[RISCV] RISCVELFTargetObjectFile: use 2-byte alignment for .text if RVC

[MaskRay]

Summary

For the "C" Standard Extension/Zca, D45560 enabled 2-byte alignment for
assembly output (e.g. clang -S a.c) and D102052 enabled 2-byte alignment for
assembly input and object file output (e.g. clang -c a.s).

This patch ports the behavior for code generation and object file output by
adding RISCVELFTargetObjectFile::getTextSectionAlignment (e.g. clang -c a.c).

[craig.topper]

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

15

Isn't this a layering violation?

[MaskRay]

Fix layer violation

[craig.topper]

LGTM

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

 //===-- RISCVMCObjectFileInfo.h - RISC-V 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"
+#include "llvm/MC/MCSubtargetInfo.h"
 
 namespace llvm {
 
 class RISCVMCObjectFileInfo : public MCObjectFileInfo {
 public:
+  static unsigned getTextSectionAlignment(const MCSubtargetInfo &STI);
   unsigned getTextSectionAlignment() const override;
 };
 
 } // namespace llvm
 
 #endif

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

 //===-- RISCVMCObjectFileInfo.cpp - RISC-V 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 MCSubtargetInfo &STI) {
+  bool RVC = STI.hasFeature(RISCV::FeatureStdExtC) ||
+             STI.hasFeature(RISCV::FeatureStdExtZca);
+  return RVC ? 2 : 4;
+}
+
 unsigned RISCVMCObjectFileInfo::getTextSectionAlignment() const {
-  const MCSubtargetInfo *STI = getContext().getSubtargetInfo();
-  return (STI->hasFeature(RISCV::FeatureStdExtC) ||
-          STI->hasFeature(RISCV::FeatureStdExtZca))
-             ? 2
-             : 4;
+  return getTextSectionAlignment(*getContext().getSubtargetInfo());
 }

llvm/lib/Target/RISCV/RISCVTargetObjectFile.h

 
 /// This implementation is used for RISC-V ELF targets.
 class RISCVELFTargetObjectFile : public TargetLoweringObjectFileELF {
   MCSection *SmallDataSection;
   MCSection *SmallBSSSection;
   unsigned SSThreshold = 8;
 
 public:
+  unsigned getTextSectionAlignment() const override;
+
   void Initialize(MCContext &Ctx, const TargetMachine &TM) override;
 
   /// Return true if this global address should be placed into small data/bss
   /// section.
   bool isGlobalInSmallSection(const GlobalObject *GO,
                               const TargetMachine &TM) const;
 
   MCSection *SelectSectionForGlobal(const GlobalObject *GO, SectionKind Kind,

llvm/lib/Target/RISCV/RISCVTargetObjectFile.cpp

 //===-- RISCVTargetObjectFile.cpp - RISC-V Object Info --------------------===//
 //
 // 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 "RISCVTargetObjectFile.h"
+#include "MCTargetDesc/RISCVMCObjectFileInfo.h"
 #include "RISCVTargetMachine.h"
 #include "llvm/BinaryFormat/ELF.h"
 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCSectionELF.h"
 
 using namespace llvm;
 
+unsigned RISCVELFTargetObjectFile::getTextSectionAlignment() const {
+  return RISCVMCObjectFileInfo::getTextSectionAlignment(
+      *getContext().getSubtargetInfo());
+}
+
 void RISCVELFTargetObjectFile::Initialize(MCContext &Ctx,
                                           const TargetMachine &TM) {
   TargetLoweringObjectFileELF::Initialize(Ctx, TM);
 
   PLTRelativeVariantKind = MCSymbolRefExpr::VK_PLT;
 
   SmallDataSection = getContext().getELFSection(
       ".sdata", ELF::SHT_PROGBITS, ELF::SHF_WRITE | ELF::SHF_ALLOC);

llvm/test/CodeGen/RISCV/align.ll

 ; RUN: llc -mtriple=riscv32 -verify-machineinstrs < %s \
 ; RUN:   | FileCheck %s -check-prefix=RV32I
 ; RUN: llc -mtriple=riscv32 -mattr=+c -verify-machineinstrs < %s \
 ; RUN:   | FileCheck %s -check-prefix=RV32C
+; RUN: llc -filetype=obj -mtriple=riscv32 < %s -o %t
+; RUN: llvm-readelf -S %t | FileCheck %s --check-prefixes=SEC,SEC-I
+; RUN: llc -filetype=obj -mtriple=riscv32 -mattr=+c < %s -o %t
+; RUN: llvm-readelf -S %t | FileCheck %s --check-prefixes=SEC,SEC-C
+
+; SEC:   Name   Type     Address  Off      Size     ES Flg Lk Inf Al
+; SEC-I: .text  PROGBITS 00000000 [[#%x,]] [[#%x,]] 00  AX  0   0  4
+; SEC-C: .text  PROGBITS 00000000 [[#%x,]] [[#%x,]] 00  AX  0   0  2
 
 define void @foo() {
 ;RV32I: .p2align 2
 ;RV32I: foo:
 ;RV32C: .p2align 1
 ;RV32C: foo:
 entry:
   ret void
 }