[GlobalISel] Refactor the logic to constraint registers.

Move the logic to constraint register from InstructionSelector to a
utility function. It will be required by other passes in the GlobalISel
pipeline.

llvm-svn: 290374

Author: Quentin Colombet

llvm/include/llvm/CodeGen/GlobalISel/Utils.h

@@ -0,0 +1,43 @@
+//==-- llvm/CodeGen/GlobalISel/Utils.h ---------------------------*- C++ -*-==//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+/// \file This file declares the API of helper functions used throughout the
+/// GlobalISel pipeline.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_GLOBALISEL_UTILS_H
+#define LLVM_CODEGEN_GLOBALISEL_UTILS_H
+
+namespace llvm {
+
+class MachineFunction;
+class MachineInstr;
+class MachineRegisterInfo;
+class MCInstrDesc;
+class RegisterBankInfo;
+class TargetInstrInfo;
+class TargetRegisterInfo;
+
+/// Try to constrain Reg so that it is usable by argument OpIdx of the
+/// provided MCInstrDesc \p II. If this fails, create a new virtual
+/// register in the correct class and insert a COPY before \p InsertPt.
+/// The debug location of \p InsertPt is used for the new copy.
+///
+/// \return The virtual register constrained to the right register class.
+unsigned constrainOperandRegClass(const MachineFunction &MF,
+                                  const TargetRegisterInfo &TRI,
+                                  MachineRegisterInfo &MRI,
+                                  const TargetInstrInfo &TII,
+                                  const RegisterBankInfo &RBI,
+                                  MachineInstr &InsertPt, const MCInstrDesc &II,
+                                  unsigned Reg, unsigned OpIdx);
+
+} // End namespace llvm.
+#endif

llvm/lib/CodeGen/GlobalISel/CMakeLists.txt

@@ -11,6 +11,7 @@ set(GLOBAL_ISEL_FILES
       RegBankSelect.cpp
       RegisterBank.cpp
       RegisterBankInfo.cpp
+      Utils.cpp
       )
 
 # Add GlobalISel files to the dependencies if the user wants to build it.

llvm/lib/CodeGen/GlobalISel/InstructionSelector.cpp

@@ -12,6 +12,7 @@
 
 #include "llvm/CodeGen/GlobalISel/InstructionSelector.h"
 #include "llvm/CodeGen/GlobalISel/RegisterBankInfo.h"
+#include "llvm/CodeGen/GlobalISel/Utils.h"
 #include "llvm/CodeGen/MachineInstr.h"
 #include "llvm/Target/TargetInstrInfo.h"
 #include "llvm/Target/TargetRegisterInfo.h"
@@ -39,27 +40,21 @@ bool InstructionSelector::constrainSelectedInstRegOperands(
     DEBUG(dbgs() << "Converting operand: " << MO << '\n');
     assert(MO.isReg() && "Unsupported non-reg operand");
 
+    unsigned Reg = MO.getReg();
     // Physical registers don't need to be constrained.
-    if (TRI.isPhysicalRegister(MO.getReg()))
+    if (TRI.isPhysicalRegister(Reg))
       continue;
 
     // Register operands with a value of 0 (e.g. predicate operands) don't need
     // to be constrained.
-    if (MO.getReg() == 0)
+    if (Reg == 0)
       continue;
 
-    const TargetRegisterClass *RC = TII.getRegClass(I.getDesc(), OpI, &TRI, MF);
-    assert(RC && "Selected inst should have regclass operand");
-
     // If the operand is a vreg, we should constrain its regclass, and only
     // insert COPYs if that's impossible.
-    // If the operand is a physreg, we only insert COPYs if the register class
-    // doesn't contain the register.
-    if (RBI.constrainGenericRegister(MO.getReg(), *RC, MRI))
-      continue;
-
-    DEBUG(dbgs() << "Constraining with COPYs isn't implemented yet");
-    return false;
+    // constrainOperandRegClass does that for us.
+    MO.setReg(constrainOperandRegClass(MF, TRI, MRI, TII, RBI, I, I.getDesc(),
+                                       Reg, OpI));
   }
   return true;
 }

llvm/lib/CodeGen/GlobalISel/Utils.cpp

@@ -0,0 +1,45 @@
+//===- llvm/CodeGen/GlobalISel/Utils.cpp -------------------------*- C++ -*-==//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+/// \file This file implements the utility functions used by the GlobalISel
+/// pipeline.
+//===----------------------------------------------------------------------===//
+
+#include "llvm/CodeGen/GlobalISel/Utils.h"
+#include "llvm/CodeGen/GlobalISel/RegisterBankInfo.h"
+#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/Target/TargetRegisterInfo.h"
+
+#define DEBUG_TYPE "globalisel-utils"
+
+using namespace llvm;
+
+unsigned llvm::constrainOperandRegClass(
+    const MachineFunction &MF, const TargetRegisterInfo &TRI,
+    MachineRegisterInfo &MRI, const TargetInstrInfo &TII,
+    const RegisterBankInfo &RBI, MachineInstr &InsertPt, const MCInstrDesc &II,
+    unsigned Reg, unsigned OpIdx) {
+  // Assume physical registers are properly constrained.
+  assert(TargetRegisterInfo::isVirtualRegister(Reg) &&
+         "PhysReg not implemented");
+
+  const TargetRegisterClass *RegClass = TII.getRegClass(II, OpIdx, &TRI, MF);
+
+  if (!RBI.constrainGenericRegister(Reg, *RegClass, MRI)) {
+    unsigned NewReg = MRI.createVirtualRegister(RegClass);
+    BuildMI(*InsertPt.getParent(), InsertPt, InsertPt.getDebugLoc(),
+            TII.get(TargetOpcode::COPY), NewReg)
+        .addReg(Reg);
+    return NewReg;
+  }
+
+  return Reg;
+}