[SelectionDAG] Enable target specific vector scalarization of calls and returns

By target hookifying getRegisterType, getNumRegisters, getVectorBreakdown,
backends can request that LLVM to scalarize vector types for calls
and returns.

The MIPS vector ABI requires that vector arguments and returns are passed in
integer registers. With SelectionDAG's new hooks, the MIPS backend can now
handle LLVM-IR with vector types in calls and returns. E.g.
'call @foo(<4 x i32> %4)'.

Previously these cases would be scalarized for the MIPS O32/N32/N64 ABI for
calls and returns if vector types were not legal. If vector types were legal,
a single 128bit vector argument would be assigned to a single 32 bit / 64 bit
integer register.

By teaching the MIPS backend to inspect the original types, it can now
implement the MIPS vector ABI which requires a particular method of
scalarizing vectors.

Previously, the MIPS backend relied on clang to scalarize types such as "call
@foo(<4 x float> %a) into "call @foo(i32 inreg %1, i32 inreg %2, i32 inreg %3,
i32 inreg %4)".

This patch enables the MIPS backend to take either form for vector types.

Reviewers: zoran.jovanovic, jaydeep, vkalintiris, slthakur

Differential Revision: https://reviews.llvm.org/D27845

llvm-svn: 299766

6 files changed, 198 insertions, 15 deletions

diff --git a/llvm/lib/Target/Mips/MipsCCState.cpp b/llvm/lib/Target/Mips/MipsCCState.cpp
index 7af988c1f64..62ff99c7816 100644
--- a/llvm/lib/Target/Mips/MipsCCState.cpp
+++ b/llvm/lib/Target/Mips/MipsCCState.cpp
@@ -54,6 +54,22 @@ static bool originalTypeIsF128(Type *Ty, const SDNode *CallNode) {
   return (ES && Ty->isIntegerTy(128) && isF128SoftLibCall(ES->getSymbol()));
 }
 
+/// Return true if the original type was vXfXX.
+static bool originalEVTTypeIsVectorFloat(EVT Ty) {
+  if (Ty.isVector() && Ty.getVectorElementType().isFloatingPoint())
+    return true;
+
+  return false;
+}
+
+/// Return true if the original type was vXfXX / vXfXX.
+static bool originalTypeIsVectorFloat(Type * Ty) {
+  if (Ty->isVectorTy() && Ty->isFPOrFPVectorTy())
+    return true;
+
+  return false;
+}
+
 MipsCCState::SpecialCallingConvType
 MipsCCState::getSpecialCallingConvForCallee(const SDNode *Callee,
                                             const MipsSubtarget &Subtarget) {
@@ -81,8 +97,8 @@ void MipsCCState::PreAnalyzeCallResultForF128(
   }
 }
 
-/// Identify lowered values that originated from f128 arguments and record
-/// this for use by RetCC_MipsN.
+/// Identify lowered values that originated from f128 or float arguments and
+/// record this for use by RetCC_MipsN.
 void MipsCCState::PreAnalyzeReturnForF128(
     const SmallVectorImpl<ISD::OutputArg> &Outs) {
   const MachineFunction &MF = getMachineFunction();
@@ -94,26 +110,50 @@ void MipsCCState::PreAnalyzeReturnForF128(
   }
 }
 
-/// Identify lowered values that originated from f128 arguments and record
+/// Identify lower values that originated from vXfXX and record
+/// this.
+void MipsCCState::PreAnalyzeCallResultForVectorFloat(
+    const SmallVectorImpl<ISD::InputArg> &Ins,
+    const TargetLowering::CallLoweringInfo &CLI) {
+  for (unsigned i = 0; i < Ins.size(); ++i) {
+    OriginalRetWasFloatVector.push_back(
+        originalTypeIsVectorFloat(CLI.RetTy));
+  }
+}
+
+/// Identify lowered values that originated from vXfXX arguments and record
 /// this.
+void MipsCCState::PreAnalyzeReturnForVectorFloat(
+    const SmallVectorImpl<ISD::OutputArg> &Outs) {
+  for (unsigned i = 0; i < Outs.size(); ++i) {
+    ISD::OutputArg Out = Outs[i];
+    OriginalRetWasFloatVector.push_back(
+        originalEVTTypeIsVectorFloat(Out.ArgVT));
+  }
+}
+/// Identify lowered values that originated from f128, float and sret to vXfXX
+/// arguments and record this.
 void MipsCCState::PreAnalyzeCallOperands(
     const SmallVectorImpl<ISD::OutputArg> &Outs,
     std::vector<TargetLowering::ArgListEntry> &FuncArgs,
     const SDNode *CallNode) {
   for (unsigned i = 0; i < Outs.size(); ++i) {
-    OriginalArgWasF128.push_back(
-        originalTypeIsF128(FuncArgs[Outs[i].OrigArgIndex].Ty, CallNode));
-    OriginalArgWasFloat.push_back(
-        FuncArgs[Outs[i].OrigArgIndex].Ty->isFloatingPointTy());
+    TargetLowering::ArgListEntry FuncArg = FuncArgs[Outs[i].OrigArgIndex];
+
+    OriginalArgWasF128.push_back(originalTypeIsF128(FuncArg.Ty, CallNode));
+    OriginalArgWasFloat.push_back(FuncArg.Ty->isFloatingPointTy());
+
+    OriginalArgWasFloatVector.push_back(FuncArg.Ty->isVectorTy());
     CallOperandIsFixed.push_back(Outs[i].IsFixed);
   }
 }
 
-/// Identify lowered values that originated from f128 arguments and record
-/// this.
+/// Identify lowered values that originated from f128, float and vXfXX arguments
+/// and record this.
 void MipsCCState::PreAnalyzeFormalArgumentsForF128(
     const SmallVectorImpl<ISD::InputArg> &Ins) {
   const MachineFunction &MF = getMachineFunction();
+
   for (unsigned i = 0; i < Ins.size(); ++i) {
     Function::const_arg_iterator FuncArg = MF.getFunction()->arg_begin();
 
@@ -123,6 +163,7 @@ void MipsCCState::PreAnalyzeFormalArgumentsForF128(
     if (Ins[i].Flags.isSRet()) {
       OriginalArgWasF128.push_back(false);
       OriginalArgWasFloat.push_back(false);
+      OriginalArgWasFloatVector.push_back(false);
       continue;
     }
 
@@ -132,5 +173,10 @@ void MipsCCState::PreAnalyzeFormalArgumentsForF128(
     OriginalArgWasF128.push_back(
         originalTypeIsF128(FuncArg->getType(), nullptr));
     OriginalArgWasFloat.push_back(FuncArg->getType()->isFloatingPointTy());
+
+    // The MIPS vector ABI exhibits a corner case of sorts or quirk; if the
+    // first argument is actually an SRet pointer to a vector, then the next
+    // argument slot is $a2.
+    OriginalArgWasFloatVector.push_back(FuncArg->getType()->isVectorTy());
   }
 }
diff --git a/llvm/lib/Target/Mips/MipsCCState.h b/llvm/lib/Target/Mips/MipsCCState.h
index 081c393a09b..d86bb85126b 100644
--- a/llvm/lib/Target/Mips/MipsCCState.h
+++ b/llvm/lib/Target/Mips/MipsCCState.h
@@ -45,16 +45,33 @@ private:
                          const SDNode *CallNode);
 
   /// Identify lowered values that originated from f128 arguments and record
-  /// this.
+  /// this for use by RetCC_MipsN.
   void
   PreAnalyzeFormalArgumentsForF128(const SmallVectorImpl<ISD::InputArg> &Ins);
 
+  void PreAnalyzeCallResultForVectorFloat(
+      const SmallVectorImpl<ISD::InputArg> &Ins,
+      const TargetLowering::CallLoweringInfo &CLI);
+
+  void PreAnalyzeFormalArgumentsForVectorFloat(
+      const SmallVectorImpl<ISD::InputArg> &Ins);
+
+  void
+  PreAnalyzeReturnForVectorFloat(const SmallVectorImpl<ISD::OutputArg> &Outs);
+
   /// Records whether the value has been lowered from an f128.
   SmallVector<bool, 4> OriginalArgWasF128;
 
   /// Records whether the value has been lowered from float.
   SmallVector<bool, 4> OriginalArgWasFloat;
 
+  /// Records whether the value has been lowered from a floating point vector.
+  SmallVector<bool, 4> OriginalArgWasFloatVector;
+
+  /// Records whether the return value has been lowered from a floating point
+  /// vector.
+  SmallVector<bool, 4> OriginalRetWasFloatVector;
+
   /// Records whether the value was a fixed argument.
   /// See ISD::OutputArg::IsFixed,
   SmallVector<bool, 4> CallOperandIsFixed;
@@ -78,6 +95,7 @@ public:
     CCState::AnalyzeCallOperands(Outs, Fn);
     OriginalArgWasF128.clear();
     OriginalArgWasFloat.clear();
+    OriginalArgWasFloatVector.clear();
     CallOperandIsFixed.clear();
   }
 
@@ -96,31 +114,38 @@ public:
     CCState::AnalyzeFormalArguments(Ins, Fn);
     OriginalArgWasFloat.clear();
     OriginalArgWasF128.clear();
+    OriginalArgWasFloatVector.clear();
   }
 
   void AnalyzeCallResult(const SmallVectorImpl<ISD::InputArg> &Ins,
                          CCAssignFn Fn,
                          const TargetLowering::CallLoweringInfo &CLI) {
     PreAnalyzeCallResultForF128(Ins, CLI);
+    PreAnalyzeCallResultForVectorFloat(Ins, CLI);
     CCState::AnalyzeCallResult(Ins, Fn);
     OriginalArgWasFloat.clear();
     OriginalArgWasF128.clear();
+    OriginalArgWasFloatVector.clear();
   }
 
   void AnalyzeReturn(const SmallVectorImpl<ISD::OutputArg> &Outs,
                      CCAssignFn Fn) {
     PreAnalyzeReturnForF128(Outs);
+    PreAnalyzeReturnForVectorFloat(Outs);
     CCState::AnalyzeReturn(Outs, Fn);
     OriginalArgWasFloat.clear();
     OriginalArgWasF128.clear();
+    OriginalArgWasFloatVector.clear();
   }
 
   bool CheckReturn(const SmallVectorImpl<ISD::OutputArg> &ArgsFlags,
                    CCAssignFn Fn) {
     PreAnalyzeReturnForF128(ArgsFlags);
+    PreAnalyzeReturnForVectorFloat(ArgsFlags);
     bool Return = CCState::CheckReturn(ArgsFlags, Fn);
     OriginalArgWasFloat.clear();
     OriginalArgWasF128.clear();
+    OriginalArgWasFloatVector.clear();
     return Return;
   }
 
@@ -128,6 +153,13 @@ public:
   bool WasOriginalArgFloat(unsigned ValNo) {
       return OriginalArgWasFloat[ValNo];
   }
+  bool WasOriginalArgVectorFloat(unsigned ValNo) const {
+    return OriginalArgWasFloatVector[ValNo];
+  }
+  bool WasOriginalRetVectorFloat(unsigned ValNo) const {
+    return OriginalRetWasFloatVector[ValNo];
+  }
+
   bool IsCallOperandFixed(unsigned ValNo) { return CallOperandIsFixed[ValNo]; }
   SpecialCallingConvType getSpecialCallingConv() { return SpecialCallingConv; }
 };
diff --git a/llvm/lib/Target/Mips/MipsCallingConv.td b/llvm/lib/Target/Mips/MipsCallingConv.td
index a57cb7badc1..b5df78f89a6 100644
--- a/llvm/lib/Target/Mips/MipsCallingConv.td
+++ b/llvm/lib/Target/Mips/MipsCallingConv.td
@@ -37,6 +37,10 @@ class CCIfOrigArgWasF128<CCAction A>
 class CCIfArgIsVarArg<CCAction A>
     : CCIf<"!static_cast<MipsCCState *>(&State)->IsCallOperandFixed(ValNo)", A>;
 
+/// Match if the return was a floating point vector.
+class CCIfOrigArgWasNotVectorFloat<CCAction A>
+    : CCIf<"!static_cast<MipsCCState *>(&State)"
+                "->WasOriginalRetVectorFloat(ValNo)", A>;
 
 /// Match if the special calling conv is the specified value.
 class CCIfSpecialCallingConv<string CC, CCAction A>
@@ -93,8 +97,10 @@ def RetCC_MipsO32 : CallingConv<[
   // Promote i1/i8/i16 return values to i32.
   CCIfType<[i1, i8, i16], CCPromoteToType<i32>>,
 
-  // i32 are returned in registers V0, V1, A0, A1
-  CCIfType<[i32], CCAssignToReg<[V0, V1, A0, A1]>>,
+  // i32 are returned in registers V0, V1, A0, A1, unless the original return
+  // type was a vector of floats.
+  CCIfOrigArgWasNotVectorFloat<CCIfType<[i32],
+                                        CCAssignToReg<[V0, V1, A0, A1]>>>,
 
   // f32 are returned in registers F0, F2
   CCIfType<[f32], CCAssignToReg<[F0, F2]>>,
diff --git a/llvm/lib/Target/Mips/MipsISelLowering.cpp b/llvm/lib/Target/Mips/MipsISelLowering.cpp
index 93c5f496ce9..a726e25f0b0 100644
--- a/llvm/lib/Target/Mips/MipsISelLowering.cpp
+++ b/llvm/lib/Target/Mips/MipsISelLowering.cpp
@@ -71,6 +71,48 @@ static bool isShiftedMask(uint64_t I, uint64_t &Pos, uint64_t &Size) {
   return true;
 }
 
+// The MIPS MSA ABI passes vector arguments in the integer register set.
+// The number of integer registers used is dependant on the ABI used.
+MVT MipsTargetLowering::getRegisterTypeForCallingConv(MVT VT) const {
+  if (VT.isVector() && Subtarget.hasMSA())
+    return Subtarget.isABI_O32() ? MVT::i32 : MVT::i64;
+  return MipsTargetLowering::getRegisterType(VT);
+}
+
+MVT MipsTargetLowering::getRegisterTypeForCallingConv(LLVMContext &Context,
+                                                      EVT VT) const {
+  if (VT.isVector()) {
+      if (Subtarget.isABI_O32()) {
+        return MVT::i32;
+      } else {
+        return (VT.getSizeInBits() == 32) ? MVT::i32 : MVT::i64;
+      }
+  }
+  return MipsTargetLowering::getRegisterType(Context, VT);
+}
+
+unsigned MipsTargetLowering::getNumRegistersForCallingConv(LLVMContext &Context,
+                                                           EVT VT) const {
+  if (VT.isVector())
+    return std::max((VT.getSizeInBits() / (Subtarget.isABI_O32() ? 32 : 64)),
+                    1U);
+  return MipsTargetLowering::getNumRegisters(Context, VT);
+}
+
+unsigned MipsTargetLowering::getVectorTypeBreakdownForCallingConv(
+    LLVMContext &Context, EVT VT, EVT &IntermediateVT,
+    unsigned &NumIntermediates, MVT &RegisterVT) const {
+
+  // Break down vector types to either 2 i64s or 4 i32s.
+  RegisterVT = getRegisterTypeForCallingConv(Context, VT) ;
+  IntermediateVT = RegisterVT;
+  NumIntermediates = VT.getSizeInBits() < RegisterVT.getSizeInBits()
+                         ? VT.getVectorNumElements()
+                         : VT.getSizeInBits() / RegisterVT.getSizeInBits();
+
+  return NumIntermediates;
+}
+
 SDValue MipsTargetLowering::getGlobalReg(SelectionDAG &DAG, EVT Ty) const {
   MipsFunctionInfo *FI = DAG.getMachineFunction().getInfo<MipsFunctionInfo>();
   return DAG.getRegister(FI->getGlobalBaseReg(), Ty);
@@ -2515,6 +2557,11 @@ SDValue MipsTargetLowering::lowerFP_TO_SINT(SDValue Op,
 //       yet to hold an argument. Otherwise, use A2, A3 and stack. If A1 is
 //       not used, it must be shadowed. If only A3 is available, shadow it and
 //       go to stack.
+// vXiX - Received as scalarized i32s, passed in A0 - A3 and the stack.
+// vXf32 - Passed in either a pair of registers {A0, A1}, {A2, A3} or {A0 - A3}
+//         with the remainder spilled to the stack.
+// vXf64 - Passed in either {A0, A1, A2, A3} or {A2, A3} and in both cases
+//         spilling the remainder to the stack.
 //
 //  For vararg functions, all arguments are passed in A0, A1, A2, A3 and stack.
 //===----------------------------------------------------------------------===//
@@ -2526,8 +2573,13 @@ static bool CC_MipsO32(unsigned ValNo, MVT ValVT, MVT LocVT,
       State.getMachineFunction().getSubtarget());
 
   static const MCPhysReg IntRegs[] = { Mips::A0, Mips::A1, Mips::A2, Mips::A3 };
+
+  const MipsCCState * MipsState = static_cast<MipsCCState *>(&State);
+
   static const MCPhysReg F32Regs[] = { Mips::F12, Mips::F14 };
 
+  static const MCPhysReg FloatVectorIntRegs[] = { Mips::A0, Mips::A2 };
+
   // Do not process byval args here.
   if (ArgFlags.isByVal())
     return true;
@@ -2565,8 +2617,26 @@ static bool CC_MipsO32(unsigned ValNo, MVT ValVT, MVT LocVT,
                                 State.getFirstUnallocated(F32Regs) != ValNo;
   unsigned OrigAlign = ArgFlags.getOrigAlign();
   bool isI64 = (ValVT == MVT::i32 && OrigAlign == 8);
-
-  if (ValVT == MVT::i32 || (ValVT == MVT::f32 && AllocateFloatsInIntReg)) {
+  bool isVectorFloat = MipsState->WasOriginalArgVectorFloat(ValNo);
+
+  // The MIPS vector ABI for floats passes them in a pair of registers
+  if (ValVT == MVT::i32 && isVectorFloat) {
+    // This is the start of an vector that was scalarized into an unknown number
+    // of components. It doesn't matter how many there are. Allocate one of the
+    // notional 8 byte aligned registers which map onto the argument stack, and
+    // shadow the register lost to alignment requirements.
+    if (ArgFlags.isSplit()) {
+      Reg = State.AllocateReg(FloatVectorIntRegs);
+      if (Reg == Mips::A2)
+        State.AllocateReg(Mips::A1);
+      else if (Reg == 0)
+        State.AllocateReg(Mips::A3);
+    } else {
+      // If we're an intermediate component of the split, we can just attempt to
+      // allocate a register directly.
+      Reg = State.AllocateReg(IntRegs);
+    }
+  } else if (ValVT == MVT::i32 || (ValVT == MVT::f32 && AllocateFloatsInIntReg)) {
     Reg = State.AllocateReg(IntRegs);
     // If this is the first part of an i64 arg,
     // the allocated register must be either A0 or A2.
diff --git a/llvm/lib/Target/Mips/MipsISelLowering.h b/llvm/lib/Target/Mips/MipsISelLowering.h
index 2dcafd51061..0e47ed38f42 100644
--- a/llvm/lib/Target/Mips/MipsISelLowering.h
+++ b/llvm/lib/Target/Mips/MipsISelLowering.h
@@ -248,6 +248,33 @@ namespace llvm {
     bool isCheapToSpeculateCttz() const override;
     bool isCheapToSpeculateCtlz() const override;
 
+    /// Return the register type for a given MVT, ensuring vectors are treated
+    /// as a series of gpr sized integers.
+    virtual MVT getRegisterTypeForCallingConv(MVT VT) const override;
+
+    /// Return the register type for a given MVT, ensuring vectors are treated
+    /// as a series of gpr sized integers.
+    virtual MVT getRegisterTypeForCallingConv(LLVMContext &Context,
+                                              EVT VT) const override;
+
+    /// Return the number of registers for a given MVT, ensuring vectors are
+    /// treated as a series of gpr sized integers.
+    virtual unsigned getNumRegistersForCallingConv(LLVMContext &Context,
+                                                   EVT VT) const override;
+
+    /// Break down vectors to the correct number of gpr sized integers.
+    virtual unsigned getVectorTypeBreakdownForCallingConv(
+        LLVMContext &Context, EVT VT, EVT &IntermediateVT,
+        unsigned &NumIntermediates, MVT &RegisterVT) const override;
+
+    /// Return the correct alignment for the current calling convention.
+    virtual unsigned
+    getABIAlignmentForCallingConv(Type *ArgTy, DataLayout DL) const override {
+      if (ArgTy->isVectorTy())
+        return std::min(DL.getABITypeAlignment(ArgTy), 8U);
+      return DL.getABITypeAlignment(ArgTy);
+    }
+
     ISD::NodeType getExtendForAtomicOps() const override {
       return ISD::SIGN_EXTEND;
     }
diff --git a/llvm/lib/Target/Mips/MipsRegisterInfo.cpp b/llvm/lib/Target/Mips/MipsRegisterInfo.cpp
index 65be350f259..625c80b9d68 100644
--- a/llvm/lib/Target/Mips/MipsRegisterInfo.cpp
+++ b/llvm/lib/Target/Mips/MipsRegisterInfo.cpp
@@ -283,10 +283,12 @@ eliminateFrameIndex(MachineBasicBlock::iterator II, int SPAdj,
   int FrameIndex = MI.getOperand(FIOperandNum).getIndex();
   uint64_t stackSize = MF.getFrameInfo().getStackSize();
   int64_t spOffset = MF.getFrameInfo().getObjectOffset(FrameIndex);
+  unsigned alignment = MF.getFrameInfo().getObjectAlignment(FrameIndex);
 
   DEBUG(errs() << "FrameIndex : " << FrameIndex << "\n"
                << "spOffset   : " << spOffset << "\n"
-               << "stackSize  : " << stackSize << "\n");
+               << "stackSize  : " << stackSize << "\n"
+               << "alignment  : " << alignment << "\n");
 
   eliminateFI(MI, FIOperandNum, FrameIndex, stackSize, spOffset);
 }