[llvm] [clang] [AArch64] Stack probing for function prologues (PR #66524)

[Momchil Velikov via cfe-commits]

================
@@ -4052,3 +4193,192 @@ void AArch64FrameLowering::orderFrameObjects(
     dbgs() << "\n";
   });
 }
+
+/// Emit a loop to decrement SP until it is equal to TargetReg, with probes at
+/// least every ProbeSize bytes. Returns an iterator of the first instruction
+/// after the loop. The difference between SP and TargetReg must be an exact
+/// multiple of ProbeSize.
+MachineBasicBlock::iterator
+AArch64FrameLowering::inlineStackProbeLoopExactMultiple(
+    MachineBasicBlock::iterator MBBI, int64_t ProbeSize,
+    Register TargetReg) const {
+  MachineBasicBlock &MBB = *MBBI->getParent();
+  MachineFunction &MF = *MBB.getParent();
+  const AArch64InstrInfo *TII =
+      MF.getSubtarget<AArch64Subtarget>().getInstrInfo();
+  DebugLoc DL = MBB.findDebugLoc(MBBI);
+
+  MachineFunction::iterator MBBInsertPoint = std::next(MBB.getIterator());
+  MachineBasicBlock *LoopMBB = MF.CreateMachineBasicBlock(MBB.getBasicBlock());
+  MF.insert(MBBInsertPoint, LoopMBB);
+  MachineBasicBlock *ExitMBB = MF.CreateMachineBasicBlock(MBB.getBasicBlock());
+  MF.insert(MBBInsertPoint, ExitMBB);
+
+  // SUB SP, SP, #ProbeSize (or equivalent if ProbeSize is not encodable
+  // in SUB).
+  emitFrameOffset(*LoopMBB, LoopMBB->end(), DL, AArch64::SP, AArch64::SP,
+                  StackOffset::getFixed(-ProbeSize), TII,
+                  MachineInstr::FrameSetup);
+  // STR XZR, [SP]
+  BuildMI(*LoopMBB, LoopMBB->end(), DL, TII->get(AArch64::STRXui))
+      .addReg(AArch64::XZR)
+      .addReg(AArch64::SP)
+      .addImm(0)
+      .setMIFlags(MachineInstr::FrameSetup);
+  // CMP SP, TargetReg
+  BuildMI(*LoopMBB, LoopMBB->end(), DL, TII->get(AArch64::SUBSXrx64),
+          AArch64::XZR)
+      .addReg(AArch64::SP)
+      .addReg(TargetReg)
+      .addImm(AArch64_AM::getArithExtendImm(AArch64_AM::UXTX, 0))
+      .setMIFlags(MachineInstr::FrameSetup);
+  // B.CC Loop
+  BuildMI(*LoopMBB, LoopMBB->end(), DL, TII->get(AArch64::Bcc))
+      .addImm(AArch64CC::NE)
+      .addMBB(LoopMBB)
+      .setMIFlags(MachineInstr::FrameSetup);
+
+  LoopMBB->addSuccessor(ExitMBB);
+  LoopMBB->addSuccessor(LoopMBB);
+  // Synthesize the exit MBB.
+  ExitMBB->splice(ExitMBB->end(), &MBB, MBBI, MBB.end());
+  ExitMBB->transferSuccessorsAndUpdatePHIs(&MBB);
+  MBB.addSuccessor(LoopMBB);
+  // Update liveins.
+  recomputeLiveIns(*LoopMBB);
+  recomputeLiveIns(*ExitMBB);
+
+  return ExitMBB->begin();
+}
+
+MachineBasicBlock::iterator AArch64FrameLowering::inlineStackProbeFixed(
+    MachineBasicBlock::iterator MBBI, Register ScratchReg, int64_t FrameSize,
+    StackOffset CFAOffset) const {
+  MachineBasicBlock *MBB = MBBI->getParent();
+  MachineFunction &MF = *MBB->getParent();
+  const AArch64TargetLowering *TLI =
+      MF.getSubtarget<AArch64Subtarget>().getTargetLowering();
+  const AArch64InstrInfo *TII =
+      MF.getSubtarget<AArch64Subtarget>().getInstrInfo();
+  AArch64FunctionInfo *AFI = MF.getInfo<AArch64FunctionInfo>();
+  bool EmitAsyncCFI = AFI->needsAsyncDwarfUnwindInfo(MF);
+  bool HasFP = hasFP(MF);
+
+  DebugLoc DL;
+  int64_t ProbeSize = TLI->getStackProbeSize(MF);
+  int64_t NumBlocks = FrameSize / ProbeSize;
+  int64_t ResidualSize = FrameSize % ProbeSize;
+
+  LLVM_DEBUG(dbgs() << "Stack probing: total " << FrameSize << " bytes, "
+                    << NumBlocks << " blocks of " << ProbeSize
+                    << " bytes, plus " << ResidualSize << " bytes\n");
+
+  // Decrement SP by NumBlock * ProbeSize bytes, with either unrolled or
+  // ordinary loop.
+  if (NumBlocks <= AArch64::StackProbeMaxLoopUnroll) {
+    for (int i = 0; i < NumBlocks; ++i) {
+      // SUB SP, SP, #FrameSize (or equivalent if FrameSize is not
----------------
momchil-velikov wrote:

Wrong comment (code is OK): ProbeSize, not FrameSize.

https://github.com/llvm/llvm-project/pull/66524