[llvm] [Xtensa] Initial codegen support from IR (PR #78548)

[Matt Arsenault via llvm-commits]

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+//===- XtensaRegisterInfo.cpp - Xtensa Register Information ---------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains the Xtensa implementation of the TargetRegisterInfo class.
+//
+//===----------------------------------------------------------------------===//
+
+#include "XtensaRegisterInfo.h"
+#include "XtensaInstrInfo.h"
+#include "XtensaSubtarget.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/raw_ostream.h"
+
+#define DEBUG_TYPE "xtensa-reg-info"
+
+#define GET_REGINFO_TARGET_DESC
+#include "XtensaGenRegisterInfo.inc"
+
+using namespace llvm;
+
+XtensaRegisterInfo::XtensaRegisterInfo(const XtensaSubtarget &STI)
+    : XtensaGenRegisterInfo(Xtensa::A0), Subtarget(STI) {}
+
+const uint16_t *
+XtensaRegisterInfo::getCalleeSavedRegs(const MachineFunction *MF) const {
+  // Calling convention is not implemented yet
+  return nullptr;
+}
+
+const uint32_t *
+XtensaRegisterInfo::getCallPreservedMask(const MachineFunction &MF,
+                                         CallingConv::ID) const {
+  // Calling convention is not implemented yet
+  return nullptr;
+}
+
+BitVector XtensaRegisterInfo::getReservedRegs(const MachineFunction &MF) const {
+  BitVector Reserved(getNumRegs());
+  const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
+
+  Reserved.set(Xtensa::A0);
+  if (TFI->hasFP(MF)) {
+    // Reserve frame pointer.
+    Reserved.set(getFrameRegister(MF));
+  }
+
+  // Reserve stack pointer.
+  Reserved.set(Xtensa::SP);
+  return Reserved;
+}
+
+bool XtensaRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
+                                             int SPAdj, unsigned FIOperandNum,
+                                             RegScavenger *RS) const {
+  report_fatal_error("Eliminate frame index not supported yet");
+  return false;
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arsenm wrote:

dead return 

https://github.com/llvm/llvm-project/pull/78548