[X86] Support MCU psABI when marking inregs

[mkuper]

Summary

The MCU psABI has a calling convention that is somewhat, but not quite, like -mregparm 3.
This adds support for this calling convention.

It depends on D13977 which introduces MCU triple support.

[DavidKreitzer]

lib/CodeGen/TargetInfo.cpp

1239

Minor nit - you don't need the comma after "earlier".

test/CodeGen/x86_32-arguments-iamcu.c

1

Good test!

I think it would be a good idea to add a varargs function & verify that the args do not get marked inreg.

[rnk]

lgtm with the suggested simplification.

lib/CodeGen/TargetInfo.cpp

857

Rather than taking this as a parameter, how about initializing IsMCUABI with getTarget().getTriple().isEnvironmentIAMCU()? Then you can drop a level of parameters.

[mkuper]

lib/CodeGen/TargetInfo.cpp

857

Sure, will do.

test/CodeGen/x86_32-arguments-iamcu.c

1

They do get marked inreg, actually.
The varargs handling for -mregparm - and that means for IAMCU as well - happens on the CG level.

def CC_X86_32_C : CallingConv<[
  ...
  // The first 3 integer arguments, if marked 'inreg' and if the call is not
  // a vararg call, are passed in integer registers.
  **CCIfNotVarArg**<CCIfInReg<CCIfType<[i32], CCAssignToReg<[EAX, EDX, ECX]>>>>,

  ...
]>;

(Yes, this is incredibly ugly. We should probably fix that in a separate patch.)

lib/CodeGen/TargetInfo.cpp

class X86_32ABIInfo : public ABIInfo {
   };
 
   static const unsigned MinABIStackAlignInBytes = 4;
 
   bool IsDarwinVectorABI;
   bool IsRetSmallStructInRegABI;
   bool IsWin32StructABI;
   bool IsSoftFloatABI;
+  bool IsMCUABI;
   unsigned DefaultNumRegisterParameters;
 
   static bool isRegisterSize(unsigned Size) {
     return (Size == 8 || Size == 16 || Size == 32 || Size == 64);
   }
 
   bool isHomogeneousAggregateBaseType(QualType Ty) const override {
     // FIXME: Assumes vectorcall is in use.

 public:
 
   void computeInfo(CGFunctionInfo &FI) const override;
   Address EmitVAArg(CodeGenFunction &CGF, Address VAListAddr,
                     QualType Ty) const override;
 
   X86_32ABIInfo(CodeGen::CodeGenTypes &CGT, bool DarwinVectorABI,
                 bool RetSmallStructInRegABI, bool Win32StructABI,
-                unsigned NumRegisterParameters, bool SoftFloatABI)
+                unsigned NumRegisterParameters, bool SoftFloatABI,
+                bool MCUABI)
     : ABIInfo(CGT), IsDarwinVectorABI(DarwinVectorABI),
       IsRetSmallStructInRegABI(RetSmallStructInRegABI), 
       IsWin32StructABI(Win32StructABI),
-      IsSoftFloatABI(SoftFloatABI),
+      IsSoftFloatABI(SoftFloatABI), IsMCUABI(MCUABI),
       DefaultNumRegisterParameters(NumRegisterParameters) {}
 };
 
 class X86_32TargetCodeGenInfo : public TargetCodeGenInfo {
 public:
   X86_32TargetCodeGenInfo(CodeGen::CodeGenTypes &CGT, bool DarwinVectorABI,
                           bool RetSmallStructInRegABI, bool Win32StructABI,
-                          unsigned NumRegisterParameters, bool SoftFloatABI)
+                          unsigned NumRegisterParameters, bool SoftFloatABI,
+                          bool MCUABI)
       : TargetCodeGenInfo(new X86_32ABIInfo(
             CGT, DarwinVectorABI, RetSmallStructInRegABI, Win32StructABI,
-            NumRegisterParameters, SoftFloatABI)) {}
+            NumRegisterParameters, SoftFloatABI, MCUABI)) {}
 
   static bool isStructReturnInRegABI(
       const llvm::Triple &Triple, const CodeGenOptions &Opts);
 
   void setTargetAttributes(const Decl *D, llvm::GlobalValue *GV,
                            CodeGen::CodeGenModule &CGM) const override;
 
   int getDwarfEHStackPointer(CodeGen::CodeGenModule &CGM) const override {
void X86_32TargetCodeGenInfo::addReturnRegisterOutputs(
   ReturnSlot.setAddress(CGF.Builder.CreateBitCast(ReturnSlot.getAddress(),
                                                   CoerceTy->getPointerTo()));
   ResultRegDests.push_back(ReturnSlot);
 
   rewriteInputConstraintReferences(NumOutputs, 1, AsmString);
 }
 
 /// shouldReturnTypeInRegister - Determine if the given type should be
-/// returned in a register (for the Darwin ABI).
+/// returned in a register (for the Darwin and MCU ABI).
 bool X86_32ABIInfo::shouldReturnTypeInRegister(QualType Ty,
                                                ASTContext &Context) const {
   uint64_t Size = Context.getTypeSize(Ty);
 
   // Type must be register sized.
   if (!isRegisterSize(Size))
     return false;
 
bool X86_32ABIInfo::shouldUseInReg(QualType Ty, CCState &State,
   }
 
   unsigned Size = getContext().getTypeSize(Ty);
   unsigned SizeInRegs = (Size + 31) / 32;
 
   if (SizeInRegs == 0)
     return false;
 
+  if (!IsMCUABI) {
     if (SizeInRegs > State.FreeRegs) {
       State.FreeRegs = 0;
       return false;
     }
+  } else {
+    // The MCU psABI allows passing parameters in-reg even if there are
+    // earlier, parameters that are passed on the stack. Also,
+    // it does not allow passing >8-byte structs in-register,
+    // even if there are 3 free registers available.
+    if (SizeInRegs > State.FreeRegs || SizeInRegs > 2)
+      return false;
+  }
 
   State.FreeRegs -= SizeInRegs;
 
   if (State.CC == llvm::CallingConv::X86_FastCall ||
       State.CC == llvm::CallingConv::X86_VectorCall) {
     if (Size > 32)
       return false;
 
void X86_32ABIInfo::computeInfo(CGFunctionInfo &FI) const {
   CCState State(FI.getCallingConvention());
   if (State.CC == llvm::CallingConv::X86_FastCall)
     State.FreeRegs = 2;
   else if (State.CC == llvm::CallingConv::X86_VectorCall) {
     State.FreeRegs = 2;
     State.FreeSSERegs = 6;
   } else if (FI.getHasRegParm())
     State.FreeRegs = FI.getRegParm();
+  else if (IsMCUABI)
+    State.FreeRegs = 3;
   else
     State.FreeRegs = DefaultNumRegisterParameters;
 
   if (!getCXXABI().classifyReturnType(FI)) {
     FI.getReturnInfo() = classifyReturnType(FI.getReturnType(), State);
   } else if (FI.getReturnInfo().isIndirect()) {
     // The C++ ABI is not aware of register usage, so we have to check if the
     // return value was sret and put it in a register ourselves if appropriate.
bool X86_32TargetCodeGenInfo::isStructReturnInRegABI(
   case CodeGenOptions::SRCK_Default:
     break;
   case CodeGenOptions::SRCK_OnStack:  // -fpcc-struct-return
     return false;
   case CodeGenOptions::SRCK_InRegs:  // -freg-struct-return
     return true;
   }
 
-  if (Triple.isOSDarwin())
+  if (Triple.isOSDarwin() || Triple.isEnvironmentIAMCU())
     return true;
 
   switch (Triple.getOS()) {
   case llvm::Triple::DragonFly:
   case llvm::Triple::FreeBSD:
   case llvm::Triple::OpenBSD:
   case llvm::Triple::Bitrig:
   case llvm::Triple::Win32:

 }
 
 class WinX86_32TargetCodeGenInfo : public X86_32TargetCodeGenInfo {
 public:
   WinX86_32TargetCodeGenInfo(CodeGen::CodeGenTypes &CGT,
         bool DarwinVectorABI, bool RetSmallStructInRegABI, bool Win32StructABI,
         unsigned NumRegisterParameters)
     : X86_32TargetCodeGenInfo(CGT, DarwinVectorABI, RetSmallStructInRegABI,
-        Win32StructABI, NumRegisterParameters, false) {}
+        Win32StructABI, NumRegisterParameters, false, false) {}
 
   void setTargetAttributes(const Decl *D, llvm::GlobalValue *GV,
                            CodeGen::CodeGenModule &CGM) const override;
 
   void getDependentLibraryOption(llvm::StringRef Lib,
                                  llvm::SmallString<24> &Opt) const override {
     Opt = "/DEFAULTLIB:";
     Opt += qualifyWindowsLibrary(Lib);
case llvm::Triple::x86: {
     if (Triple.getOS() == llvm::Triple::Win32) {
       return *(TheTargetCodeGenInfo = new WinX86_32TargetCodeGenInfo(
                    Types, IsDarwinVectorABI, RetSmallStructInRegABI,
                    IsWin32FloatStructABI, CodeGenOpts.NumRegisterParameters));
     } else {
       return *(TheTargetCodeGenInfo = new X86_32TargetCodeGenInfo(
                    Types, IsDarwinVectorABI, RetSmallStructInRegABI,
                    IsWin32FloatStructABI, CodeGenOpts.NumRegisterParameters,
-                   CodeGenOpts.FloatABI == "soft"));
+                   CodeGenOpts.FloatABI == "soft", Triple.isEnvironmentIAMCU()));
     }
   }
 
   case llvm::Triple::x86_64: {
     StringRef ABI = getTarget().getABI();
     X86AVXABILevel AVXLevel = (ABI == "avx512" ? X86AVXABILevel::AVX512 :
                                ABI == "avx" ? X86AVXABILevel::AVX :
                                X86AVXABILevel::None);

test/CodeGen/x86_32-arguments-iamcu.c

+// RUN: %clang_cc1 -w -triple i386-pc-elfiamcu -mfloat-abi soft -emit-llvm -o - %s | FileCheck %s
+
+// CHECK-LABEL: define void @ints(i32 inreg %a, i32 inreg %b, i32 inreg %c, i32 %d)
+void ints(int a, int b, int c, int d) {}
+
+// CHECK-LABEL: define void @floats(float inreg %a, float inreg %b, float inreg %c, float %d)
+void floats(float a, float b, float c, float d) {}
+
+// CHECK-LABEL: define void @mixed(i32 inreg %a, float inreg %b, i32 inreg %c, float %d)
+void mixed(int a, float b, int c, float d) {}
+
+// CHECK-LABEL: define void @doubles(double inreg %d1, double %d2)
+void doubles(double d1, double d2) {}
+
+// CHECK-LABEL: define void @mixedDoubles(i32 inreg %a, double inreg %d1)
+void mixedDoubles(int a, double d1) {}
+
+typedef struct st4_t {
+  int a;
+} st4_t;
+
+typedef struct st5_t {
+  int a;
+  char b;
+} st5_t;
+
+typedef  struct st12_t {
+  int a;
+  int b;
+  int c;
+} st12_t;
+
+// CHECK-LABEL: define void @smallStructs(i32 inreg %st1.coerce, i32 inreg %st2.coerce, i32 inreg %st3.coerce)
+void smallStructs(st4_t st1, st4_t st2, st4_t st3) {}
+
+// CHECK-LABEL: define void @paddedStruct(i32 inreg %i1, i32 inreg %st.coerce0, i32 inreg %st.coerce1, i32 %st4.0)
+void paddedStruct(int i1, st5_t st, st4_t st4) {}
+
+// CHECK-LABEL: define void @largeStruct(i32 %st.0, i32 %st.1, i32 %st.2)
+void largeStruct(st12_t st) {}
+
+// CHECK-LABEL: define void @largeStructMiddle(i32 inreg %i1, i32 %st.0, i32 %st.1, i32 %st.2, i32 inreg %i2, i32 inreg %i3)
+void largeStructMiddle(int i1, st12_t st, int i2, int i3) {}
+
+// CHECK-LABEL: define i32 @retSmallStruct(i32 inreg %r.coerce)
+st4_t retSmallStruct(st4_t r) { return r; }
+
+// CHECK-LABEL: define i64 @retPaddedStruct(i32 inreg %r.coerce0, i32 inreg %r.coerce1)
+st5_t retPaddedStruct(st5_t r) { return r; }
+
+// CHECK-LABEL: define void @retLargeStruct(%struct.st12_t* inreg noalias sret %agg.result, i32 inreg %i1, i32 %r.0, i32 %r.1, i32 %r.2)
+st12_t retLargeStruct(int i1, st12_t r) { return r; }