[Clang][LoongArch] Implement ABI lowering

Reuse most of RISCV's implementation with several exceptions:

1. Assign signext/zeroext attribute to args passed in stack.
On RISCV, integer scalars passed in registers have signext/zeroext
when promoted, but are anyext if passed on the stack. This is defined
in early RISCV ABI specification. But after this change [1], integers
should also be signext/zeroext if passed on the stack. So I think
RISCV's ABI lowering should be updated [2].

While in LoongArch ABI spec, we can see that integer scalars narrower
than GRLEN bits are zero/sign-extended no matter passed in registers
or on the stack.

2. Zero-width bit fields are ignored.
This matches GCC's behavior but it hasn't been documented in ABI sepc.
See https://gcc.gnu.org/r12-8294.

3. `char` is signed by default.
There is another difference worth mentioning is that `char` is signed
by default on LoongArch while it is unsigned on RISCV.

This patch also adds `_BitInt` type support to LoongArch and handle it
in LoongArchABIInfo::classifyArgumentType.

[1] https://github.com/riscv-non-isa/riscv-elf-psabi-doc/commit/cec39a064ee0e5b0129973fffab7e3ad1710498f
[2] https://github.com/llvm/llvm-project/issues/57261

Differential Revision: https://reviews.llvm.org/D132285

1 files changed, 443 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/TargetInfo.cpp b/clang/lib/CodeGen/TargetInfo.cpp
index 370614f..2f9adb8 100644
--- a/clang/lib/CodeGen/TargetInfo.cpp
+++ b/clang/lib/CodeGen/TargetInfo.cpp
@@ -11598,6 +11598,438 @@ public:
 
 }
 
+// LoongArch ABI Implementation. Documented at
+// https://loongson.github.io/LoongArch-Documentation/LoongArch-ELF-ABI-EN.html
+//
+//===----------------------------------------------------------------------===//
+
+namespace {
+class LoongArchABIInfo : public DefaultABIInfo {
+private:
+  // Size of the integer ('r') registers in bits.
+  unsigned GRLen;
+  // Size of the floating point ('f') registers in bits.
+  unsigned FRLen;
+  // Number of general-purpose argument registers.
+  static const int NumGARs = 8;
+  // Number of floating-point argument registers.
+  static const int NumFARs = 8;
+  bool detectFARsEligibleStructHelper(QualType Ty, CharUnits CurOff,
+                                      llvm::Type *&Field1Ty,
+                                      CharUnits &Field1Off,
+                                      llvm::Type *&Field2Ty,
+                                      CharUnits &Field2Off) const;
+
+public:
+  LoongArchABIInfo(CodeGen::CodeGenTypes &CGT, unsigned GRLen, unsigned FRLen)
+      : DefaultABIInfo(CGT), GRLen(GRLen), FRLen(FRLen) {}
+
+  void computeInfo(CGFunctionInfo &FI) const override;
+
+  ABIArgInfo classifyArgumentType(QualType Ty, bool IsFixed, int &GARsLeft,
+                                  int &FARsLeft) const;
+  ABIArgInfo classifyReturnType(QualType RetTy) const;
+
+  Address EmitVAArg(CodeGenFunction &CGF, Address VAListAddr,
+                    QualType Ty) const override;
+
+  ABIArgInfo extendType(QualType Ty) const;
+
+  bool detectFARsEligibleStruct(QualType Ty, llvm::Type *&Field1Ty,
+                                CharUnits &Field1Off, llvm::Type *&Field2Ty,
+                                CharUnits &Field2Off, int &NeededArgGPRs,
+                                int &NeededArgFPRs) const;
+  ABIArgInfo coerceAndExpandFARsEligibleStruct(llvm::Type *Field1Ty,
+                                               CharUnits Field1Off,
+                                               llvm::Type *Field2Ty,
+                                               CharUnits Field2Off) const;
+};
+} // end anonymous namespace
+
+void LoongArchABIInfo::computeInfo(CGFunctionInfo &FI) const {
+  QualType RetTy = FI.getReturnType();
+  if (!getCXXABI().classifyReturnType(FI))
+    FI.getReturnInfo() = classifyReturnType(RetTy);
+
+  // IsRetIndirect is true if classifyArgumentType indicated the value should
+  // be passed indirect, or if the type size is a scalar greater than 2*GRLen
+  // and not a complex type with elements <= FRLen. e.g. fp128 is passed direct
+  // in LLVM IR, relying on the backend lowering code to rewrite the argument
+  // list and pass indirectly on LA32.
+  bool IsRetIndirect = FI.getReturnInfo().getKind() == ABIArgInfo::Indirect;
+  if (!IsRetIndirect && RetTy->isScalarType() &&
+      getContext().getTypeSize(RetTy) > (2 * GRLen)) {
+    if (RetTy->isComplexType() && FRLen) {
+      QualType EltTy = RetTy->castAs<ComplexType>()->getElementType();
+      IsRetIndirect = getContext().getTypeSize(EltTy) > FRLen;
+    } else {
+      // This is a normal scalar > 2*GRLen, such as fp128 on LA32.
+      IsRetIndirect = true;
+    }
+  }
+
+  // We must track the number of GARs and FARs used in order to conform to the
+  // LoongArch ABI. As GAR usage is different for variadic arguments, we must
+  // also track whether we are examining a vararg or not.
+  int GARsLeft = IsRetIndirect ? NumGARs - 1 : NumGARs;
+  int FARsLeft = FRLen ? NumFARs : 0;
+  int NumFixedArgs = FI.getNumRequiredArgs();
+
+  int ArgNum = 0;
+  for (auto &ArgInfo : FI.arguments()) {
+    ArgInfo.info = classifyArgumentType(
+        ArgInfo.type, /*IsFixed=*/ArgNum < NumFixedArgs, GARsLeft, FARsLeft);
+    ArgNum++;
+  }
+}
+
+// Returns true if the struct is a potential candidate to be passed in FARs (and
+// GARs). If this function returns true, the caller is responsible for checking
+// that if there is only a single field then that field is a float.
+bool LoongArchABIInfo::detectFARsEligibleStructHelper(
+    QualType Ty, CharUnits CurOff, llvm::Type *&Field1Ty, CharUnits &Field1Off,
+    llvm::Type *&Field2Ty, CharUnits &Field2Off) const {
+  bool IsInt = Ty->isIntegralOrEnumerationType();
+  bool IsFloat = Ty->isRealFloatingType();
+
+  if (IsInt || IsFloat) {
+    uint64_t Size = getContext().getTypeSize(Ty);
+    if (IsInt && Size > GRLen)
+      return false;
+    // Can't be eligible if larger than the FP registers. Half precision isn't
+    // currently supported on LoongArch and the ABI hasn't been confirmed, so
+    // default to the integer ABI in that case.
+    if (IsFloat && (Size > FRLen || Size < 32))
+      return false;
+    // Can't be eligible if an integer type was already found (int+int pairs
+    // are not eligible).
+    if (IsInt && Field1Ty && Field1Ty->isIntegerTy())
+      return false;
+    if (!Field1Ty) {
+      Field1Ty = CGT.ConvertType(Ty);
+      Field1Off = CurOff;
+      return true;
+    }
+    if (!Field2Ty) {
+      Field2Ty = CGT.ConvertType(Ty);
+      Field2Off = CurOff;
+      return true;
+    }
+    return false;
+  }
+
+  if (auto CTy = Ty->getAs<ComplexType>()) {
+    if (Field1Ty)
+      return false;
+    QualType EltTy = CTy->getElementType();
+    if (getContext().getTypeSize(EltTy) > FRLen)
+      return false;
+    Field1Ty = CGT.ConvertType(EltTy);
+    Field1Off = CurOff;
+    Field2Ty = Field1Ty;
+    Field2Off = Field1Off + getContext().getTypeSizeInChars(EltTy);
+    return true;
+  }
+
+  if (const ConstantArrayType *ATy = getContext().getAsConstantArrayType(Ty)) {
+    uint64_t ArraySize = ATy->getSize().getZExtValue();
+    QualType EltTy = ATy->getElementType();
+    CharUnits EltSize = getContext().getTypeSizeInChars(EltTy);
+    for (uint64_t i = 0; i < ArraySize; ++i) {
+      if (!detectFARsEligibleStructHelper(EltTy, CurOff, Field1Ty, Field1Off,
+                                          Field2Ty, Field2Off))
+        return false;
+      CurOff += EltSize;
+    }
+    return true;
+  }
+
+  if (const auto *RTy = Ty->getAs<RecordType>()) {
+    // Structures with either a non-trivial destructor or a non-trivial
+    // copy constructor are not eligible for the FP calling convention.
+    if (getRecordArgABI(Ty, CGT.getCXXABI()))
+      return false;
+    if (isEmptyRecord(getContext(), Ty, true))
+      return true;
+    const RecordDecl *RD = RTy->getDecl();
+    // Unions aren't eligible unless they're empty (which is caught above).
+    if (RD->isUnion())
+      return false;
+    const ASTRecordLayout &Layout = getContext().getASTRecordLayout(RD);
+    // If this is a C++ record, check the bases first.
+    if (const CXXRecordDecl *CXXRD = dyn_cast<CXXRecordDecl>(RD)) {
+      for (const CXXBaseSpecifier &B : CXXRD->bases()) {
+        const auto *BDecl =
+            cast<CXXRecordDecl>(B.getType()->castAs<RecordType>()->getDecl());
+        if (!detectFARsEligibleStructHelper(
+                B.getType(), CurOff + Layout.getBaseClassOffset(BDecl),
+                Field1Ty, Field1Off, Field2Ty, Field2Off))
+          return false;
+      }
+    }
+    for (const FieldDecl *FD : RD->fields()) {
+      QualType QTy = FD->getType();
+      if (FD->isBitField()) {
+        unsigned BitWidth = FD->getBitWidthValue(getContext());
+        // Zero-width bitfields are ignored.
+        if (BitWidth == 0)
+          continue;
+        // Allow a bitfield with a type greater than GRLen as long as the
+        // bitwidth is GRLen or less.
+        if (getContext().getTypeSize(QTy) > GRLen && BitWidth <= GRLen) {
+          QTy = getContext().getIntTypeForBitwidth(GRLen, false);
+        }
+      }
+
+      if (!detectFARsEligibleStructHelper(
+              QTy,
+              CurOff + getContext().toCharUnitsFromBits(
+                           Layout.getFieldOffset(FD->getFieldIndex())),
+              Field1Ty, Field1Off, Field2Ty, Field2Off))
+        return false;
+    }
+    return Field1Ty != nullptr;
+  }
+
+  return false;
+}
+
+// Determine if a struct is eligible to be passed in FARs (and GARs) (i.e., when
+// flattened it contains a single fp value, fp+fp, or int+fp of appropriate
+// size). If so, NeededFARs and NeededGARs are incremented appropriately.
+bool LoongArchABIInfo::detectFARsEligibleStruct(
+    QualType Ty, llvm::Type *&Field1Ty, CharUnits &Field1Off,
+    llvm::Type *&Field2Ty, CharUnits &Field2Off, int &NeededGARs,
+    int &NeededFARs) const {
+  Field1Ty = nullptr;
+  Field2Ty = nullptr;
+  NeededGARs = 0;
+  NeededFARs = 0;
+  if (!detectFARsEligibleStructHelper(Ty, CharUnits::Zero(), Field1Ty,
+                                      Field1Off, Field2Ty, Field2Off))
+    return false;
+  // Not really a candidate if we have a single int but no float.
+  if (Field1Ty && !Field2Ty && !Field1Ty->isFloatingPointTy())
+    return false;
+  if (Field1Ty && Field1Ty->isFloatingPointTy())
+    NeededFARs++;
+  else if (Field1Ty)
+    NeededGARs++;
+  if (Field2Ty && Field2Ty->isFloatingPointTy())
+    NeededFARs++;
+  else if (Field2Ty)
+    NeededGARs++;
+  return true;
+}
+
+// Call getCoerceAndExpand for the two-element flattened struct described by
+// Field1Ty, Field1Off, Field2Ty, Field2Off. This method will create an
+// appropriate coerceToType and unpaddedCoerceToType.
+ABIArgInfo LoongArchABIInfo::coerceAndExpandFARsEligibleStruct(
+    llvm::Type *Field1Ty, CharUnits Field1Off, llvm::Type *Field2Ty,
+    CharUnits Field2Off) const {
+  SmallVector<llvm::Type *, 3> CoerceElts;
+  SmallVector<llvm::Type *, 2> UnpaddedCoerceElts;
+  if (!Field1Off.isZero())
+    CoerceElts.push_back(llvm::ArrayType::get(
+        llvm::Type::getInt8Ty(getVMContext()), Field1Off.getQuantity()));
+
+  CoerceElts.push_back(Field1Ty);
+  UnpaddedCoerceElts.push_back(Field1Ty);
+
+  if (!Field2Ty) {
+    return ABIArgInfo::getCoerceAndExpand(
+        llvm::StructType::get(getVMContext(), CoerceElts, !Field1Off.isZero()),
+        UnpaddedCoerceElts[0]);
+  }
+
+  CharUnits Field2Align =
+      CharUnits::fromQuantity(getDataLayout().getABITypeAlignment(Field2Ty));
+  CharUnits Field1End =
+      Field1Off +
+      CharUnits::fromQuantity(getDataLayout().getTypeStoreSize(Field1Ty));
+  CharUnits Field2OffNoPadNoPack = Field1End.alignTo(Field2Align);
+
+  CharUnits Padding = CharUnits::Zero();
+  if (Field2Off > Field2OffNoPadNoPack)
+    Padding = Field2Off - Field2OffNoPadNoPack;
+  else if (Field2Off != Field2Align && Field2Off > Field1End)
+    Padding = Field2Off - Field1End;
+
+  bool IsPacked = !Field2Off.isMultipleOf(Field2Align);
+
+  if (!Padding.isZero())
+    CoerceElts.push_back(llvm::ArrayType::get(
+        llvm::Type::getInt8Ty(getVMContext()), Padding.getQuantity()));
+
+  CoerceElts.push_back(Field2Ty);
+  UnpaddedCoerceElts.push_back(Field2Ty);
+
+  return ABIArgInfo::getCoerceAndExpand(
+      llvm::StructType::get(getVMContext(), CoerceElts, IsPacked),
+      llvm::StructType::get(getVMContext(), UnpaddedCoerceElts, IsPacked));
+}
+
+ABIArgInfo LoongArchABIInfo::classifyArgumentType(QualType Ty, bool IsFixed,
+                                                  int &GARsLeft,
+                                                  int &FARsLeft) const {
+  assert(GARsLeft <= NumGARs && "GAR tracking underflow");
+  Ty = useFirstFieldIfTransparentUnion(Ty);
+
+  // Structures with either a non-trivial destructor or a non-trivial
+  // copy constructor are always passed indirectly.
+  if (CGCXXABI::RecordArgABI RAA = getRecordArgABI(Ty, getCXXABI())) {
+    if (GARsLeft)
+      GARsLeft -= 1;
+    return getNaturalAlignIndirect(Ty, /*ByVal=*/RAA ==
+                                           CGCXXABI::RAA_DirectInMemory);
+  }
+
+  // Ignore empty structs/unions.
+  if (isEmptyRecord(getContext(), Ty, true))
+    return ABIArgInfo::getIgnore();
+
+  uint64_t Size = getContext().getTypeSize(Ty);
+
+  // Pass floating point values via FARs if possible.
+  if (IsFixed && Ty->isFloatingType() && !Ty->isComplexType() &&
+      FRLen >= Size && FARsLeft) {
+    FARsLeft--;
+    return ABIArgInfo::getDirect();
+  }
+
+  // Complex types for the *f or *d ABI must be passed directly rather than
+  // using CoerceAndExpand.
+  if (IsFixed && Ty->isComplexType() && FRLen && FARsLeft >= 2) {
+    QualType EltTy = Ty->castAs<ComplexType>()->getElementType();
+    if (getContext().getTypeSize(EltTy) <= FRLen) {
+      FARsLeft -= 2;
+      return ABIArgInfo::getDirect();
+    }
+  }
+
+  if (IsFixed && FRLen && Ty->isStructureOrClassType()) {
+    llvm::Type *Field1Ty = nullptr;
+    llvm::Type *Field2Ty = nullptr;
+    CharUnits Field1Off = CharUnits::Zero();
+    CharUnits Field2Off = CharUnits::Zero();
+    int NeededGARs = 0;
+    int NeededFARs = 0;
+    bool IsCandidate = detectFARsEligibleStruct(
+        Ty, Field1Ty, Field1Off, Field2Ty, Field2Off, NeededGARs, NeededFARs);
+    if (IsCandidate && NeededGARs <= GARsLeft && NeededFARs <= FARsLeft) {
+      GARsLeft -= NeededGARs;
+      FARsLeft -= NeededFARs;
+      return coerceAndExpandFARsEligibleStruct(Field1Ty, Field1Off, Field2Ty,
+                                               Field2Off);
+    }
+  }
+
+  uint64_t NeededAlign = getContext().getTypeAlign(Ty);
+  // Determine the number of GARs needed to pass the current argument
+  // according to the ABI. 2*GRLen-aligned varargs are passed in "aligned"
+  // register pairs, so may consume 3 registers.
+  int NeededGARs = 1;
+  if (!IsFixed && NeededAlign == 2 * GRLen)
+    NeededGARs = 2 + (GARsLeft % 2);
+  else if (Size > GRLen && Size <= 2 * GRLen)
+    NeededGARs = 2;
+
+  if (NeededGARs > GARsLeft)
+    NeededGARs = GARsLeft;
+
+  GARsLeft -= NeededGARs;
+
+  if (!isAggregateTypeForABI(Ty) && !Ty->isVectorType()) {
+    // Treat an enum type as its underlying type.
+    if (const EnumType *EnumTy = Ty->getAs<EnumType>())
+      Ty = EnumTy->getDecl()->getIntegerType();
+
+    // All integral types are promoted to GRLen width.
+    if (Size < GRLen && Ty->isIntegralOrEnumerationType())
+      return extendType(Ty);
+
+    if (const auto *EIT = Ty->getAs<BitIntType>()) {
+      if (EIT->getNumBits() < GRLen)
+        return extendType(Ty);
+      if (EIT->getNumBits() > 128 ||
+          (!getContext().getTargetInfo().hasInt128Type() &&
+           EIT->getNumBits() > 64))
+        return getNaturalAlignIndirect(Ty, /*ByVal=*/false);
+    }
+
+    return ABIArgInfo::getDirect();
+  }
+
+  // Aggregates which are <= 2*GRLen will be passed in registers if possible,
+  // so coerce to integers.
+  if (Size <= 2 * GRLen) {
+    // Use a single GRLen int if possible, 2*GRLen if 2*GRLen alignment is
+    // required, and a 2-element GRLen array if only GRLen alignment is
+    // required.
+    if (Size <= GRLen) {
+      return ABIArgInfo::getDirect(
+          llvm::IntegerType::get(getVMContext(), GRLen));
+    }
+    if (getContext().getTypeAlign(Ty) == 2 * GRLen) {
+      return ABIArgInfo::getDirect(
+          llvm::IntegerType::get(getVMContext(), 2 * GRLen));
+    }
+    return ABIArgInfo::getDirect(
+        llvm::ArrayType::get(llvm::IntegerType::get(getVMContext(), GRLen), 2));
+  }
+  return getNaturalAlignIndirect(Ty, /*ByVal=*/false);
+}
+
+ABIArgInfo LoongArchABIInfo::classifyReturnType(QualType RetTy) const {
+  if (RetTy->isVoidType())
+    return ABIArgInfo::getIgnore();
+  // The rules for return and argument types are the same, so defer to
+  // classifyArgumentType.
+  int GARsLeft = 2;
+  int FARsLeft = FRLen ? 2 : 0;
+  return classifyArgumentType(RetTy, /*IsFixed=*/true, GARsLeft, FARsLeft);
+}
+
+Address LoongArchABIInfo::EmitVAArg(CodeGenFunction &CGF, Address VAListAddr,
+                                    QualType Ty) const {
+  CharUnits SlotSize = CharUnits::fromQuantity(GRLen / 8);
+
+  // Empty records are ignored for parameter passing purposes.
+  if (isEmptyRecord(getContext(), Ty, true)) {
+    Address Addr = Address(CGF.Builder.CreateLoad(VAListAddr),
+                           getVAListElementType(CGF), SlotSize);
+    Addr = CGF.Builder.CreateElementBitCast(Addr, CGF.ConvertTypeForMem(Ty));
+    return Addr;
+  }
+
+  auto TInfo = getContext().getTypeInfoInChars(Ty);
+
+  // Arguments bigger than 2*GRLen bytes are passed indirectly.
+  return emitVoidPtrVAArg(CGF, VAListAddr, Ty,
+                          /*IsIndirect=*/TInfo.Width > 2 * SlotSize, TInfo,
+                          SlotSize,
+                          /*AllowHigherAlign=*/true);
+}
+
+ABIArgInfo LoongArchABIInfo::extendType(QualType Ty) const {
+  int TySize = getContext().getTypeSize(Ty);
+  // LA64 ABI requires unsigned 32 bit integers to be sign extended.
+  if (GRLen == 64 && Ty->isUnsignedIntegerOrEnumerationType() && TySize == 32)
+    return ABIArgInfo::getSignExtend(Ty);
+  return ABIArgInfo::getExtend(Ty);
+}
+
+namespace {
+class LoongArchTargetCodeGenInfo : public TargetCodeGenInfo {
+public:
+  LoongArchTargetCodeGenInfo(CodeGen::CodeGenTypes &CGT, unsigned GRLen,
+                             unsigned FRLen)
+      : TargetCodeGenInfo(
+            std::make_unique<LoongArchABIInfo>(CGT, GRLen, FRLen)) {}
+};
+} // namespace
+
 //===----------------------------------------------------------------------===//
 // Driver code
 //===----------------------------------------------------------------------===//
@@ -11829,6 +12261,17 @@ const TargetCodeGenInfo &CodeGenModule::getTargetCodeGenInfo() {
   case llvm::Triple::bpfeb:
   case llvm::Triple::bpfel:
     return SetCGInfo(new BPFTargetCodeGenInfo(Types));
+  case llvm::Triple::loongarch32:
+  case llvm::Triple::loongarch64: {
+    StringRef ABIStr = getTarget().getABI();
+    unsigned ABIFRLen = 0;
+    if (ABIStr.endswith("f"))
+      ABIFRLen = 32;
+    else if (ABIStr.endswith("d"))
+      ABIFRLen = 64;
+    return SetCGInfo(new LoongArchTargetCodeGenInfo(
+        Types, getTarget().getPointerWidth(0), ABIFRLen));
+  }
   }
 }