[X86] Enable soft float ABI for x86

[mkuper]

Summary

The Intel MCU psABI is a new soft-float ABI, based on the IA32 psABI.
The document describing the ABI can be found here: https://github.com/hjl-tools/x86-psABI/wiki/iamcu-psABI-0.7.pdf

Perhaps the biggest difference between the IA32 and MCU ABIs is that the MCU ABI is soft-float.
This patch makes the x86-32 ABI code respect "-mfloat-abi soft" and generate float inreg arguments.

This is the first patch in a series - there will be separate patches to add the "-miamcu" driver option, as well as more ABI adjustments to actually make it work.

(I'll clean up the one-letter variable names in a separate commit.)

[rnk]

lgtm Sorry, took me a while to read the document and understand why you want float inreg.

I think we overload LLVM inreg to mean "put this float / double in an SSE register", but I think it's reasonable for it to mean "put it in an integer register" when FP support is disabled in the subtarget.

[mkuper]

It's ok, thanks a lot for taking the time to review it!

lib/CodeGen/TargetInfo.cpp

enum Class {
     Float
   };
 
   static const unsigned MinABIStackAlignInBytes = 4;
 
   bool IsDarwinVectorABI;
   bool IsSmallStructInRegABI;
   bool IsWin32StructABI;
+  bool IsSoftFloatABI;
   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 d, bool p, bool w,
-                unsigned r)
+                unsigned r, bool s)
     : ABIInfo(CGT), IsDarwinVectorABI(d), IsSmallStructInRegABI(p),
-      IsWin32StructABI(w), DefaultNumRegisterParameters(r) {}
+      IsWin32StructABI(w), DefaultNumRegisterParameters(r),
+      IsSoftFloatABI(s) {}
 };
 
 class X86_32TargetCodeGenInfo : public TargetCodeGenInfo {
 public:
   X86_32TargetCodeGenInfo(CodeGen::CodeGenTypes &CGT,
-      bool d, bool p, bool w, unsigned r)
-    :TargetCodeGenInfo(new X86_32ABIInfo(CGT, d, p, w, r)) {}
+      bool d, bool p, bool w, unsigned r, bool s)
+    :TargetCodeGenInfo(new X86_32ABIInfo(CGT, d, p, w, r, s)) {}
 
   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 {
if (K == BuiltinType::Float || K == BuiltinType::Double)
       return Float;
   }
   return Integer;
 }
 
 bool X86_32ABIInfo::shouldUseInReg(QualType Ty, CCState &State,
                                    bool &NeedsPadding) const {
   NeedsPadding = false;
-  Class C = classify(Ty);
+  if (!IsSoftFloatABI) {
+    Class C = classify(Ty);  
     if (C == Float)
       return false;
+  }
   
   unsigned Size = getContext().getTypeSize(Ty);
   unsigned SizeInRegs = (Size + 31) / 32;
 
   if (SizeInRegs == 0)
     return false;
 
   if (SizeInRegs > State.FreeRegs) {
     State.FreeRegs = 0;
static std::string qualifyWindowsLibrary(llvm::StringRef Lib) {
   ArgStr += Quote ? "\"" : "";
   return ArgStr;
 }
 
 class WinX86_32TargetCodeGenInfo : public X86_32TargetCodeGenInfo {
 public:
   WinX86_32TargetCodeGenInfo(CodeGen::CodeGenTypes &CGT,
         bool d, bool p, bool w, unsigned RegParms)
-    : X86_32TargetCodeGenInfo(CGT, d, p, w, RegParms) {}
+    : X86_32TargetCodeGenInfo(CGT, d, p, w, RegParms, 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, IsSmallStructInRegABI,
                    IsWin32FloatStructABI, CodeGenOpts.NumRegisterParameters));
     } else {
       return *(TheTargetCodeGenInfo = new X86_32TargetCodeGenInfo(
                    Types, IsDarwinVectorABI, IsSmallStructInRegABI,
-                   IsWin32FloatStructABI, CodeGenOpts.NumRegisterParameters));
+                   IsWin32FloatStructABI, CodeGenOpts.NumRegisterParameters,
+                   CodeGenOpts.FloatABI == "soft"));
     }
   }
 
   case llvm::Triple::x86_64: {
     StringRef ABI = getTarget().getABI();
     X86AVXABILevel AVXLevel = (ABI == "avx512" ? X86AVXABILevel::AVX512 :
                                ABI == "avx" ? X86AVXABILevel::AVX :
                                X86AVXABILevel::None);

test/CodeGen/x86-soft-float.c

+// RUN: %clang_cc1 -triple i386-unknown-unknown -mregparm 3 -emit-llvm %s -o - | FileCheck %s -check-prefix=HARD
+// RUN: %clang_cc1 -triple i386-unknown-unknown -mregparm 3 -mfloat-abi soft -emit-llvm %s -o - | FileCheck %s -check-prefix=SOFT
+
+// HARD: define void @f1(float %a)
+// SOFT: define void @f1(float inreg %a)
+void f1(float a) {}