Hello tech list, This is a diff for base-clang. It would change the powerpc target to return small structs in registers r3 and r4. This would fix an incompatibility with gcc in OpenBSD macppc. I fear that if I commit the diff, I might break snapshot builds. I am looking for help.
I posted the diff upstream: https://reviews.llvm.org/D73290 Then backported it to ports-clang and mailed it to ports@: https://marc.info/?l=openbsd-ports&m=158026852003182&w=2 This is the same diff for base-clang. Apply diff in /usr/src/gnu/llvm, then build clang like # cd /usr/src/gnu/usr.bin/clang # make obj # make # make install My macppc machine, an iMac G3 with 512M RAM, is too slow to build llvm and clang. The iMac is now in the 11th day of building ports-clang (but I turned it off overnight), and within the last 200 of over 4400 targets. After a .cpp file got stuck while using over 800M swap (on hard disk), I set vm.swapencrypt.enable=0 and switched to swap on NFS. (For contrast, my amd64 desktop built ports-clang in about 2 hours.) cwen@ built ports-clang with my diff on a G4 in "29 hours". rgc <rgci...@disroot.org> built base-clang with the diff in this mail. Both got good results from my small test programs in the attachment (sret-examples.tar.gz) to my ports@ mail. The diff affects all platforms (if they build clang), so if the diff would break clang, it might break arches other than macppc. I built and installed base-clang with this diff on amd64 (using make -j4 to speed up the build). Then, with the patched clang, I built an amd64 release(8) of base and xenocara. I used my new install66.iso to install a new amd64 virtual machine, including the patched clang. We build most of OpenBSD macppc with base-gcc, but we use base-clang for at least clang itself. I don't know whether the patched base-clang can still build base-clang, whether the patch would break the base build on macppc. The patch adds -maix-struct-return and -msvr4-struct-return: $ clang -msvr-struct-return -x c /dev/null clang: error: unknown argument '-msvr-struct-return', did you mean '-msvr4-struct-return'? $ clang -msvr4-struct-return -x c /dev/null clang: error: unsupported option '-msvr4-struct-return' for target 'amd64-unknown-openbsd6.6' On OpenBSD macppc, gcc defaults to -msvr4-struct-return (to return small structs in registers r3 and r4), but clang without the patch always acts like gcc -maix-struct-return (to return small structs in memory through a sret pointer). The patch adds the options and changes the default to -msvr4-struct-return on OpenBSD (and other ELF except Linux). The options work only on 32-bit powerpc. When the patch returns a struct in registers, it coerces the struct to an integer; this changes the LLVM IR from clang to not use a sret pointer. The option handling for -m{aix,svr4}-struct-return is mostly a copy of that for -f{pcc,reg}-struct-return on i386. --George Index: tools/clang/include/clang/Driver/Options.td =================================================================== RCS file: /cvs/src/gnu/llvm/tools/clang/include/clang/Driver/Options.td,v retrieving revision 1.11 diff -u -p -r1.11 Options.td --- tools/clang/include/clang/Driver/Options.td 23 Jun 2019 22:05:15 -0000 1.11 +++ tools/clang/include/clang/Driver/Options.td 30 Jan 2020 01:13:29 -0000 @@ -2238,6 +2238,12 @@ def mlongcall: Flag<["-"], "mlongcall">, Group<m_ppc_Features_Group>; def mno_longcall : Flag<["-"], "mno-longcall">, Group<m_ppc_Features_Group>; +def maix_struct_return : Flag<["-"], "maix-struct-return">, + Group<m_Group>, Flags<[CC1Option]>, + HelpText<"Return all structs in memory (PPC32 only)">; +def msvr4_struct_return : Flag<["-"], "msvr4-struct-return">, + Group<m_Group>, Flags<[CC1Option]>, + HelpText<"Return small structs in registers (PPC32 only)">; def mvx : Flag<["-"], "mvx">, Group<m_Group>; def mno_vx : Flag<["-"], "mno-vx">, Group<m_Group>; Index: tools/clang/lib/CodeGen/TargetInfo.cpp =================================================================== RCS file: /cvs/src/gnu/llvm/tools/clang/lib/CodeGen/TargetInfo.cpp,v retrieving revision 1.1.1.7 diff -u -p -r1.1.1.7 TargetInfo.cpp --- tools/clang/lib/CodeGen/TargetInfo.cpp 23 Jun 2019 21:37:39 -0000 1.1.1.7 +++ tools/clang/lib/CodeGen/TargetInfo.cpp 30 Jan 2020 01:13:30 -0000 @@ -4092,12 +4092,24 @@ namespace { /// PPC32_SVR4_ABIInfo - The 32-bit PowerPC ELF (SVR4) ABI information. class PPC32_SVR4_ABIInfo : public DefaultABIInfo { bool IsSoftFloatABI; + bool IsRetSmallStructInRegABI; CharUnits getParamTypeAlignment(QualType Ty) const; public: - PPC32_SVR4_ABIInfo(CodeGen::CodeGenTypes &CGT, bool SoftFloatABI) - : DefaultABIInfo(CGT), IsSoftFloatABI(SoftFloatABI) {} + PPC32_SVR4_ABIInfo(CodeGen::CodeGenTypes &CGT, bool SoftFloatABI, + bool RetSmallStructInRegABI) + : DefaultABIInfo(CGT), IsSoftFloatABI(SoftFloatABI), + IsRetSmallStructInRegABI(RetSmallStructInRegABI) {} + + ABIArgInfo classifyReturnType(QualType RetTy) const; + + void computeInfo(CGFunctionInfo &FI) const override { + if (!getCXXABI().classifyReturnType(FI)) + FI.getReturnInfo() = classifyReturnType(FI.getReturnType()); + for (auto &I : FI.arguments()) + I.info = classifyArgumentType(I.type); + } Address EmitVAArg(CodeGenFunction &CGF, Address VAListAddr, QualType Ty) const override; @@ -4105,8 +4117,13 @@ public: class PPC32TargetCodeGenInfo : public TargetCodeGenInfo { public: - PPC32TargetCodeGenInfo(CodeGenTypes &CGT, bool SoftFloatABI) - : TargetCodeGenInfo(new PPC32_SVR4_ABIInfo(CGT, SoftFloatABI)) {} + PPC32TargetCodeGenInfo(CodeGenTypes &CGT, bool SoftFloatABI, + bool RetSmallStructInRegABI) + : TargetCodeGenInfo(new PPC32_SVR4_ABIInfo(CGT, SoftFloatABI, + RetSmallStructInRegABI)) {} + + static bool isStructReturnInRegABI(const llvm::Triple &Triple, + const CodeGenOptions &Opts); int getDwarfEHStackPointer(CodeGen::CodeGenModule &M) const override { // This is recovered from gcc output. @@ -4142,6 +4159,34 @@ CharUnits PPC32_SVR4_ABIInfo::getParamTy return CharUnits::fromQuantity(4); } +ABIArgInfo PPC32_SVR4_ABIInfo::classifyReturnType(QualType RetTy) const { + uint64_t Size; + + // -msvr4-struct-return puts small aggregates in GPR3 and GPR4. + if (isAggregateTypeForABI(RetTy) && IsRetSmallStructInRegABI && + (Size = getContext().getTypeSize(RetTy)) <= 64) { + // System V ABI (1995), page 3-22, specified: + // > A structure or union whose size is less than or equal to 8 bytes + // > shall be returned in r3 and r4, as if it were first stored in the + // > 8-byte aligned memory area and then the low addressed word were + // > loaded into r3 and the high-addressed word into r4. Bits beyond + // > the last member of the structure or union are not defined. + // + // GCC for big-endian PPC32 inserts the pad before the first member, + // not "beyond the last member" of the struct. To stay compatible + // with GCC, we coerce the struct to an integer of the same size. + // LLVM will extend it and return i32 in r3, or i64 in r3:r4. + if (Size == 0) + return ABIArgInfo::getIgnore(); + else { + llvm::Type *CoerceTy = llvm::Type::getIntNTy(getVMContext(), Size); + return ABIArgInfo::getDirect(CoerceTy); + } + } + + return DefaultABIInfo::classifyReturnType(RetTy); +} + // TODO: this implementation is now likely redundant with // DefaultABIInfo::EmitVAArg. Address PPC32_SVR4_ABIInfo::EmitVAArg(CodeGenFunction &CGF, Address VAList, @@ -4299,6 +4344,25 @@ Address PPC32_SVR4_ABIInfo::EmitVAArg(Co return Result; } +bool PPC32TargetCodeGenInfo::isStructReturnInRegABI( + const llvm::Triple &Triple, const CodeGenOptions &Opts) { + assert(Triple.getArch() == llvm::Triple::ppc); + + switch (Opts.getStructReturnConvention()) { + case CodeGenOptions::SRCK_Default: + break; + case CodeGenOptions::SRCK_OnStack: // -maix-struct-return + return false; + case CodeGenOptions::SRCK_InRegs: // -msvr4-struct-return + return true; + } + + if (Triple.isOSBinFormatELF() && !Triple.isOSLinux()) + return true; + + return false; +} + bool PPC32TargetCodeGenInfo::initDwarfEHRegSizeTable(CodeGen::CodeGenFunction &CGF, llvm::Value *Address) const { @@ -9330,9 +9394,13 @@ const TargetCodeGenInfo &CodeGenModule:: return SetCGInfo(new ARMTargetCodeGenInfo(Types, Kind)); } - case llvm::Triple::ppc: + case llvm::Triple::ppc: { + bool RetSmallStructInRegABI = + PPC32TargetCodeGenInfo::isStructReturnInRegABI(Triple, CodeGenOpts); return SetCGInfo( - new PPC32TargetCodeGenInfo(Types, CodeGenOpts.FloatABI == "soft")); + new PPC32TargetCodeGenInfo(Types, CodeGenOpts.FloatABI == "soft", + RetSmallStructInRegABI)); + } case llvm::Triple::ppc64: if (Triple.isOSBinFormatELF()) { PPC64_SVR4_ABIInfo::ABIKind Kind = PPC64_SVR4_ABIInfo::ELFv1; Index: tools/clang/lib/Driver/ToolChains/Clang.cpp =================================================================== RCS file: /cvs/src/gnu/llvm/tools/clang/lib/Driver/ToolChains/Clang.cpp,v retrieving revision 1.20 diff -u -p -r1.20 Clang.cpp --- tools/clang/lib/Driver/ToolChains/Clang.cpp 25 Oct 2019 00:40:56 -0000 1.20 +++ tools/clang/lib/Driver/ToolChains/Clang.cpp 30 Jan 2020 01:13:30 -0000 @@ -3870,6 +3870,19 @@ void Clang::ConstructJob(Compilation &C, CmdArgs.push_back(A->getValue()); } + if (Arg *A = Args.getLastArg(options::OPT_maix_struct_return, + options::OPT_msvr4_struct_return)) { + if (TC.getArch() != llvm::Triple::ppc) { + D.Diag(diag::err_drv_unsupported_opt_for_target) + << A->getSpelling() << RawTriple.str(); + } else if (A->getOption().matches(options::OPT_maix_struct_return)) { + CmdArgs.push_back("-maix-struct-return"); + } else { + assert(A->getOption().matches(options::OPT_msvr4_struct_return)); + CmdArgs.push_back("-msvr4-struct-return"); + } + } + if (Arg *A = Args.getLastArg(options::OPT_fpcc_struct_return, options::OPT_freg_struct_return)) { if (TC.getArch() != llvm::Triple::x86) { Index: tools/clang/lib/Frontend/CompilerInvocation.cpp =================================================================== RCS file: /cvs/src/gnu/llvm/tools/clang/lib/Frontend/CompilerInvocation.cpp,v retrieving revision 1.4 diff -u -p -r1.4 CompilerInvocation.cpp --- tools/clang/lib/Frontend/CompilerInvocation.cpp 23 Jun 2019 22:05:15 -0000 1.4 +++ tools/clang/lib/Frontend/CompilerInvocation.cpp 30 Jan 2020 01:13:30 -0000 @@ -1199,11 +1199,18 @@ static bool ParseCodeGenArgs(CodeGenOpti Diags.Report(diag::err_drv_invalid_value) << A->getAsString(Args) << Val; } - if (Arg *A = Args.getLastArg(OPT_fpcc_struct_return, OPT_freg_struct_return)) { - if (A->getOption().matches(OPT_fpcc_struct_return)) { + // X86_32 has -fppc-struct-return and -freg-struct-return. + // PPC32 has -maix-struct-return and -msvr4-struct-return. + if (Arg *A = + Args.getLastArg(OPT_fpcc_struct_return, OPT_freg_struct_return, + OPT_maix_struct_return, OPT_msvr4_struct_return)) { + const Option &O = A->getOption(); + if (O.matches(OPT_fpcc_struct_return) || + O.matches(OPT_maix_struct_return)) { Opts.setStructReturnConvention(CodeGenOptions::SRCK_OnStack); } else { - assert(A->getOption().matches(OPT_freg_struct_return)); + assert(O.matches(OPT_freg_struct_return) || + O.matches(OPT_msvr4_struct_return)); Opts.setStructReturnConvention(CodeGenOptions::SRCK_InRegs); } }
