[SystemZ] Add back end

This adds the actual lib/Target/SystemZ target files necessary to
implement the SystemZ target.  Note that at this point, the target
cannot yet be built since the configure bits are missing.  Those
will be provided shortly by a follow-on patch.

This version of the patch incorporates feedback from reviews by
Chris Lattner and Anton Korobeynikov.  Thanks to all reviewers!

Patch by Richard Sandiford.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181203 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 116 insertions, 0 deletions

diff --git a/lib/Target/SystemZ/SystemZMCInstLower.cpp b/lib/Target/SystemZ/SystemZMCInstLower.cpp
new file mode 100644
index 0000000000..5d833213e6
--- /dev/null
+++ b/lib/Target/SystemZ/SystemZMCInstLower.cpp
@@ -0,0 +1,116 @@
+//===-- SystemZMCInstLower.cpp - Lower MachineInstr to MCInst -------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "SystemZMCInstLower.h"
+#include "SystemZAsmPrinter.h"
+#include "llvm/MC/MCExpr.h"
+#include "llvm/MC/MCStreamer.h"
+#include "llvm/Target/Mangler.h"
+
+using namespace llvm;
+
+// Where relaxable pairs of reloc-generating instructions exist,
+// we tend to use the longest form by default, since that produces
+// correct assembly in cases where no relaxation is performed.
+// If Opcode is one such instruction, return the opcode for the
+// shortest possible form instead, otherwise return Opcode itself.
+static unsigned getShortenedInstr(unsigned Opcode) {
+  switch (Opcode) {
+  case SystemZ::BRCL:  return SystemZ::BRC;
+  case SystemZ::JG:    return SystemZ::J;
+  case SystemZ::BRASL: return SystemZ::BRAS;
+  }
+  return Opcode;
+}
+
+// Return the VK_* enumeration for MachineOperand target flags Flags.
+static MCSymbolRefExpr::VariantKind getVariantKind(unsigned Flags) {
+  switch (Flags & SystemZII::MO_SYMBOL_MODIFIER) {
+    case 0:
+      return MCSymbolRefExpr::VK_None;
+    case SystemZII::MO_GOT:
+      return MCSymbolRefExpr::VK_GOT;
+  }
+  llvm_unreachable("Unrecognised MO_ACCESS_MODEL");
+}
+
+SystemZMCInstLower::SystemZMCInstLower(Mangler *mang, MCContext &ctx,
+                                       SystemZAsmPrinter &asmprinter)
+  : Mang(mang), Ctx(ctx), AsmPrinter(asmprinter) {}
+
+MCOperand SystemZMCInstLower::lowerSymbolOperand(const MachineOperand &MO,
+                                                 const MCSymbol *Symbol,
+                                                 int64_t Offset) const {
+  MCSymbolRefExpr::VariantKind Kind = getVariantKind(MO.getTargetFlags());
+  const MCExpr *Expr = MCSymbolRefExpr::Create(Symbol, Kind, Ctx);
+  if (Offset) {
+    const MCExpr *OffsetExpr = MCConstantExpr::Create(Offset, Ctx);
+    Expr = MCBinaryExpr::CreateAdd(Expr, OffsetExpr, Ctx);
+  }
+  return MCOperand::CreateExpr(Expr);
+}
+
+MCOperand SystemZMCInstLower::lowerOperand(const MachineOperand &MO) const {
+  switch (MO.getType()) {
+  default:
+    llvm_unreachable("unknown operand type");
+
+  case MachineOperand::MO_Register:
+    // Ignore all implicit register operands.
+    if (MO.isImplicit())
+      return MCOperand();
+    return MCOperand::CreateReg(MO.getReg());
+
+  case MachineOperand::MO_Immediate:
+    return MCOperand::CreateImm(MO.getImm());
+
+  case MachineOperand::MO_MachineBasicBlock:
+    return lowerSymbolOperand(MO, MO.getMBB()->getSymbol(),
+                              /* MO has no offset field */0);
+
+  case MachineOperand::MO_GlobalAddress:
+    return lowerSymbolOperand(MO, Mang->getSymbol(MO.getGlobal()),
+                              MO.getOffset());
+
+  case MachineOperand::MO_ExternalSymbol: {
+    StringRef Name = MO.getSymbolName();
+    return lowerSymbolOperand(MO, AsmPrinter.GetExternalSymbolSymbol(Name),
+                              MO.getOffset());
+  }
+
+  case MachineOperand::MO_JumpTableIndex:
+    return lowerSymbolOperand(MO, AsmPrinter.GetJTISymbol(MO.getIndex()),
+                              /* MO has no offset field */0);
+
+  case MachineOperand::MO_ConstantPoolIndex:
+    return lowerSymbolOperand(MO, AsmPrinter.GetCPISymbol(MO.getIndex()),
+                              MO.getOffset());
+
+  case MachineOperand::MO_BlockAddress: {
+    const BlockAddress *BA = MO.getBlockAddress();
+    return lowerSymbolOperand(MO, AsmPrinter.GetBlockAddressSymbol(BA),
+                              MO.getOffset());
+  }
+  }
+}
+
+void SystemZMCInstLower::lower(const MachineInstr *MI, MCInst &OutMI) const {
+  unsigned Opcode = MI->getOpcode();
+  // When emitting binary code, start with the shortest form of an instruction
+  // and then relax it where necessary.
+  if (!AsmPrinter.OutStreamer.hasRawTextSupport())
+    Opcode = getShortenedInstr(Opcode);
+  OutMI.setOpcode(Opcode);
+  for (unsigned I = 0, E = MI->getNumOperands(); I != E; ++I) {
+    const MachineOperand &MO = MI->getOperand(I);
+    MCOperand MCOp = lowerOperand(MO);
+    if (MCOp.isValid())
+      OutMI.addOperand(MCOp);
+  }
+}