[RISCV][MC] Delete unnecessary code section align

[StephenFan]

Summary

Since RISCVELFTargetObjectFile does not inherit RISCVMCObjectFileInfo,
the alignment of code section is always 4 even if c extension was enabled.
If c extension was enabled, the nop instruction is 2 bytes, which will
make the assember to emit a code align fixup.

[MaskRay]

Err, multiple virtual inheritance is tricky. Anyway to avoid it?

[craig.topper]

Could we make the text segment alignment a member variable of MCObjectInfo instead of needing to use a virtual method in MCObjectInfo? Then we'd just need to assign that member from RISCVMCObjectInfo and
RISCVTargetObjectFile.

[StephenFan]

1. Add setTextSectionAlignment function to allow target set text section alignment
2. Set RISCV's text section alignment when initialize RISCVELFTargetObjectFile
3. Set RISCV's text section alignment when create RISCVMCObjectFileInfo

[StephenFan]

rebase

[craig.topper]

llvm/lib/Target/RISCV/RISCVSubtarget.cpp

22

This is the only change in this file. Is it needed?

llvm/lib/Target/RISCV/RISCVTargetObjectFile.h

13

There no changes to this file other than include, is it really needed here?

[StephenFan]

Remove header file.

[craig.topper]

LGTM

[MaskRay]

llvm/test/CodeGen/RISCV/unnecessary-code-align.ll

5 ↗

(On Diff #440837)

; CHECK:      Relocations [
; CHECK-NEXT: ]

[StephenFan]

Remove CHECK-NOT.

[MaskRay]

If this tests alignment, you probably want to check llvm-readelf -S -r output. -S for the Al column. -r is to check there is no relocation.

[StephenFan]

Check llvm-readelf -S -r instead of llvm-readobj -r.

llvm/include/llvm/MC/MCObjectFileInfo.h

protected:
   MCSection *TOCBaseSection = nullptr;
   MCSection *ReadOnly8Section = nullptr;
   MCSection *ReadOnly16Section = nullptr;
 
   // Swift5 Reflection Data Sections
   std::array<MCSection *, binaryformat::Swift5ReflectionSectionKind::last>
       Swift5ReflectionSections = {};
 
+  unsigned TextSectionAlignment = 4;
+
 public:
   void initMCObjectFileInfo(MCContext &MCCtx, bool PIC,
                             bool LargeCodeModel = false);
   virtual ~MCObjectFileInfo();
   MCContext &getContext() const { return *Ctx; }
 
   bool getSupportsWeakOmittedEHFrame() const {
     return SupportsWeakOmittedEHFrame;
public:
   }
 
   unsigned getFDEEncoding() const { return FDECFIEncoding; }
 
   unsigned getCompactUnwindDwarfEHFrameOnly() const {
     return CompactUnwindDwarfEHFrameOnly;
   }
 
-  virtual unsigned getTextSectionAlignment() const { return 4; }
+  void setTextSectionAlignment(unsigned Alignment) {
+    TextSectionAlignment = Alignment;
+  }
+
+  unsigned getTextSectionAlignment() const { return TextSectionAlignment; }
   MCSection *getTextSection() const { return TextSection; }
   MCSection *getDataSection() const { return DataSection; }
   MCSection *getBSSSection() const { return BSSSection; }
   MCSection *getReadOnlySection() const { return ReadOnlySection; }
   MCSection *getLSDASection() const { return LSDASection; }
   MCSection *getCompactUnwindSection() const { return CompactUnwindSection; }
   MCSection *getDwarfAbbrevSection() const { return DwarfAbbrevSection; }
   MCSection *getDwarfInfoSection() const { return DwarfInfoSection; }

llvm/lib/Target/RISCV/MCTargetDesc/CMakeLists.txt

 add_llvm_component_library(LLVMRISCVDesc
   RISCVAsmBackend.cpp
   RISCVBaseInfo.cpp
   RISCVELFObjectWriter.cpp
   RISCVInstPrinter.cpp
   RISCVMCAsmInfo.cpp
   RISCVMCCodeEmitter.cpp
   RISCVMCExpr.cpp
-  RISCVMCObjectFileInfo.cpp
   RISCVMCTargetDesc.cpp
   RISCVMatInt.cpp
   RISCVTargetStreamer.cpp
   RISCVELFStreamer.cpp
 
   LINK_COMPONENTS
   MC
   RISCVInfo
   Support
 
   ADD_TO_COMPONENT
   RISCV
 )

llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCObjectFileInfo.h

-//===-- RISCVMCObjectFileInfo.h - RISCV object file Info -------*- 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 contains the declaration of the RISCVMCObjectFileInfo class.
-//
-//===----------------------------------------------------------------------===//
-
-#ifndef LLVM_LIB_TARGET_RISCV_MCTARGETDESC_RISCVMCOBJECTFILEINFO_H
-#define LLVM_LIB_TARGET_RISCV_MCTARGETDESC_RISCVMCOBJECTFILEINFO_H
-
-#include "llvm/MC/MCObjectFileInfo.h"
-
-namespace llvm {
-
-class RISCVMCObjectFileInfo : public MCObjectFileInfo {
-public:
-  unsigned getTextSectionAlignment() const override;
-};
-
-} // namespace llvm
-
-#endif

llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCObjectFileInfo.cpp

-//===-- RISCVMCObjectFileInfo.cpp - RISCV object file properties ----------===//
-//
-// 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 contains the declarations of the RISCVMCObjectFileInfo properties.
-//
-//===----------------------------------------------------------------------===//
-
-#include "RISCVMCObjectFileInfo.h"
-#include "RISCVMCTargetDesc.h"
-#include "llvm/MC/MCContext.h"
-#include "llvm/MC/MCSubtargetInfo.h"
-
-using namespace llvm;
-
-unsigned RISCVMCObjectFileInfo::getTextSectionAlignment() const {
-  const MCSubtargetInfo *STI = getContext().getSubtargetInfo();
-  return STI->hasFeature(RISCV::FeatureStdExtC) ? 2 : 4;
-}

llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCTargetDesc.cpp

 ///
 //===----------------------------------------------------------------------===//
 
 #include "RISCVMCTargetDesc.h"
 #include "RISCVBaseInfo.h"
 #include "RISCVELFStreamer.h"
 #include "RISCVInstPrinter.h"
 #include "RISCVMCAsmInfo.h"
-#include "RISCVMCObjectFileInfo.h"
 #include "RISCVTargetStreamer.h"
 #include "TargetInfo/RISCVTargetInfo.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/MC/MCAsmBackend.h"
 #include "llvm/MC/MCAsmInfo.h"
 #include "llvm/MC/MCCodeEmitter.h"
+#include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCInstrAnalysis.h"
 #include "llvm/MC/MCInstrInfo.h"
 #include "llvm/MC/MCObjectFileInfo.h"
 #include "llvm/MC/MCObjectWriter.h"
 #include "llvm/MC/MCRegisterInfo.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MCSubtargetInfo.h"
 #include "llvm/MC/TargetRegistry.h"
static MCAsmInfo *createRISCVMCAsmInfo(const MCRegisterInfo &MRI,
   MAI->addInitialFrameState(Inst);
 
   return MAI;
 }
 
 static MCObjectFileInfo *
 createRISCVMCObjectFileInfo(MCContext &Ctx, bool PIC,
                             bool LargeCodeModel = false) {
-  MCObjectFileInfo *MOFI = new RISCVMCObjectFileInfo();
+  MCObjectFileInfo *MOFI = new MCObjectFileInfo();
   MOFI->initMCObjectFileInfo(Ctx, PIC, LargeCodeModel);
+  const MCSubtargetInfo *STI = MOFI->getContext().getSubtargetInfo();
+  MOFI->setTextSectionAlignment(STI->hasFeature(RISCV::FeatureStdExtC) ? 2 : 4);
   return MOFI;
 }
 
 static MCSubtargetInfo *createRISCVMCSubtargetInfo(const Triple &TT,
                                                    StringRef CPU, StringRef FS) {
   if (CPU.empty() || CPU == "generic")
     CPU = TT.isArch64Bit() ? "generic-rv64" : "generic-rv32";
 

llvm/lib/Target/RISCV/RISCVSubtarget.cpp

 #include "RISCV.h"
 #include "RISCVCallLowering.h"
 #include "RISCVFrameLowering.h"
 #include "RISCVLegalizerInfo.h"
 #include "RISCVRegisterBankInfo.h"
 #include "RISCVTargetMachine.h"
 #include "llvm/MC/TargetRegistry.h"
 #include "llvm/Support/ErrorHandling.h"
+#include "llvm/Target/TargetLoweringObjectFile.h"
 
 using namespace llvm;
 
 #define DEBUG_TYPE "riscv-subtarget"
 
 #define GET_SUBTARGETINFO_TARGET_DESC
 #define GET_SUBTARGETINFO_CTOR
 #include "RISCVGenSubtargetInfo.inc"

llvm/lib/Target/RISCV/RISCVTargetObjectFile.h

 //===-- RISCVTargetObjectFile.h - RISCV Object Info -*- 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
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_LIB_TARGET_RISCV_RISCVTARGETOBJECTFILE_H
 #define LLVM_LIB_TARGET_RISCV_RISCVTARGETOBJECTFILE_H
 
 #include "llvm/CodeGen/TargetLoweringObjectFileImpl.h"
+#include "llvm/MC/MCObjectFileInfo.h"
 
 namespace llvm {
 
 /// This implementation is used for RISCV ELF targets.
 class RISCVELFTargetObjectFile : public TargetLoweringObjectFileELF {
   MCSection *SmallDataSection;
   MCSection *SmallBSSSection;
   unsigned SSThreshold = 8;

llvm/lib/Target/RISCV/RISCVTargetObjectFile.cpp

 void RISCVELFTargetObjectFile::Initialize(MCContext &Ctx,
                                           const TargetMachine &TM) {
   TargetLoweringObjectFileELF::Initialize(Ctx, TM);
 
   SmallDataSection = getContext().getELFSection(
       ".sdata", ELF::SHT_PROGBITS, ELF::SHF_WRITE | ELF::SHF_ALLOC);
   SmallBSSSection = getContext().getELFSection(".sbss", ELF::SHT_NOBITS,
                                                ELF::SHF_WRITE | ELF::SHF_ALLOC);
+  setTextSectionAlignment(
+      Ctx.getSubtargetInfo()->hasFeature(RISCV::FeatureStdExtC) ? 2 : 4);
 }
 
 // A address must be loaded from a small section if its size is less than the
 // small section size threshold. Data in this section could be addressed by
 // using gp_rel operator.
 bool RISCVELFTargetObjectFile::isInSmallSection(uint64_t Size) const {
   // gcc has traditionally not treated zero-sized objects as small data, so this
   // is effectively part of the ABI.

llvm/test/MC/RISCV/unnecessary-code-align.ll

 ; RUN: llc -mtriple=riscv64 -filetype=obj -mattr=+c,+relax %s -o - \
 ; RUN:     | llvm-readobj -r - | FileCheck %s
 
 ; CHECK: Relocations [
-; CHECK:   Section (3) .rela.text {
-; CHECK:     0x0 R_RISCV_ALIGN - 0x2
-; CHECK:   }
+; CHECK-NOT:   Section (3) .rela.text {
+; CHECK-NOT:     0x0 R_RISCV_ALIGN - 0x2
+; CHECK-NOT:   }
 ; CHECK: ]
 define i32 @test() #0 {
 entry:
   ret i32 1
 }
 
 attributes #0 = { nounwind }