First stage of call lowering for Mips fast-isel

Summary:
This has most of what is needed for mips fast-isel call lowering for O32.
What is missing I will add on the next patch because this patch is already too large.
It should not be doing anything wrong but it will punt on some cases that it is basically
capable of doing.

The mechanism is there for parameters to be passed on the stack but I have not enabled it because it serves as a way for now to prevent some of the strange cases of O32 register passing that I have not fully checked yet and have some issues.

The Mips O32 abi rules are very complicated as far how data is passed in floating and integer registers.

However there is a way to think about this all very simply and this implementation reflects that.

Basically, the ABI rules are written as if everything is passed on the stack and aligned as such.
Once that is conceptually done, it is nearly trivial to reassign those locations to registers and
then all the complexity disappears.

So I have told tablegen that all the data is passed on the stack and during the lowering I fix
this by assigning to registers as per the ABI doc.

This has been my approach and you can line up what I did with the ABI document and see 1 to 1 what
is going on.



Test Plan: callabi.ll

Reviewers: dsanders

Reviewed By: dsanders

Subscribers: jholewinski, echristo, ahatanak, llvm-commits, rfuhler

Differential Revision: http://reviews.llvm.org/D5714

llvm-svn: 221948

3 files changed, 319 insertions, 2 deletions

diff --git a/llvm/lib/Target/Mips/MipsCallingConv.td b/llvm/lib/Target/Mips/MipsCallingConv.td
index c6706a8e8fb..7318de26da2 100644
--- a/llvm/lib/Target/Mips/MipsCallingConv.td
+++ b/llvm/lib/Target/Mips/MipsCallingConv.td
@@ -51,6 +51,19 @@ def RetCC_F128 : CallingConv<[
 // Mips O32 Calling Convention
 //===----------------------------------------------------------------------===//
 
+def CC_MipsO32 : CallingConv<[
+  // Promote i8/i16 arguments to i32.
+  CCIfType<[i1, i8, i16], CCPromoteToType<i32>>,
+
+  // Integer values get stored in stack slots that are 4 bytes in
+  // size and 4-byte aligned.
+  CCIfType<[i32, f32], CCAssignToStack<4, 4>>,
+
+  // Integer values get stored in stack slots that are 8 bytes in
+  // size and 8-byte aligned.
+  CCIfType<[f64], CCAssignToStack<8, 8>>
+]>;
+
 // Only the return rules are defined here for O32. The rules for argument
 // passing are defined in MipsISelLowering.cpp.
 def RetCC_MipsO32 : CallingConv<[
diff --git a/llvm/lib/Target/Mips/MipsFastISel.cpp b/llvm/lib/Target/Mips/MipsFastISel.cpp
index 97682d8ae9e..ad31ef8ea4d 100644
--- a/llvm/lib/Target/Mips/MipsFastISel.cpp
+++ b/llvm/lib/Target/Mips/MipsFastISel.cpp
@@ -8,6 +8,7 @@
 #include "llvm/IR/GlobalVariable.h"
 #include "llvm/Target/TargetInstrInfo.h"
 #include "llvm/Target/TargetLibraryInfo.h"
+#include "MipsCCState.h"
 #include "MipsRegisterInfo.h"
 #include "MipsISelLowering.h"
 #include "MipsMachineFunction.h"
@@ -68,6 +69,8 @@ class MipsFastISel final : public FastISel {
   // Convenience variables to avoid some queries.
   LLVMContext *Context;
 
+  bool fastLowerCall(CallLoweringInfo &CLI) override;
+
   bool TargetSupported;
   bool UnsupportedFPMode; // To allow fast-isel to proceed and just not handle
   // floating point but not reject doing fast-isel in other
@@ -87,17 +90,20 @@ private:
   bool selectIntExt(const Instruction *I);
 
   // Utility helper routines.
-
   bool isTypeLegal(Type *Ty, MVT &VT);
   bool isLoadTypeLegal(Type *Ty, MVT &VT);
   bool computeAddress(const Value *Obj, Address &Addr);
+  bool computeCallAddress(const Value *V, Address &Addr);
 
   // Emit helper routines.
   bool emitCmp(unsigned DestReg, const CmpInst *CI);
   bool emitLoad(MVT VT, unsigned &ResultReg, Address &Addr,
                 unsigned Alignment = 0);
+  bool emitStore(MVT VT, unsigned SrcReg, Address Addr,
+                 MachineMemOperand *MMO = nullptr);
   bool emitStore(MVT VT, unsigned SrcReg, Address &Addr,
                  unsigned Alignment = 0);
+  unsigned emitIntExt(MVT SrcVT, unsigned SrcReg, MVT DestVT, bool isZExt);
   bool emitIntExt(MVT SrcVT, unsigned SrcReg, MVT DestVT, unsigned DestReg,
 
                   bool IsZExt);
@@ -140,9 +146,15 @@ private:
     return 0;
   }
 
+  // Call handling routines.
+private:
+  CCAssignFn *CCAssignFnForCall(CallingConv::ID CC) const;
+  bool processCallArgs(CallLoweringInfo &CLI, SmallVectorImpl<MVT> &ArgVTs,
+                       unsigned &NumBytes);
+  bool finishCall(CallLoweringInfo &CLI, MVT RetVT, unsigned NumBytes);
+
 public:
   // Backend specific FastISel code.
-
   explicit MipsFastISel(FunctionLoweringInfo &funcInfo,
                         const TargetLibraryInfo *libInfo)
       : FastISel(funcInfo, libInfo),
@@ -166,6 +178,28 @@ public:
 };
 } // end anonymous namespace.
 
+static bool CC_Mips(unsigned ValNo, MVT ValVT, MVT LocVT,
+                    CCValAssign::LocInfo LocInfo, ISD::ArgFlagsTy ArgFlags,
+                    CCState &State) __attribute__((unused));
+
+static bool CC_MipsO32_FP32(unsigned ValNo, MVT ValVT, MVT LocVT,
+                            CCValAssign::LocInfo LocInfo,
+                            ISD::ArgFlagsTy ArgFlags, CCState &State) {
+  llvm_unreachable("should not be called");
+}
+
+bool CC_MipsO32_FP64(unsigned ValNo, MVT ValVT, MVT LocVT,
+                     CCValAssign::LocInfo LocInfo, ISD::ArgFlagsTy ArgFlags,
+                     CCState &State) {
+  llvm_unreachable("should not be called");
+}
+
+#include "MipsGenCallingConv.inc"
+
+CCAssignFn *MipsFastISel::CCAssignFnForCall(CallingConv::ID CC) const {
+  return CC_MipsO32;
+}
+
 unsigned MipsFastISel::materializeInt(const Constant *C, MVT VT) {
   if (VT != MVT::i32 && VT != MVT::i16 && VT != MVT::i8 && VT != MVT::i1)
     return 0;
@@ -284,6 +318,19 @@ bool MipsFastISel::computeAddress(const Value *Obj, Address &Addr) {
   return Addr.getReg() != 0;
 }
 
+bool MipsFastISel::computeCallAddress(const Value *V, Address &Addr) {
+  const GlobalValue *GV = dyn_cast<GlobalValue>(V);
+  if (GV && isa<Function>(GV) && dyn_cast<Function>(GV)->isIntrinsic())
+    return false;
+  if (!GV)
+    return false;
+  if (const GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
+    Addr.setGlobalValue(GV);
+    return true;
+  }
+  return false;
+}
+
 bool MipsFastISel::isTypeLegal(Type *Ty, MVT &VT) {
   EVT evt = TLI.getValueType(Ty, true);
   // Only handle simple types.
@@ -694,6 +741,250 @@ bool MipsFastISel::selectFPToInt(const Instruction *I, bool IsSigned) {
   return true;
 }
 //
+bool MipsFastISel::processCallArgs(CallLoweringInfo &CLI,
+                                   SmallVectorImpl<MVT> &OutVTs,
+                                   unsigned &NumBytes) {
+  CallingConv::ID CC = CLI.CallConv;
+  SmallVector<CCValAssign, 16> ArgLocs;
+  CCState CCInfo(CC, false, *FuncInfo.MF, ArgLocs, *Context);
+  CCInfo.AnalyzeCallOperands(OutVTs, CLI.OutFlags, CCAssignFnForCall(CC));
+  // Get a count of how many bytes are to be pushed on the stack.
+  NumBytes = CCInfo.getNextStackOffset();
+  // This is the minimum argument area used for A0-A3.
+  if (NumBytes < 16)
+    NumBytes = 16;
+
+  emitInst(Mips::ADJCALLSTACKDOWN).addImm(16);
+  // Process the args.
+  MVT firstMVT;
+  for (unsigned i = 0, e = ArgLocs.size(); i != e; ++i) {
+    CCValAssign &VA = ArgLocs[i];
+    const Value *ArgVal = CLI.OutVals[VA.getValNo()];
+    MVT ArgVT = OutVTs[VA.getValNo()];
+
+    if (i == 0) {
+      firstMVT = ArgVT;
+      if (ArgVT == MVT::f32) {
+        VA.convertToReg(Mips::F12);
+      } else if (ArgVT == MVT::f64) {
+        VA.convertToReg(Mips::D6);
+      }
+    } else if (i == 1) {
+      if ((firstMVT == MVT::f32) || (firstMVT == MVT::f64)) {
+        if (ArgVT == MVT::f32) {
+          VA.convertToReg(Mips::F14);
+        } else if (ArgVT == MVT::f64) {
+          VA.convertToReg(Mips::D7);
+        }
+      }
+    }
+    if (((ArgVT == MVT::i32) || (ArgVT == MVT::f32)) && VA.isMemLoc()) {
+      switch (VA.getLocMemOffset()) {
+      case 0:
+        VA.convertToReg(Mips::A0);
+        break;
+      case 4:
+        VA.convertToReg(Mips::A1);
+        break;
+      case 8:
+        VA.convertToReg(Mips::A2);
+        break;
+      case 12:
+        VA.convertToReg(Mips::A3);
+        break;
+      default:
+        break;
+      }
+    }
+    unsigned ArgReg = getRegForValue(ArgVal);
+    if (!ArgReg)
+      return false;
+
+    // Handle arg promotion: SExt, ZExt, AExt.
+    switch (VA.getLocInfo()) {
+    case CCValAssign::Full:
+      break;
+    case CCValAssign::AExt:
+    case CCValAssign::SExt: {
+      MVT DestVT = VA.getLocVT();
+      MVT SrcVT = ArgVT;
+      ArgReg = emitIntExt(SrcVT, ArgReg, DestVT, /*isZExt=*/false);
+      if (!ArgReg)
+        return false;
+      break;
+    }
+    case CCValAssign::ZExt: {
+      MVT DestVT = VA.getLocVT();
+      MVT SrcVT = ArgVT;
+      ArgReg = emitIntExt(SrcVT, ArgReg, DestVT, /*isZExt=*/true);
+      if (!ArgReg)
+        return false;
+      break;
+    }
+    default:
+      llvm_unreachable("Unknown arg promotion!");
+    }
+
+    // Now copy/store arg to correct locations.
+    if (VA.isRegLoc() && !VA.needsCustom()) {
+      BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DbgLoc,
+              TII.get(TargetOpcode::COPY), VA.getLocReg()).addReg(ArgReg);
+      CLI.OutRegs.push_back(VA.getLocReg());
+    } else if (VA.needsCustom()) {
+      llvm_unreachable("Mips does not use custom args.");
+      return false;
+    } else {
+      //
+      // FIXME: This path will currently return false. It was copied
+      // from the AArch64 port and should be essentially fine for Mips too.
+      // The work to finish up this path will be done in a follow-on patch.
+      //
+      assert(VA.isMemLoc() && "Assuming store on stack.");
+      // Don't emit stores for undef values.
+      if (isa<UndefValue>(ArgVal))
+        continue;
+
+      // Need to store on the stack.
+      // FIXME: This alignment is incorrect but this path is disabled
+      // for now (will return false). We need to determine the right alignment
+      // based on the normal alignment for the underlying machine type.
+      //
+      unsigned ArgSize = RoundUpToAlignment(ArgVT.getSizeInBits(), 4);
+
+      unsigned BEAlign = 0;
+      if (ArgSize < 8 && !Subtarget->isLittle())
+        BEAlign = 8 - ArgSize;
+
+      Address Addr;
+      Addr.setKind(Address::RegBase);
+      Addr.setReg(Mips::SP);
+      Addr.setOffset(VA.getLocMemOffset() + BEAlign);
+
+      unsigned Alignment = DL.getABITypeAlignment(ArgVal->getType());
+      MachineMemOperand *MMO = FuncInfo.MF->getMachineMemOperand(
+          MachinePointerInfo::getStack(Addr.getOffset()),
+          MachineMemOperand::MOStore, ArgVT.getStoreSize(), Alignment);
+      (void)(MMO);
+      // if (!emitStore(ArgVT, ArgReg, Addr, MMO))
+      return false; // can't store on the stack yet.
+    }
+  }
+
+  return true;
+}
+
+bool MipsFastISel::finishCall(CallLoweringInfo &CLI, MVT RetVT,
+                              unsigned NumBytes) {
+  CallingConv::ID CC = CLI.CallConv;
+  emitInst(Mips::ADJCALLSTACKUP).addImm(16);
+  if (RetVT != MVT::isVoid) {
+    SmallVector<CCValAssign, 16> RVLocs;
+    CCState CCInfo(CC, false, *FuncInfo.MF, RVLocs, *Context);
+    CCInfo.AnalyzeCallResult(RetVT, RetCC_Mips);
+
+    // Only handle a single return value.
+    if (RVLocs.size() != 1)
+      return false;
+    // Copy all of the result registers out of their specified physreg.
+    MVT CopyVT = RVLocs[0].getValVT();
+    // Special handling for extended integers.
+    if (RetVT == MVT::i1 || RetVT == MVT::i8 || RetVT == MVT::i16)
+      CopyVT = MVT::i32;
+
+    unsigned ResultReg = createResultReg(TLI.getRegClassFor(CopyVT));
+    BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DbgLoc,
+            TII.get(TargetOpcode::COPY),
+            ResultReg).addReg(RVLocs[0].getLocReg());
+    CLI.InRegs.push_back(RVLocs[0].getLocReg());
+
+    CLI.ResultReg = ResultReg;
+    CLI.NumResultRegs = 1;
+  }
+  return true;
+}
+
+bool MipsFastISel::fastLowerCall(CallLoweringInfo &CLI) {
+  CallingConv::ID CC = CLI.CallConv;
+  bool IsTailCall = CLI.IsTailCall;
+  bool IsVarArg = CLI.IsVarArg;
+  const Value *Callee = CLI.Callee;
+  // const char *SymName = CLI.SymName;
+
+  // Allow SelectionDAG isel to handle tail calls.
+  if (IsTailCall)
+    return false;
+
+  // Let SDISel handle vararg functions.
+  if (IsVarArg)
+    return false;
+
+  // FIXME: Only handle *simple* calls for now.
+  MVT RetVT;
+  if (CLI.RetTy->isVoidTy())
+    RetVT = MVT::isVoid;
+  else if (!isTypeLegal(CLI.RetTy, RetVT))
+    return false;
+
+  for (auto Flag : CLI.OutFlags)
+    if (Flag.isInReg() || Flag.isSRet() || Flag.isNest() || Flag.isByVal())
+      return false;
+
+  // Set up the argument vectors.
+  SmallVector<MVT, 16> OutVTs;
+  OutVTs.reserve(CLI.OutVals.size());
+
+  for (auto *Val : CLI.OutVals) {
+    MVT VT;
+    if (!isTypeLegal(Val->getType(), VT) &&
+        !(VT == MVT::i1 || VT == MVT::i8 || VT == MVT::i16))
+      return false;
+
+    // We don't handle vector parameters yet.
+    if (VT.isVector() || VT.getSizeInBits() > 64)
+      return false;
+
+    OutVTs.push_back(VT);
+  }
+
+  Address Addr;
+  if (!computeCallAddress(Callee, Addr))
+    return false;
+
+  // Handle the arguments now that we've gotten them.
+  unsigned NumBytes;
+  if (!processCallArgs(CLI, OutVTs, NumBytes))
+    return false;
+
+  // Issue the call.
+  unsigned DestAddress = materializeGV(Addr.getGlobalValue(), MVT::i32);
+  emitInst(TargetOpcode::COPY, Mips::T9).addReg(DestAddress);
+  MachineInstrBuilder MIB =
+      BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DbgLoc, TII.get(Mips::JALR),
+              Mips::RA).addReg(Mips::T9);
+
+  // Add implicit physical register uses to the call.
+  for (auto Reg : CLI.OutRegs)
+    MIB.addReg(Reg, RegState::Implicit);
+
+  // Add a register mask with the call-preserved registers.
+  // Proper defs for return values will be added by setPhysRegsDeadExcept().
+  MIB.addRegMask(TRI.getCallPreservedMask(CC));
+
+  CLI.Call = MIB;
+
+  // Add implicit physical register uses to the call.
+  for (auto Reg : CLI.OutRegs)
+    MIB.addReg(Reg, RegState::Implicit);
+
+  // Add a register mask with the call-preserved registers.  Proper
+  // defs for return values will be added by setPhysRegsDeadExcept().
+  MIB.addRegMask(TRI.getCallPreservedMask(CC));
+
+  CLI.Call = MIB;
+  // Finish off the call including any return values.
+  return finishCall(CLI, RetVT, NumBytes);
+}
+
 bool MipsFastISel::selectRet(const Instruction *I) {
   const ReturnInst *Ret = cast<ReturnInst>(I);
 
@@ -812,6 +1103,7 @@ bool MipsFastISel::emitIntZExt(MVT SrcVT, unsigned SrcReg, MVT DestVT,
     break;
   case MVT::i16:
     emitInst(Mips::ANDi, DestReg).addReg(SrcReg).addImm(0xffff);
+    break;
   }
   return true;
 }
@@ -822,6 +1114,13 @@ bool MipsFastISel::emitIntExt(MVT SrcVT, unsigned SrcReg, MVT DestVT,
     return emitIntZExt(SrcVT, SrcReg, DestVT, DestReg);
   return emitIntSExt(SrcVT, SrcReg, DestVT, DestReg);
 }
+
+unsigned MipsFastISel::emitIntExt(MVT SrcVT, unsigned SrcReg, MVT DestVT,
+                                  bool isZExt) {
+  unsigned DestReg = createResultReg(&Mips::GPR32RegClass);
+  return emitIntExt(SrcVT, SrcReg, DestVT, DestReg, isZExt);
+}
+
 bool MipsFastISel::fastSelectInstruction(const Instruction *I) {
   if (!TargetSupported)
     return false;
diff --git a/llvm/lib/Target/Mips/MipsISelLowering.cpp b/llvm/lib/Target/Mips/MipsISelLowering.cpp
index a7117adbdeb..08519836fd5 100644
--- a/llvm/lib/Target/Mips/MipsISelLowering.cpp
+++ b/llvm/lib/Target/Mips/MipsISelLowering.cpp
@@ -2356,6 +2356,11 @@ static bool CC_MipsO32_FP64(unsigned ValNo, MVT ValVT,
   return CC_MipsO32(ValNo, ValVT, LocVT, LocInfo, ArgFlags, State, F64Regs);
 }
 
+static bool CC_MipsO32(unsigned ValNo, MVT ValVT,
+                   MVT LocVT, CCValAssign::LocInfo LocInfo,
+                   ISD::ArgFlagsTy ArgFlags, CCState &State)
+__attribute__((unused));
+
 #include "MipsGenCallingConv.inc"
 
 //===----------------------------------------------------------------------===//