[AArch64] Implement support for windows style vararg functions

Pass parameters properly in calls to such functions (pass all
floats in integer registers), and handle va_start properly (allocate
stack immediately below the arguments on the stack, to save the
register arguments into a single continuous array).

Differential Revision: https://reviews.llvm.org/D35006

llvm-svn: 307928

5 files changed, 57 insertions, 8 deletions

diff --git a/llvm/lib/Target/AArch64/AArch64CallingConvention.td b/llvm/lib/Target/AArch64/AArch64CallingConvention.td
index 938779d2369..291bc5ea858 100644
--- a/llvm/lib/Target/AArch64/AArch64CallingConvention.td
+++ b/llvm/lib/Target/AArch64/AArch64CallingConvention.td
@@ -118,6 +118,13 @@ def RetCC_AArch64_AAPCS : CallingConv<[
       CCAssignToReg<[Q0, Q1, Q2, Q3, Q4, Q5, Q6, Q7]>>
 ]>;
 
+// Vararg functions on windows pass floats in integer registers
+def CC_AArch64_Win64_VarArg : CallingConv<[
+  CCIfType<[f16, f32],    CCPromoteToType<f64>>,
+  CCIfType<[f64], CCBitConvertToType<i64>>,
+  CCDelegateTo<CC_AArch64_AAPCS>
+]>;
+
 
 // Darwin uses a calling convention which differs in only two ways
 // from the standard one at this level:
diff --git a/llvm/lib/Target/AArch64/AArch64FastISel.cpp b/llvm/lib/Target/AArch64/AArch64FastISel.cpp
index 3682b62d2b8..97396057dce 100644
--- a/llvm/lib/Target/AArch64/AArch64FastISel.cpp
+++ b/llvm/lib/Target/AArch64/AArch64FastISel.cpp
@@ -5138,6 +5138,7 @@ bool AArch64FastISel::fastSelectInstruction(const Instruction *I) {
   return selectOperator(I, I->getOpcode());
   // Silence warnings.
   (void)&CC_AArch64_DarwinPCS_VarArg;
+  (void)&CC_AArch64_Win64_VarArg;
 }
 
 namespace llvm {
diff --git a/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp b/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
index e96ee7d29b3..2436c4eb76f 100644
--- a/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
@@ -41,6 +41,10 @@
 // |                                   |
 // |-----------------------------------|
 // |                                   |
+// | (Win64 only) varargs from reg     |
+// |                                   |
+// |-----------------------------------|
+// |                                   |
 // | prev_fp, prev_lr                  |
 // | (a.k.a. "frame record")           |
 // |-----------------------------------| <- fp(=x29)
@@ -950,7 +954,12 @@ static void computeCalleeSaveRegisterPairs(
           CC == CallingConv::PreserveMost ||
           (Count & 1) == 0) &&
          "Odd number of callee-saved regs to spill!");
-  unsigned Offset = AFI->getCalleeSavedStackSize();
+  int Offset = AFI->getCalleeSavedStackSize();
+
+  unsigned GPRSaveSize = AFI->getVarArgsGPRSize();
+  const AArch64Subtarget &Subtarget = MF.getSubtarget<AArch64Subtarget>();
+  if (Subtarget.isTargetWindows())
+    Offset -= alignTo(GPRSaveSize, 16);
 
   for (unsigned i = 0; i < Count; ++i) {
     RegPairInfo RPI;
diff --git a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
index bce87c0744b..640c4b0df90 100644
--- a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -2650,6 +2650,8 @@ CCAssignFn *AArch64TargetLowering::CCAssignFnForCall(CallingConv::ID CC,
   case CallingConv::PreserveMost:
   case CallingConv::CXX_FAST_TLS:
   case CallingConv::Swift:
+    if (Subtarget->isTargetWindows() && IsVarArg)
+      return CC_AArch64_Win64_VarArg;
     if (!Subtarget->isTargetDarwin())
       return CC_AArch64_AAPCS;
     return IsVarArg ? CC_AArch64_DarwinPCS_VarArg : CC_AArch64_DarwinPCS;
@@ -2828,6 +2830,8 @@ SDValue AArch64TargetLowering::LowerFormalArguments(
       // The AAPCS variadic function ABI is identical to the non-variadic
       // one. As a result there may be more arguments in registers and we should
       // save them for future reference.
+      // Win64 variadic functions also pass arguments in registers, but all float
+      // arguments are passed in integer registers.
       saveVarArgRegisters(CCInfo, DAG, DL, Chain);
     }
 
@@ -2881,7 +2885,10 @@ void AArch64TargetLowering::saveVarArgRegisters(CCState &CCInfo,
   unsigned GPRSaveSize = 8 * (NumGPRArgRegs - FirstVariadicGPR);
   int GPRIdx = 0;
   if (GPRSaveSize != 0) {
-    GPRIdx = MFI.CreateStackObject(GPRSaveSize, 8, false);
+    if (Subtarget->isTargetWindows())
+      GPRIdx = MFI.CreateFixedObject(GPRSaveSize, -(int)GPRSaveSize, false);
+    else
+      GPRIdx = MFI.CreateStackObject(GPRSaveSize, 8, false);
 
     SDValue FIN = DAG.getFrameIndex(GPRIdx, PtrVT);
 
@@ -2890,7 +2897,11 @@ void AArch64TargetLowering::saveVarArgRegisters(CCState &CCInfo,
       SDValue Val = DAG.getCopyFromReg(Chain, DL, VReg, MVT::i64);
       SDValue Store = DAG.getStore(
           Val.getValue(1), DL, Val, FIN,
-          MachinePointerInfo::getStack(DAG.getMachineFunction(), i * 8));
+          Subtarget->isTargetWindows()
+              ? MachinePointerInfo::getFixedStack(DAG.getMachineFunction(),
+                                                  GPRIdx,
+                                                  (i - FirstVariadicGPR) * 8)
+              : MachinePointerInfo::getStack(DAG.getMachineFunction(), i * 8));
       MemOps.push_back(Store);
       FIN =
           DAG.getNode(ISD::ADD, DL, PtrVT, FIN, DAG.getConstant(8, DL, PtrVT));
@@ -2899,7 +2910,7 @@ void AArch64TargetLowering::saveVarArgRegisters(CCState &CCInfo,
   FuncInfo->setVarArgsGPRIndex(GPRIdx);
   FuncInfo->setVarArgsGPRSize(GPRSaveSize);
 
-  if (Subtarget->hasFPARMv8()) {
+  if (Subtarget->hasFPARMv8() && !Subtarget->isTargetWindows()) {
     static const MCPhysReg FPRArgRegs[] = {
         AArch64::Q0, AArch64::Q1, AArch64::Q2, AArch64::Q3,
         AArch64::Q4, AArch64::Q5, AArch64::Q6, AArch64::Q7};
@@ -4491,6 +4502,21 @@ SDValue AArch64TargetLowering::LowerDarwin_VASTART(SDValue Op,
                       MachinePointerInfo(SV));
 }
 
+SDValue AArch64TargetLowering::LowerWin64_VASTART(SDValue Op,
+                                                  SelectionDAG &DAG) const {
+  AArch64FunctionInfo *FuncInfo =
+      DAG.getMachineFunction().getInfo<AArch64FunctionInfo>();
+
+  SDLoc DL(Op);
+  SDValue FR = DAG.getFrameIndex(FuncInfo->getVarArgsGPRSize() > 0
+                                     ? FuncInfo->getVarArgsGPRIndex()
+                                     : FuncInfo->getVarArgsStackIndex(),
+                                 getPointerTy(DAG.getDataLayout()));
+  const Value *SV = cast<SrcValueSDNode>(Op.getOperand(2))->getValue();
+  return DAG.getStore(Op.getOperand(0), DL, FR, Op.getOperand(1),
+                      MachinePointerInfo(SV));
+}
+
 SDValue AArch64TargetLowering::LowerAAPCS_VASTART(SDValue Op,
                                                 SelectionDAG &DAG) const {
   // The layout of the va_list struct is specified in the AArch64 Procedure Call
@@ -4562,8 +4588,12 @@ SDValue AArch64TargetLowering::LowerAAPCS_VASTART(SDValue Op,
 
 SDValue AArch64TargetLowering::LowerVASTART(SDValue Op,
                                             SelectionDAG &DAG) const {
-  return Subtarget->isTargetDarwin() ? LowerDarwin_VASTART(Op, DAG)
-                                     : LowerAAPCS_VASTART(Op, DAG);
+  if (Subtarget->isTargetWindows())
+    return LowerWin64_VASTART(Op, DAG);
+  else if (Subtarget->isTargetDarwin())
+    return LowerDarwin_VASTART(Op, DAG);
+  else
+    return LowerAAPCS_VASTART(Op, DAG);
 }
 
 SDValue AArch64TargetLowering::LowerVACOPY(SDValue Op,
@@ -4571,7 +4601,8 @@ SDValue AArch64TargetLowering::LowerVACOPY(SDValue Op,
   // AAPCS has three pointers and two ints (= 32 bytes), Darwin has single
   // pointer.
   SDLoc DL(Op);
-  unsigned VaListSize = Subtarget->isTargetDarwin() ? 8 : 32;
+  unsigned VaListSize =
+      Subtarget->isTargetDarwin() || Subtarget->isTargetWindows() ? 8 : 32;
   const Value *DestSV = cast<SrcValueSDNode>(Op.getOperand(3))->getValue();
   const Value *SrcSV = cast<SrcValueSDNode>(Op.getOperand(4))->getValue();
 
@@ -10780,7 +10811,7 @@ bool AArch64TargetLowering::isIntDivCheap(EVT VT, AttributeList Attr) const {
 
 unsigned
 AArch64TargetLowering::getVaListSizeInBits(const DataLayout &DL) const {
-  if (Subtarget->isTargetDarwin())
+  if (Subtarget->isTargetDarwin() || Subtarget->isTargetWindows())
     return getPointerTy(DL).getSizeInBits();
 
   return 3 * getPointerTy(DL).getSizeInBits() + 2 * 32;
diff --git a/llvm/lib/Target/AArch64/AArch64ISelLowering.h b/llvm/lib/Target/AArch64/AArch64ISelLowering.h
index ecc2517fb28..69a1ac2a5e9 100644
--- a/llvm/lib/Target/AArch64/AArch64ISelLowering.h
+++ b/llvm/lib/Target/AArch64/AArch64ISelLowering.h
@@ -541,6 +541,7 @@ private:
   SDValue LowerBlockAddress(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerAAPCS_VASTART(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerDarwin_VASTART(SDValue Op, SelectionDAG &DAG) const;
+  SDValue LowerWin64_VASTART(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerVASTART(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerVACOPY(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerVAARG(SDValue Op, SelectionDAG &DAG) const;