[CSKY 1/n] Add basic stub or infra of csky backend

[zixuan-wu]

Summary

This patch introduce files that just enough for lib/Target/CSKY to compile.
Notably a basic CSKYTargetMachine and CSKYTargetInfo.

[zixuan-wu]

Gentle ping...
BTW, @lattner would you know who is the decision maker that can approve a new target and review related commit?

[lattner]

The general process is here: https://llvm.org/docs/DeveloperPolicy.html#adding-a-new-target

I'm sorry that I'm preoccupied with the devmtg this week, but please ping me next week if you're not getting traction, thanks!

[theraven]

Mostly boilerplate that looks fine, a few minor nits.

llvm/lib/Target/CSKY/CSKYTargetMachine.cpp

32

Minor nit, but hopefully anyone reading this knows what e means from reading the LangRef. It would be more useful for this comment to give a summary of what is happening here specifically, for example 'CSky is always little endian with a 4-byte aligned stack'

36

If the endian and stack alignment are the same for every instance of this back end, you don't need to add them separately. The same is true for all of the things after the mangling flag.

38

Does CSky really support all of the manglings that this can return? Including Windows x86 mangling? If not, please add some asserts to validate that it's a sane value.

71

Why make this a separate function instead of just writing this on line 84:

(RM.hasValue() ? *RM : Reloc::Static),

[zixuan-wu]

In D88466#2318573, @lattner wrote:

The general process is here: https://llvm.org/docs/DeveloperPolicy.html#adding-a-new-target

I'm sorry that I'm preoccupied with the devmtg this week, but please ping me next week if you're not getting traction, thanks!

The general process is clear but there is not info about who is main reviewer can approve threading patches.

[zixuan-wu]

Address comments.

[theraven]

I lost track of the mailing list discussions, but assuming that there is consensus to accept this back end I am happy with the structure of the initial code, the size of the contributed diffs, and the engagement from the maintainer.

[zixuan-wu]

In D88466#2320949, @theraven wrote:

I lost track of the mailing list discussions, but assuming that there is consensus to accept this back end I am happy with the structure of the initial code, the size of the contributed diffs, and the engagement from the maintainer.

Thank you!

[Arfrever]

llvm/lib/Target/CSKY/TargetInfo/CSKYTargetInfo.cpp

19

This needs LLVM_EXTERNAL_VISIBILITY:

extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeCSKYTargetInfo() {

To avoid error:

FAILED: lib/libLTO.so.12 
: && /usr/bin/x86_64-pc-linux-gnu-g++ -m32 -fPIC -march=native -O2  -pipe -fPIC -fvisibility-inlines-hidden -Werror=date-time -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -pedantic -Wno-long-long -Wimplicit-fallthrough -Wno-maybe-uninitialized -Wno-class-memaccess -Wno-redundant-move -Wno-noexcept-type -Wdelete-non-virtual-dtor -Wsuggest-override -Wno-comment -fdiagnostics-color -ffunction-sections -fdata-sections  -fuse-ld=bfd -Wl,-O1 -Wl,--as-needed -Wl,--defsym=__gentoo_check_ldflags__=0 -Wl,--gc-sections -Wl,--sort-common -Wl,-z,now -Wl,-z,defs -Wl,-z,nodelete   -Wl,-rpath-link,/var/tmp/portage/sys-devel/llvm-12.0.0.9999/work/llvm_build-abi_x86_32.x86/./lib  -Wl,-O3 -Wl,--gc-sections  -Wl,--version-script,"/var/tmp/portage/sys-devel/llvm-12.0.0.9999/work/llvm_build-abi_x86_32.x86/tools/lto/LTO.exports" -shared -Wl,-soname,libLTO.so.12 -o lib/libLTO.so.12 tools/lto/CMakeFiles/LTO.dir/LTODisassembler.cpp.o tools/lto/CMakeFiles/LTO.dir/lto.cpp.o  -Wl,-rpath,"\$ORIGIN/../lib"  lib/libLLVM-12git.so && :
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/../../../../x86_64-pc-linux-gnu/bin/ld.bfd: tools/lto/CMakeFiles/LTO.dir/lto.cpp.o: in function `lto_initialize()':
lto.cpp:(.text._ZL14lto_initializev+0x7e): undefined reference to `LLVMInitializeCSKYTargetInfo'
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/../../../../x86_64-pc-linux-gnu/bin/ld.bfd: lto.cpp:(.text._ZL14lto_initializev+0xe2): undefined reference to `LLVMInitializeCSKYTargetInfo'
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/../../../../x86_64-pc-linux-gnu/bin/ld.bfd: tools/lto/CMakeFiles/LTO.dir/LTODisassembler.cpp.o: in function `lto_initialize_disassembler':
LTODisassembler.cpp:(.text.lto_initialize_disassembler+0x49): undefined reference to `LLVMInitializeCSKYTargetInfo'
collect2: error: ld returned 1 exit status

[zixuan-wu]

llvm/lib/Target/CSKY/TargetInfo/CSKYTargetInfo.cpp

19

This needs LLVM_EXTERNAL_VISIBILITY:

extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeCSKYTargetInfo() {

To avoid error:

FAILED: lib/libLTO.so.12 
: && /usr/bin/x86_64-pc-linux-gnu-g++ -m32 -fPIC -march=native -O2  -pipe -fPIC -fvisibility-inlines-hidden -Werror=date-time -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -pedantic -Wno-long-long -Wimplicit-fallthrough -Wno-maybe-uninitialized -Wno-class-memaccess -Wno-redundant-move -Wno-noexcept-type -Wdelete-non-virtual-dtor -Wsuggest-override -Wno-comment -fdiagnostics-color -ffunction-sections -fdata-sections  -fuse-ld=bfd -Wl,-O1 -Wl,--as-needed -Wl,--defsym=__gentoo_check_ldflags__=0 -Wl,--gc-sections -Wl,--sort-common -Wl,-z,now -Wl,-z,defs -Wl,-z,nodelete   -Wl,-rpath-link,/var/tmp/portage/sys-devel/llvm-12.0.0.9999/work/llvm_build-abi_x86_32.x86/./lib  -Wl,-O3 -Wl,--gc-sections  -Wl,--version-script,"/var/tmp/portage/sys-devel/llvm-12.0.0.9999/work/llvm_build-abi_x86_32.x86/tools/lto/LTO.exports" -shared -Wl,-soname,libLTO.so.12 -o lib/libLTO.so.12 tools/lto/CMakeFiles/LTO.dir/LTODisassembler.cpp.o tools/lto/CMakeFiles/LTO.dir/lto.cpp.o  -Wl,-rpath,"\$ORIGIN/../lib"  lib/libLLVM-12git.so && :
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/../../../../x86_64-pc-linux-gnu/bin/ld.bfd: tools/lto/CMakeFiles/LTO.dir/lto.cpp.o: in function `lto_initialize()':
lto.cpp:(.text._ZL14lto_initializev+0x7e): undefined reference to `LLVMInitializeCSKYTargetInfo'
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/../../../../x86_64-pc-linux-gnu/bin/ld.bfd: lto.cpp:(.text._ZL14lto_initializev+0xe2): undefined reference to `LLVMInitializeCSKYTargetInfo'
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/../../../../x86_64-pc-linux-gnu/bin/ld.bfd: tools/lto/CMakeFiles/LTO.dir/LTODisassembler.cpp.o: in function `lto_initialize_disassembler':
LTODisassembler.cpp:(.text.lto_initialize_disassembler+0x49): undefined reference to `LLVMInitializeCSKYTargetInfo'
collect2: error: ld returned 1 exit status

Sorry to miss the notify.
It's fixed at https://reviews.llvm.org/rGcddd3faf5debdfd2c09bb5b723f579fa8c8d5027.

llvm/CODE_OWNERS.TXT

 
 N: Jake Ehrlich
 E: [e-mail]
 D: llvm-objcopy (tools/llvm-objcopy)
 
 N: Martin Storsjö
 E: [e-mail]
 D: MinGW
+
+N: Zi Xuan Wu (Zeson)
+E: [e-mail]
+D: C-SKY backend (lib/Target/CSKY/*)

llvm/docs/CompilerWriterInfo.rst

 ------
 
 Refer to :doc:`AMDGPUUsage` for additional documentation.
 
 RISC-V
 ------
 * `RISC-V User-Level ISA Specification <https://riscv.org/specifications/>`_
 
+C-SKY
+------
+* `C-SKY Architecture User Guide <https://github.com/c-sky/csky-doc/blob/master/CSKY%20Architecture%20user_guide.pdf>`_
+* `C-SKY V2 ABI <https://github.com/c-sky/csky-doc/blob/master/C-SKY_V2_CPU_Applications_Binary_Interface_Standards_Manual.pdf>`_
+
 SPARC
 -----
 
 * `SPARC standards <http://sparc.org/standards>`_
 * `SPARC V9 ABI <http://sparc.org/standards/64.psabi.1.35.ps.Z>`_
 * `SPARC V8 ABI <http://sparc.org/standards/psABI3rd.pdf>`_
 
 SystemZ

llvm/lib/Target/CSKY/CMakeLists.txt

+add_llvm_target(CSKYCodeGen
+  CSKYTargetMachine.cpp
+  )
+
+add_subdirectory(TargetInfo)

llvm/lib/Target/CSKY/CSKYTargetMachine.h

+//===--- CSKYTargetMachine.h - Define TargetMachine for CSKY ----*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This file declares the CSKY specific subclass of TargetMachine.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIB_TARGET_CSKY_CSKYTARGETMACHINE_H
+#define LLVM_LIB_TARGET_CSKY_CSKYTARGETMACHINE_H
+
+#include "llvm/IR/DataLayout.h"
+#include "llvm/Target/TargetMachine.h"
+
+namespace llvm {
+
+class CSKYTargetMachine : public LLVMTargetMachine {
+  std::unique_ptr<TargetLoweringObjectFile> TLOF;
+
+public:
+  CSKYTargetMachine(const Target &T, const Triple &TT, StringRef CPU,
+                    StringRef FS, const TargetOptions &Options,
+                    Optional<Reloc::Model> RM, Optional<CodeModel::Model> CM,
+                    CodeGenOpt::Level OL, bool JIT);
+
+  TargetPassConfig *createPassConfig(PassManagerBase &PM) override;
+
+  TargetLoweringObjectFile *getObjFileLowering() const override {
+    return TLOF.get();
+  }
+};
+} // namespace llvm
+
+#endif

llvm/lib/Target/CSKY/CSKYTargetMachine.cpp

+//===--- CSKYTargetMachine.cpp - Define TargetMachine for CSKY ------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// Implements the info about CSKY target spec.
+//
+//===----------------------------------------------------------------------===//
+
+#include "CSKYTargetMachine.h"
+#include "TargetInfo/CSKYTargetInfo.h"
+#include "llvm/CodeGen/TargetLoweringObjectFileImpl.h"
+#include "llvm/CodeGen/TargetPassConfig.h"
+#include "llvm/Support/TargetRegistry.h"
+
+using namespace llvm;
+
+extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeCSKYTarget() {
+  RegisterTargetMachine<CSKYTargetMachine> X(getTheCSKYTarget());
+}
+
+static std::string computeDataLayout(const Triple &TT) {
+  std::string Ret;
+
+  // Only support little endian for now.
+  // TODO: Add support for big endian.
+  Ret += "e";
+
+  // CSKY is always 32-bit target with the CSKYv2 ABI as prefer now.
+  // It's a 4-byte aligned stack with ELF mangling only.
+  Ret += "-m:e-S32-p:32:32-i32:32:32-i64:32:32-f32:32:32-f64:32:32-v64:32:32"
+         "-v128:32:32-a:0:32-Fi32-n32";
+
+  return Ret;
+}
+
+CSKYTargetMachine::CSKYTargetMachine(const Target &T, const Triple &TT,
+                                     StringRef CPU, StringRef FS,
+                                     const TargetOptions &Options,
+                                     Optional<Reloc::Model> RM,
+                                     Optional<CodeModel::Model> CM,
+                                     CodeGenOpt::Level OL, bool JIT)
+    : LLVMTargetMachine(T, computeDataLayout(TT), TT, CPU, FS, Options,
+                        !RM.hasValue() ? Reloc::Static : *RM,
+                        getEffectiveCodeModel(CM, CodeModel::Small), OL),
+      TLOF(std::make_unique<TargetLoweringObjectFileELF>()) {
+  initAsmInfo();
+}
+
+namespace {
+class CSKYPassConfig : public TargetPassConfig {
+public:
+  CSKYPassConfig(CSKYTargetMachine &TM, PassManagerBase &PM)
+      : TargetPassConfig(TM, PM) {}
+
+  CSKYTargetMachine &getCSKYTargetMachine() const {
+    return getTM<CSKYTargetMachine>();
+  }
+};
+
+} // namespace
+
+TargetPassConfig *CSKYTargetMachine::createPassConfig(PassManagerBase &PM) {
+  return new CSKYPassConfig(*this, PM);
+}

llvm/lib/Target/CSKY/LLVMBuild.txt

+;===----- ./lib/Target/CSKY/LLVMBuild.txt ----------------------*- Conf -*--===;
+;
+; 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
+;
+;===------------------------------------------------------------------------===;
+;
+; This is an LLVMBuild description file for the components in this subdirectory.
+;
+; For more information on the LLVMBuild system, please see:
+;
+;   http://llvm.org/docs/LLVMBuild.html
+;
+;===------------------------------------------------------------------------===;
+
+[common]
+subdirectories = TargetInfo
+
+[component_0]
+type = TargetGroup
+name = CSKY
+parent = Target
+
+[component_1]
+type = Library
+name = CSKYCodeGen
+parent = CSKY
+required_libraries = Core CodeGen CSKYInfo Support Target
+add_to_library_groups = CSKY

llvm/lib/Target/CSKY/TargetInfo/CMakeLists.txt

+add_llvm_library(LLVMCSKYInfo
+  CSKYTargetInfo.cpp
+  )

llvm/lib/Target/CSKY/TargetInfo/CSKYTargetInfo.h

+//===-- CSKYTargetInfo.cpp - CSKY Target Implementation -------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIB_TARGET_CSKY_TARGETINFO_CSKYTARGETINFO_H
+#define LLVM_LIB_TARGET_CSKY_TARGETINFO_CSKYTARGETINFO_H
+
+namespace llvm {
+
+class Target;
+
+Target &getTheCSKYTarget();
+
+} // namespace llvm
+
+#endif // LLVM_LIB_TARGET_CSKY_TARGETINFO_CSKYTARGETINFO_H

llvm/lib/Target/CSKY/TargetInfo/CSKYTargetInfo.cpp

+//===-- CSKYTargetInfo.cpp - CSKY Target Implementation -------------------===//
+//
+// 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 "TargetInfo/CSKYTargetInfo.h"
+#include "llvm/Support/TargetRegistry.h"
+using namespace llvm;
+
+Target &llvm::getTheCSKYTarget() {
+  static Target TheCSKYTarget;
+  return TheCSKYTarget;
+}
+
+extern "C" void LLVMInitializeCSKYTargetInfo() {
+  RegisterTarget<Triple::csky> X(getTheCSKYTarget(), "csky", "C-SKY", "CSKY");
+}
+
+// FIXME: Temporary stub - this function must be defined for linking
+// to succeed and will be called unconditionally by llc, so must be a no-op.
+// Remove once this function is properly implemented.
+extern "C" void LLVMInitializeCSKYTargetMC() {}

llvm/lib/Target/CSKY/TargetInfo/LLVMBuild.txt

+;===-- ./lib/Target/CSKY/TargetInfo/LLVMBuild.txt --------------*- Conf -*--===;
+;
+; 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
+;
+;===------------------------------------------------------------------------===;
+;
+; This is an LLVMBuild description file for the components in this subdirectory.
+;
+; For more information on the LLVMBuild system, please see:
+;
+;   http://llvm.org/docs/LLVMBuild.html
+;
+;===------------------------------------------------------------------------===;
+
+[component_0]
+type = Library
+name = CSKYInfo
+parent = CSKY
+required_libraries = Support
+add_to_library_groups = CSKY

llvm/lib/Target/LLVMBuild.txt

 [common]
 subdirectories =
  AArch64
  AMDGPU
  ARC
  ARM
  AVR
  BPF
+ CSKY
  Hexagon
  Lanai
  MSP430
  Mips
  NVPTX
  PowerPC
  RISCV
  Sparc