Add the skeleton for the Mips constant island pass.

It will only be used for Mips 16 at this time.
 


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@176161 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/Mips/CMakeLists.txt

@@ -20,6 +20,7 @@ add_llvm_target(MipsCodeGen
   MipsAnalyzeImmediate.cpp
   MipsAsmPrinter.cpp
   MipsCodeEmitter.cpp
+  MipsConstantIslandPass.cpp
   MipsDelaySlotFiller.cpp
   MipsJITInfo.cpp
   MipsInstrInfo.cpp

lib/Target/Mips/Mips.h

@@ -27,6 +27,7 @@ namespace llvm {
   FunctionPass *createMipsLongBranchPass(MipsTargetMachine &TM);
   FunctionPass *createMipsJITCodeEmitterPass(MipsTargetMachine &TM,
                                              JITCodeEmitter &JCE);
+  FunctionPass *createMipsConstantIslandPass(MipsTargetMachine &tm);
 
 } // end namespace llvm;
 

lib/Target/Mips/MipsConstantIslandPass.cpp

@@ -0,0 +1,85 @@
+//===-- MipsLongBranch.cpp - Emit long branches ---------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+//
+// This pass is used to make Pc relative loads of constants.
+// For now, only Mips16 will use this. While it has the same name and
+// uses many ideas from the LLVM ARM Constant Island Pass, it's not intended
+// to reuse any of the code from the ARM version.
+//
+// Loading constants inline is expensive on Mips16 and it's in general better
+// to place the constant nearby in code space and then it can be loaded with a
+// simple 16 bit load instruction.
+//
+// The constants can be not just numbers but addresses of functions and labels.
+// This can be particularly helpful in static relocation mode for embedded
+// non linux targets.
+//
+//
+
+#define DEBUG_TYPE "mips-constant-islands"
+
+#include "Mips.h"
+#include "MCTargetDesc/MipsBaseInfo.h"
+#include "MipsTargetMachine.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/IR/Function.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/MathExtras.h"
+#include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/Target/TargetMachine.h"
+#include "llvm/Target/TargetRegisterInfo.h"
+
+using namespace llvm;
+
+namespace {
+  typedef MachineBasicBlock::iterator Iter;
+  typedef MachineBasicBlock::reverse_iterator ReverseIter;
+
+  class MipsConstantIslands : public MachineFunctionPass {
+
+  public:
+    static char ID;
+    MipsConstantIslands(TargetMachine &tm)
+      : MachineFunctionPass(ID), TM(tm),
+        TII(static_cast<const MipsInstrInfo*>(tm.getInstrInfo())),
+        IsPIC(TM.getRelocationModel() == Reloc::PIC_),
+        ABI(TM.getSubtarget<MipsSubtarget>().getTargetABI()) {}
+
+    virtual const char *getPassName() const {
+      return "Mips Constant Islands";
+    }
+
+    bool runOnMachineFunction(MachineFunction &F);
+
+  private:
+
+
+    const TargetMachine &TM;
+    const MipsInstrInfo *TII;
+    bool IsPIC;
+    unsigned ABI;
+
+  };
+
+  char MipsConstantIslands::ID = 0;
+} // end of anonymous namespace
+
+/// createMipsLongBranchPass - Returns a pass that converts branches to long
+/// branches.
+FunctionPass *llvm::createMipsConstantIslandPass(MipsTargetMachine &tm) {
+  return new MipsConstantIslands(tm);
+}
+
+bool MipsConstantIslands::runOnMachineFunction(MachineFunction &F) {
+  return true;
+}
+

lib/Target/Mips/MipsTargetMachine.cpp

@@ -116,6 +116,8 @@ bool MipsPassConfig::addPreEmitPass() {
   // NOTE: long branch has not been implemented for mips16.
   if (TM.getSubtarget<MipsSubtarget>().hasStandardEncoding())
     addPass(createMipsLongBranchPass(TM));
+  if (TM.getSubtarget<MipsSubtarget>().inMips16Mode())
+    addPass(createMipsConstantIslandPass(TM));
 
   return true;
 }