[clang][AVR] Implement standard calling convention for AVR and AVRTiny

This patch implements avr-gcc's calling convention: https://gcc.gnu.org/wiki/avr-gcc#Calling_Convention Reviewed By: aykevl Differential Revision: https://reviews.llvm.org/D120720

Author: benshi001

clang/lib/Basic/Targets/AVR.cpp

@@ -24,7 +24,8 @@ namespace targets {
 struct LLVM_LIBRARY_VISIBILITY MCUInfo {
  const char *Name;
  const char *DefineName;
- const int NumFlashBanks; // -1 means the device does not support LPM/ELPM.
+ const int NumFlashBanks; // Set to 0 for the devices do not support LPM/ELPM.
+ bool IsTiny; // Set to true for the devices belong to the avrtiny family.
 };
 
 // NOTE: This list has been synchronized with gcc-avr 5.4.0 and avr-libc 2.0.0.
@@ -282,14 +283,14 @@ static MCUInfo AVRMcus[] = {
  {"atxmega128a1", "__AVR_ATxmega128A1__", 2},
  {"atxmega128a1u", "__AVR_ATxmega128A1U__", 2},
  {"atxmega128a4u", "__AVR_ATxmega128A4U__", 2},
- {"attiny4", "__AVR_ATtiny4__", 0},
- {"attiny5", "__AVR_ATtiny5__", 0},
- {"attiny9", "__AVR_ATtiny9__", 0},
- {"attiny10", "__AVR_ATtiny10__", 0},
- {"attiny20", "__AVR_ATtiny20__", 0},
- {"attiny40", "__AVR_ATtiny40__", 0},
- {"attiny102", "__AVR_ATtiny102__", 0},
- {"attiny104", "__AVR_ATtiny104__", 0},
+ {"attiny4", "__AVR_ATtiny4__", 0, true},
+ {"attiny5", "__AVR_ATtiny5__", 0, true},
+ {"attiny9", "__AVR_ATtiny9__", 0, true},
+ {"attiny10", "__AVR_ATtiny10__", 0, true},
+ {"attiny20", "__AVR_ATtiny20__", 0, true},
+ {"attiny40", "__AVR_ATtiny40__", 0, true},
+ {"attiny102", "__AVR_ATtiny102__", 0, true},
+ {"attiny104", "__AVR_ATtiny104__", 0, true},
  {"attiny202", "__AVR_ATtiny202__", 1},
  {"attiny402", "__AVR_ATtiny402__", 1},
  {"attiny204", "__AVR_ATtiny204__", 1},
@@ -340,6 +341,27 @@ void AVRTargetInfo::fillValidCPUList(SmallVectorImpl<StringRef> &Values) const {
  Values.push_back(Info.Name);
 }
 
+bool AVRTargetInfo::setCPU(const std::string &Name) {
+ // Set the ABI and CPU fields if parameter Name is a family name.
+ if (llvm::is_contained(ValidFamilyNames, Name)) {
+ CPU = Name;
+ ABI = Name == "avrtiny" ? "avrtiny" : "avr";
+ return true;
+ }
+
+ // Set the ABI field if parameter Name is a device name.
+ auto It = llvm::find_if(
+ AVRMcus, [&](const MCUInfo &Info) { return Info.Name == Name; });
+ if (It != std::end(AVRMcus)) {
+ CPU = Name;
+ ABI = It->IsTiny ? "avrtiny" : "avr";
+ return true;
+ }
+
+ // Parameter Name is neither valid family name nor valid device name.
+ return false;
+}
+
 void AVRTargetInfo::getTargetDefines(const LangOptions &Opts,
  MacroBuilder &Builder) const {
  Builder.defineMacro("AVR");

clang/lib/Basic/Targets/AVR.h

@@ -74,8 +74,7 @@ class LLVM_LIBRARY_VISIBILITY AVRTargetInfo : public TargetInfo {
  static const char *const GCCRegNames[] = {
  "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7", "r8", "r9",
  "r10", "r11", "r12", "r13", "r14", "r15", "r16", "r17", "r18", "r19",
- "r20", "r21", "r22", "r23", "r24", "r25", "X", "Y", "Z", "SP"
- };
+ "r20", "r21", "r22", "r23", "r24", "r25", "X", "Y", "Z", "SP"};
  return llvm::makeArrayRef(GCCRegNames);
  }
 
@@ -169,15 +168,12 @@ class LLVM_LIBRARY_VISIBILITY AVRTargetInfo : public TargetInfo {
 
  bool isValidCPUName(StringRef Name) const override;
  void fillValidCPUList(SmallVectorImpl<StringRef> &Values) const override;
- bool setCPU(const std::string &Name) override {
- bool isValid = isValidCPUName(Name);
- if (isValid)
- CPU = Name;
- return isValid;
- }
+ bool setCPU(const std::string &Name) override;
+ StringRef getABI() const override { return ABI; }
 
 protected:
  std::string CPU;
+ StringRef ABI;
 };
 
 } // namespace targets

clang/lib/CodeGen/TargetInfo.cpp

@@ -19,9 +19,9 @@
 #include "CodeGenFunction.h"
 #include "clang/AST/Attr.h"
 #include "clang/AST/RecordLayout.h"
+#include "clang/Basic/Builtins.h"
 #include "clang/Basic/CodeGenOptions.h"
 #include "clang/Basic/DiagnosticFrontend.h"
-#include "clang/Basic/Builtins.h"
 #include "clang/CodeGen/CGFunctionInfo.h"
 #include "clang/CodeGen/SwiftCallingConv.h"
 #include "llvm/ADT/SmallBitVector.h"
@@ -33,6 +33,7 @@
 #include "llvm/IR/IntrinsicsNVPTX.h"
 #include "llvm/IR/IntrinsicsS390.h"
 #include "llvm/IR/Type.h"
+#include "llvm/Support/MathExtras.h"
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm> // std::sort
 
@@ -8278,32 +8279,93 @@ void M68kTargetCodeGenInfo::setTargetAttributes(
 
 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) : DefaultABIInfo(CGT) {}
+ AVRABIInfo(CodeGenTypes &CGT, unsigned NPR, unsigned NRR)
+ : DefaultABIInfo(CGT), ParamRegs(NPR), RetRegs(NRR) {}
+
+ ABIArgInfo classifyReturnType(QualType Ty, bool &LargeRet) const {
+ if (isAggregateTypeForABI(Ty)) {
+ // 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 (getContext().getTypeSize(Ty) <= RetRegs * 8)
+ return ABIArgInfo::getDirect();
+ // A return struct with larger size is returned via a stack
+ // slot, along with a pointer to it as the function's implicit argument.
+ LargeRet = true;
+ return getNaturalAlignIndirect(Ty);
+ }
+ // Otherwise we follow the default way which is compatible.
+ return DefaultABIInfo::classifyReturnType(Ty);
+ }
 
- ABIArgInfo classifyReturnType(QualType Ty) const {
- // A return struct with size less than or equal to 8 bytes is returned
- // directly via registers R18-R25.
- if (isAggregateTypeForABI(Ty) && getContext().getTypeSize(Ty) <= 64)
+ 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();
- else
- return DefaultABIInfo::classifyReturnType(Ty);
+ }
+
+ // 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();
  }
 
- // Just copy the original implementation of DefaultABIInfo::computeInfo(),
- // since DefaultABIInfo::classify{Return,Argument}Type() are not virtual.
  void computeInfo(CGFunctionInfo &FI) const override {
+ // Decide the return type.
+ bool LargeRet = false;
  if (!getCXXABI().classifyReturnType(FI))
- FI.getReturnInfo() = classifyReturnType(FI.getReturnType());
+ 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);
+ I.info = classifyArgumentType(I.type, NumRegs);
  }
 };
 
 class AVRTargetCodeGenInfo : public TargetCodeGenInfo {
 public:
- AVRTargetCodeGenInfo(CodeGenTypes &CGT)
- : TargetCodeGenInfo(std::make_unique<AVRABIInfo>(CGT)) {}
+ AVRTargetCodeGenInfo(CodeGenTypes &CGT, unsigned NPR, unsigned NRR)
+ : TargetCodeGenInfo(std::make_unique<AVRABIInfo>(CGT, NPR, NRR)) {}
 
  LangAS getGlobalVarAddressSpace(CodeGenModule &CGM,
  const VarDecl *D) const override {
@@ -11280,8 +11342,14 @@ const TargetCodeGenInfo &CodeGenModule::getTargetCodeGenInfo() {
  case llvm::Triple::mips64el:
  return SetCGInfo(new MIPSTargetCodeGenInfo(Types, false));
 
- case llvm::Triple::avr:
- return SetCGInfo(new AVRTargetCodeGenInfo(Types));
+ case llvm::Triple::avr: {
+ // For passing parameters, R8~R25 are used on avr, and R18~R25 are used
+ // on avrtiny. For passing return value, R18~R25 are used on avr, and
+ // R22~R25 are used on avrtiny.
+ unsigned NPR = getTarget().getABI() == "avrtiny" ? 6 : 18;
+ unsigned NRR = getTarget().getABI() == "avrtiny" ? 4 : 8;
+ return SetCGInfo(new AVRTargetCodeGenInfo(Types, NPR, NRR));
+ }
 
  case llvm::Triple::aarch64:
  case llvm::Triple::aarch64_32:

clang/test/CodeGen/avr/argument.c

@@ -0,0 +1,116 @@
+// RUN: %clang_cc1 -triple avr -target-cpu atmega328 -emit-llvm %s -o - \
+// RUN: | FileCheck %s --check-prefix AVR
+// RUN: %clang_cc1 -triple avr -target-cpu attiny40 -emit-llvm %s -o - \
+// RUN: | FileCheck %s --check-prefix TINY
+
+// NOTE: All arguments are passed via the stack for functions with variable arguments.
+// AVR: define {{.*}} i8 @foo0(i8 {{.*}}, i8 {{.*}}, ...)
+// TINY: define {{.*}} i8 @foo0(i8 {{.*}}, i8 {{.*}}, ...)
+// AVR-NOT: define {{.*}} i8 @foo0(i8 {{.*}} signext {{.*}}, i8 {{.*}} signext {{.*}}, ...)
+// TINY-NOT: define {{.*}} i8 @foo0(i8 {{.*}} signext {{.*}}, i8 {{.*}} signext {{.*}}, ...)
+char foo0(char a, char b, ...) {
+ return a + b;
+}
+
+// NOTE: All arguments are passed via registers on both avr and avrtiny.
+// AVR: define {{.*}} i8 @foo1(i32 {{.*}}, i8 {{.*}} signext {{.*}})
+// TINY: define {{.*}} i8 @foo1(i32 {{.*}}, i8 {{.*}} signext {{.*}})
+char foo1(long a, char b) {
+ return a + b;
+}
+
+// NOTE: The argument `char c` is passed via registers on avr, while via the stack on avrtiny.
+// The argument `char b` costs 2 registers, so there is no vacant register left for
+// `char c` on avrtiny.
+// AVR: define {{.*}} i8 @foo2(i32 {{.*}}, i8 {{.*}} signext {{.*}}, i8 {{.*}} signext {{.*}})
+// TINY: define {{.*}} i8 @foo2(i32 {{.*}}, i8 {{.*}} signext {{.*}}, i8 {{.*}})
+// TINY-NOT: define {{.*}} i8 @foo2(i32 {{.*}}, i8 {{.*}} signext {{.*}}, i8 {{.*}} signext {{.*}})
+char foo2(long a, char b, char c) {
+ return a + b + c;
+}
+
+// NOTE: On avr, the argument `a` costs 16 registers and `b` costs 2 registers, so
+// `c` has to be passed via the stack.
+// AVR: define {{.*}} i8 @foo3({{.*}}, i8 {{.*}} signext {{.*}}, i8 {{.*}})
+// AVR-NOT: define {{.*}} i8 @foo3({{.*}}, i8 {{.*}} signext {{.*}}, i8 {{.*}} signext {{.*}})
+// TINY: define {{.*}} i8 @foo3({{.*}}, i8 {{.*}}, i8 {{.*}})
+// TINY-NOT: define {{.*}} i8 @foo3({{.*}}, i8 {{.*}} signext {{.*}}, i8 {{.*}} signext {{.*}})
+struct s15 {
+ char arr[15];
+};
+char foo3(struct s15 a, char b, char c) {
+ return a.arr[b] + a.arr[c];
+}
+
+// NOTE: On avr, `a` only costs 16 registers, though there are 2 vacant registers,
+// both `b` and `c` have to be passed via the stack.
+// AVR: define {{.*}} i8 @foo4({{.*}}, i32 {{.*}}, i8 {{.*}})
+// AVR-NOT: define {{.*}} i8 @foo4({{.*}}, i32 {{.*}}, i8 {{.*}} signext {{.*}})
+// TINY: define {{.*}} i8 @foo4({{.*}}, i32 {{.*}}, i8 {{.*}})
+// TINY-NOT: define {{.*}} i8 @foo4({{.*}}, i32 {{.*}}, i8 {{.*}} signext {{.*}})
+char foo4(struct s15 a, long b, char c) {
+ return a.arr[c];
+}
+
+// NOTE: On avrtiny, `a` only costs 4 registers, though there are 2 vacant
+// registers, both `b` and `c` are passed via the stack.
+// AVR: define {{.*}} i8 @foo5(i32 {{.*}}, i32 {{.*}}, i8 {{.*}} signext {{.*}})
+// TINY: define {{.*}} i8 @foo5(i32 {{.*}}, i32 {{.*}}, i8 {{.*}})
+// TINY-NOT: define {{.*}} i8 @foo5(i32 {{.*}}, i32 {{.*}}, i8 {{.*}} signext {{.*}})
+char foo5(long a, long b, char c) {
+ return c + 1;
+}
+
+// NOTE: All arguments are passed via the stack, though all registers are vacant.
+// AVR: define {{.*}} i8 @foo6({{.*}}, i8 {{.*}})
+// AVR-NOT: define {{.*}} i8 @foo6({{.*}}, i8 {{.*}} signext {{.*}})
+// TINY: define {{.*}} i8 @foo6({{.*}}, i8 {{.*}})
+// TINY-NOT: define {{.*}} i8 @foo6({{.*}}, i8 {{.*}} signext {{.*}})
+struct s32 {
+ char arr[32];
+};
+char foo6(struct s32 a, char b) {
+ return a.arr[b];
+}
+
+// NOTE: All arguments are passed via registers on avr. While all arguments are passed
+// via the stack on avrtiny, though all registers are vacant.
+// AVR: define {{.*}} i8 @foo7({{.*}}, i8 {{.*}} signext {{.*}})
+// TINY: define {{.*}} i8 @foo7({{.*}}, i8 {{.*}})
+// TINY-NOT: define {{.*}} i8 @foo7({{.*}}, i8 {{.*}} signext {{.*}})
+char foo7(struct s15 a, char b) {
+ return a.arr[b];
+}
+
+// NOTE: On avr, though `a` only cost 16 registers, `b` has to be passed via the
+// stack, since there is an implicit pointer argument costs 2 registers.
+// AVR: define {{.*}} @foo8({{.*}}, {{.*}}, i8 {{.*}})
+// AVR-NOT: define {{.*}} @foo8({{.*}}, {{.*}}, i8 {{.*}} signext {{.*}})
+// TINY: define {{.*}} @foo8({{.*}}, {{.*}}, i8 {{.*}})
+// TINY-NOT: define {{.*}} @foo8({{.*}}, {{.*}}, i8 {{.*}} signext {{.*}})
+struct s15 foo8(struct s15 a, char b) {
+ a.arr[0] = b;
+ return a;
+}
+
+// NOTE: On avrtiny, `b` has to be passed via the stack, since there is an
+// implicit pointer argument costs 2 registers.
+// AVR: define {{.*}} @foo9({{.*}}, i32 {{.*}}, i8 {{.*}} signext {{.*}})
+// TINY: define {{.*}} @foo9({{.*}}, i32 {{.*}}, i8 {{.*}})
+// TINY-NOT: define {{.*}} @foo9({{.*}}, i32 {{.*}}, i8 {{.*}} signext {{.*}})
+struct s15 foo9(long a, char b) {
+ struct s15 x;
+ x.arr[0] = b;
+ return x;
+}
+
+// NOTE: All arguments are passed via registers, though there is an implicit
+// pointer argument costs 2 registers.
+// AVR: define {{.*}} @fooa({{.*}}, i8 {{.*}} signext {{.*}}, i8 {{.*}} signext {{.*}})
+// TINY: define {{.*}} @fooa({{.*}}, i8 {{.*}} signext {{.*}}, i8 {{.*}} signext {{.*}})
+struct s15 fooa(char a, char b) {
+ struct s15 x;
+ x.arr[0] = a;
+ x.arr[1] = b;
+ return x;
+}