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//===- AVR.cpp ------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "ABIInfoImpl.h"
#include "TargetInfo.h"
#include "clang/Basic/DiagnosticFrontend.h"
using namespace clang;
using namespace clang::CodeGen;
//===----------------------------------------------------------------------===//
// AVR ABI Implementation. Documented at
// https://gcc.gnu.org/wiki/avr-gcc#Calling_Convention
// https://gcc.gnu.org/wiki/avr-gcc#Reduced_Tiny
//===----------------------------------------------------------------------===//
namespace {
class AVRABIInfo : public DefaultABIInfo {
private:
// The total amount of registers can be used to pass parameters. It is 18 on
// AVR, or 6 on AVRTiny.
const unsigned ParamRegs;
// The total amount of registers can be used to pass return value. It is 8 on
// AVR, or 4 on AVRTiny.
const unsigned RetRegs;
public:
AVRABIInfo(CodeGenTypes &CGT, unsigned NPR, unsigned NRR)
: DefaultABIInfo(CGT), ParamRegs(NPR), RetRegs(NRR) {}
ABIArgInfo classifyReturnType(QualType Ty, bool &LargeRet) const {
// On AVR, a return struct with size less than or equals to 8 bytes is
// returned directly via registers R18-R25. On AVRTiny, a return struct
// with size less than or equals to 4 bytes is returned directly via
// registers R22-R25.
if (isAggregateTypeForABI(Ty) &&
getContext().getTypeSize(Ty) <= RetRegs * 8)
return ABIArgInfo::getDirect();
// A return value (struct or scalar) with larger size is returned via a
// stack slot, along with a pointer as the function's implicit argument.
if (getContext().getTypeSize(Ty) > RetRegs * 8) {
LargeRet = true;
return getNaturalAlignIndirect(Ty);
}
// An i8 return value should not be extended to i16, since AVR has 8-bit
// registers.
if (Ty->isIntegralOrEnumerationType() && getContext().getTypeSize(Ty) <= 8)
return ABIArgInfo::getDirect();
// Otherwise we follow the default way which is compatible.
return DefaultABIInfo::classifyReturnType(Ty);
}
ABIArgInfo classifyArgumentType(QualType Ty, unsigned &NumRegs) const {
unsigned TySize = getContext().getTypeSize(Ty);
// An int8 type argument always costs two registers like an int16.
if (TySize == 8 && NumRegs >= 2) {
NumRegs -= 2;
return ABIArgInfo::getExtend(Ty);
}
// If the argument size is an odd number of bytes, round up the size
// to the next even number.
TySize = llvm::alignTo(TySize, 16);
// Any type including an array/struct type can be passed in rgisters,
// if there are enough registers left.
if (TySize <= NumRegs * 8) {
NumRegs -= TySize / 8;
return ABIArgInfo::getDirect();
}
// An argument is passed either completely in registers or completely in
// memory. Since there are not enough registers left, current argument
// and all other unprocessed arguments should be passed in memory.
// However we still need to return `ABIArgInfo::getDirect()` other than
// `ABIInfo::getNaturalAlignIndirect(Ty)`, otherwise an extra stack slot
// will be allocated, so the stack frame layout will be incompatible with
// avr-gcc.
NumRegs = 0;
return ABIArgInfo::getDirect();
}
void computeInfo(CGFunctionInfo &FI) const override {
// Decide the return type.
bool LargeRet = false;
if (!getCXXABI().classifyReturnType(FI))
FI.getReturnInfo() = classifyReturnType(FI.getReturnType(), LargeRet);
// Decide each argument type. The total number of registers can be used for
// arguments depends on several factors:
// 1. Arguments of varargs functions are passed on the stack. This applies
// even to the named arguments. So no register can be used.
// 2. Total 18 registers can be used on avr and 6 ones on avrtiny.
// 3. If the return type is a struct with too large size, two registers
// (out of 18/6) will be cost as an implicit pointer argument.
unsigned NumRegs = ParamRegs;
if (FI.isVariadic())
NumRegs = 0;
else if (LargeRet)
NumRegs -= 2;
for (auto &I : FI.arguments())
I.info = classifyArgumentType(I.type, NumRegs);
}
};
class AVRTargetCodeGenInfo : public TargetCodeGenInfo {
public:
AVRTargetCodeGenInfo(CodeGenTypes &CGT, unsigned NPR, unsigned NRR)
: TargetCodeGenInfo(std::make_unique<AVRABIInfo>(CGT, NPR, NRR)) {}
LangAS getGlobalVarAddressSpace(CodeGenModule &CGM,
const VarDecl *D) const override {
// Check if global/static variable is defined in address space
// 1~6 (__flash, __flash1, __flash2, __flash3, __flash4, __flash5)
// but not constant.
if (D) {
LangAS AS = D->getType().getAddressSpace();
if (isTargetAddressSpace(AS) && 1 <= toTargetAddressSpace(AS) &&
toTargetAddressSpace(AS) <= 6 && !D->getType().isConstQualified())
CGM.getDiags().Report(D->getLocation(),
diag::err_verify_nonconst_addrspace)
<< "__flash*";
}
return TargetCodeGenInfo::getGlobalVarAddressSpace(CGM, D);
}
void setTargetAttributes(const Decl *D, llvm::GlobalValue *GV,
CodeGen::CodeGenModule &CGM) const override {
if (GV->isDeclaration())
return;
const auto *FD = dyn_cast_or_null<FunctionDecl>(D);
if (!FD) return;
auto *Fn = cast<llvm::Function>(GV);
if (FD->getAttr<AVRInterruptAttr>())
Fn->addFnAttr("interrupt");
if (FD->getAttr<AVRSignalAttr>())
Fn->addFnAttr("signal");
}
};
}
std::unique_ptr<TargetCodeGenInfo>
CodeGen::createAVRTargetCodeGenInfo(CodeGenModule &CGM, unsigned NPR,
unsigned NRR) {
return std::make_unique<AVRTargetCodeGenInfo>(CGM.getTypes(), NPR, NRR);
}
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