust stack.
+  TII.adjustStackPtr(SP, -StackSize, MBB, MBBI);
+
+  // emit ".cfi_def_cfa_offset StackSize"
+  unsigned CFIIndex =
+      MF.addFrameInst(MCCFIInstruction::cfiDefCfaOffset(nullptr, StackSize));
+  BuildMI(MBB, MBBI, DL, TII.get(TargetOpcode::CFI_INSTRUCTION))
+      .addCFIIndex(CFIIndex);
+
+  const std::vector<CalleeSavedInfo> &CSI = MFI.getCalleeSavedInfo();
+
+  if (CSI.size()) {
+    // Find the instruction past the last instruction that saves a
+    // callee-saved register to the stack.
+    for (unsigned i = 0; i < CSI.size(); ++i)
+      ++MBBI;
+
+    // Iterate over list of callee-saved registers and emit .cfi_offset
+    // directives.
+    for (const auto &I : CSI) {
+      int64_t Offset = MFI.getObjectOffset(I.getFrameIdx());
+      Register Reg = I.getReg();
+
+      unsigned CFIIndex = MF.addFrameInst(MCCFIInstruction::createOffset(
+          nullptr, MRI->getDwarfRegNum(Reg, 1), Offset));
+      BuildMI(MBB, MBBI, DL, TII.get(TargetOpcode::CFI_INSTRUCTION))
+          .addCFIIndex(CFIIndex);
+    }
+  }
+
+  // if framepointer enabled, set it to point to the stack pointer.
+  if (hasFP(MF)) {
+    // Insert instruction "move $fp, $sp" at this location.
+    BuildMI(MBB, MBBI, DL, TII.get(Xtensa::OR), FP)
+        .addReg(SP)
+        .addReg(SP)
+        .setMIFlag(MachineInstr::FrameSetup);
+
+    // emit ".cfi_def_cfa_register $fp"
+    unsigned CFIIndex = MF.addFrameInst(MCCFIInstruction::createDefCfaRegister(
+        nullptr, MRI->getDwarfRegNum(FP, true)));
+    BuildMI(MBB, MBBI, DL, TII.get(TargetOpcode::CFI_INSTRUCTION))
+        .addCFIIndex(CFIIndex);
+  }
+
+  if (StackSize != PrevStackSize) {
+    MFI.setStackSize(StackSize);
+
+    for (int i = MFI.getObjectIndexBegin(); i < MFI.getObjectIndexEnd(); i++) {
+      if (!MFI.isDeadObjectIndex(i)) {
+        int64_t SPOffset = MFI.getObjectOffset(i);
+
+        if (SPOffset < 0)
+          MFI.setObjectOffset(i, SPOffset - StackSize + PrevStackSize);
+      }
+    }
+  }
+}
 
 void XtensaFrameLowering::emitEpilogue(MachineFunction &MF,
-                                       MachineBasicBlock &MBB) const {}
+                                       MachineBasicBlock &MBB) const {
+  MachineBasicBlock::iterator MBBI = MBB.getLastNonDebugInstr();
+  MachineFrameInfo &MFI = MF.getFrameInfo();
+  const XtensaRegisterInfo *RegInfo = static_cast<const XtensaRegisterInfo *>(
+      MF.getSubtarget().getRegisterInfo());
+  const XtensaInstrInfo &TII =
+      *static_cast<const XtensaInstrInfo *>(MF.getSubtarget().getInstrInfo());
+  DebugLoc DL = MBBI->getDebugLoc();
+  unsigned SP = Xtensa::SP;
+  unsigned FP = RegInfo->getFrameRegister(MF);
+
+  // if framepointer enabled, restore the stack pointer.
+  if (hasFP(MF)) {
+    // Find the first instruction that restores a callee-saved register.
+    MachineBasicBlock::iterator I = MBBI;
+
+    for (unsigned i = 0; i < MFI.getCalleeSavedInfo().size(); ++i)
----------------
andreisfr wrote:

Thank you very much for review. I've made some code improvements (added more comments and loop is  changed), I hope that I understand correctly your comment. Actually I used the same approach as in Mips architecture https://github.com/llvm/llvm-project/blob/57c10fa564af44a5b236bc642c540d715b04448c/llvm/lib/Target/Mips/MipsSEFrameLowering.cpp#L711 , because it is suitable for Xtensa.

https://github.com/llvm/llvm-project/pull/92960