1//===- AVR.cpp ------------------------------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#include "ABIInfoImpl.h"
10#include "TargetInfo.h"
11#include "clang/Basic/DiagnosticFrontend.h"
12
13using namespace clang;
14using namespace clang::CodeGen;
15
16//===----------------------------------------------------------------------===//
17// AVR ABI Implementation. Documented at
18// https://gcc.gnu.org/wiki/avr-gcc#Calling_Convention
19// https://gcc.gnu.org/wiki/avr-gcc#Reduced_Tiny
20//===----------------------------------------------------------------------===//
21
22namespace {
23class AVRABIInfo : public DefaultABIInfo {
24private:
25  // The total amount of registers can be used to pass parameters. It is 18 on
26  // AVR, or 6 on AVRTiny.
27  const unsigned ParamRegs;
28  // The total amount of registers can be used to pass return value. It is 8 on
29  // AVR, or 4 on AVRTiny.
30  const unsigned RetRegs;
31
32public:
33  AVRABIInfo(CodeGenTypes &CGT, unsigned NPR, unsigned NRR)
34      : DefaultABIInfo(CGT), ParamRegs(NPR), RetRegs(NRR) {}
35
36  ABIArgInfo classifyReturnType(QualType Ty, bool &LargeRet) const {
37    // On AVR, a return struct with size less than or equals to 8 bytes is
38    // returned directly via registers R18-R25. On AVRTiny, a return struct
39    // with size less than or equals to 4 bytes is returned directly via
40    // registers R22-R25.
41    if (isAggregateTypeForABI(Ty) &&
42        getContext().getTypeSize(Ty) <= RetRegs * 8)
43      return ABIArgInfo::getDirect();
44    // A return value (struct or scalar) with larger size is returned via a
45    // stack slot, along with a pointer as the function's implicit argument.
46    if (getContext().getTypeSize(Ty) > RetRegs * 8) {
47      LargeRet = true;
48      return getNaturalAlignIndirect(Ty);
49    }
50    // An i8 return value should not be extended to i16, since AVR has 8-bit
51    // registers.
52    if (Ty->isIntegralOrEnumerationType() && getContext().getTypeSize(Ty) <= 8)
53      return ABIArgInfo::getDirect();
54    // Otherwise we follow the default way which is compatible.
55    return DefaultABIInfo::classifyReturnType(Ty);
56  }
57
58  ABIArgInfo classifyArgumentType(QualType Ty, unsigned &NumRegs) const {
59    unsigned TySize = getContext().getTypeSize(Ty);
60
61    // An int8 type argument always costs two registers like an int16.
62    if (TySize == 8 && NumRegs >= 2) {
63      NumRegs -= 2;
64      return ABIArgInfo::getExtend(Ty);
65    }
66
67    // If the argument size is an odd number of bytes, round up the size
68    // to the next even number.
69    TySize = llvm::alignTo(TySize, 16);
70
71    // Any type including an array/struct type can be passed in rgisters,
72    // if there are enough registers left.
73    if (TySize <= NumRegs * 8) {
74      NumRegs -= TySize / 8;
75      return ABIArgInfo::getDirect();
76    }
77
78    // An argument is passed either completely in registers or completely in
79    // memory. Since there are not enough registers left, current argument
80    // and all other unprocessed arguments should be passed in memory.
81    // However we still need to return `ABIArgInfo::getDirect()` other than
82    // `ABIInfo::getNaturalAlignIndirect(Ty)`, otherwise an extra stack slot
83    // will be allocated, so the stack frame layout will be incompatible with
84    // avr-gcc.
85    NumRegs = 0;
86    return ABIArgInfo::getDirect();
87  }
88
89  void computeInfo(CGFunctionInfo &FI) const override {
90    // Decide the return type.
91    bool LargeRet = false;
92    if (!getCXXABI().classifyReturnType(FI))
93      FI.getReturnInfo() = classifyReturnType(FI.getReturnType(), LargeRet);
94
95    // Decide each argument type. The total number of registers can be used for
96    // arguments depends on several factors:
97    // 1. Arguments of varargs functions are passed on the stack. This applies
98    //    even to the named arguments. So no register can be used.
99    // 2. Total 18 registers can be used on avr and 6 ones on avrtiny.
100    // 3. If the return type is a struct with too large size, two registers
101    //    (out of 18/6) will be cost as an implicit pointer argument.
102    unsigned NumRegs = ParamRegs;
103    if (FI.isVariadic())
104      NumRegs = 0;
105    else if (LargeRet)
106      NumRegs -= 2;
107    for (auto &I : FI.arguments())
108      I.info = classifyArgumentType(I.type, NumRegs);
109  }
110};
111
112class AVRTargetCodeGenInfo : public TargetCodeGenInfo {
113public:
114  AVRTargetCodeGenInfo(CodeGenTypes &CGT, unsigned NPR, unsigned NRR)
115      : TargetCodeGenInfo(std::make_unique<AVRABIInfo>(CGT, NPR, NRR)) {}
116
117  LangAS getGlobalVarAddressSpace(CodeGenModule &CGM,
118                                  const VarDecl *D) const override {
119    // Check if global/static variable is defined in address space
120    // 1~6 (__flash, __flash1, __flash2, __flash3, __flash4, __flash5)
121    // but not constant.
122    if (D) {
123      LangAS AS = D->getType().getAddressSpace();
124      if (isTargetAddressSpace(AS) && 1 <= toTargetAddressSpace(AS) &&
125          toTargetAddressSpace(AS) <= 6 && !D->getType().isConstQualified())
126        CGM.getDiags().Report(D->getLocation(),
127                              diag::err_verify_nonconst_addrspace)
128            << "__flash*";
129    }
130    return TargetCodeGenInfo::getGlobalVarAddressSpace(CGM, D);
131  }
132
133  void setTargetAttributes(const Decl *D, llvm::GlobalValue *GV,
134                           CodeGen::CodeGenModule &CGM) const override {
135    if (GV->isDeclaration())
136      return;
137    const auto *FD = dyn_cast_or_null<FunctionDecl>(D);
138    if (!FD) return;
139    auto *Fn = cast<llvm::Function>(GV);
140
141    if (FD->getAttr<AVRInterruptAttr>())
142      Fn->addFnAttr("interrupt");
143
144    if (FD->getAttr<AVRSignalAttr>())
145      Fn->addFnAttr("signal");
146  }
147};
148}
149
150std::unique_ptr<TargetCodeGenInfo>
151CodeGen::createAVRTargetCodeGenInfo(CodeGenModule &CGM, unsigned NPR,
152                                    unsigned NRR) {
153  return std::make_unique<AVRTargetCodeGenInfo>(CGM.getTypes(), NPR, NRR);
154}
155