[MC][RISCV] Add RISCV MCObjectFileInfo

This makes sure, that the text section will have a 2-byte alignment, if
the +c extension is enabled.

Reviewed By: MaskRay, luismarques

Differential Revision: https://reviews.llvm.org/D102052

llvm/include/llvm/MC/MCObjectFileInfo.h

@@ -231,6 +231,7 @@ protected:
 public:
   void initMCObjectFileInfo(MCContext &MCCtx, bool PIC,
                             bool LargeCodeModel = false);
+  virtual ~MCObjectFileInfo();
   MCContext &getContext() const { return *Ctx; }
 
   bool getSupportsWeakOmittedEHFrame() const {
@@ -253,6 +254,7 @@ public:
     return CompactUnwindDwarfEHFrameOnly;
   }
 
+  virtual unsigned getTextSectionAlignment() const { return 4; }
   MCSection *getTextSection() const { return TextSection; }
   MCSection *getDataSection() const { return DataSection; }
   MCSection *getBSSSection() const { return BSSSection; }

llvm/lib/MC/MCELFStreamer.cpp

@@ -91,7 +91,7 @@ void MCELFStreamer::mergeFragment(MCDataFragment *DF,
 void MCELFStreamer::InitSections(bool NoExecStack) {
   MCContext &Ctx = getContext();
   SwitchSection(Ctx.getObjectFileInfo()->getTextSection());
-  emitCodeAlignment(4);
+  emitCodeAlignment(Ctx.getObjectFileInfo()->getTextSectionAlignment());
 
   if (NoExecStack)
     SwitchSection(Ctx.getAsmInfo()->getNonexecutableStackSection(Ctx));

llvm/lib/MC/MCObjectFileInfo.cpp

@@ -981,6 +981,8 @@ void MCObjectFileInfo::initXCOFFMCObjectFileInfo(const Triple &T) {
       /* MultiSymbolsAllowed */ true, ".dwmac", XCOFF::SSUBTYP_DWMAC);
 }
 
+MCObjectFileInfo::~MCObjectFileInfo() {}
+
 void MCObjectFileInfo::initMCObjectFileInfo(MCContext &MCCtx, bool PIC,
                                             bool LargeCodeModel) {
   PositionIndependent = PIC;

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

@@ -6,6 +6,7 @@ add_llvm_component_library(LLVMRISCVDesc
   RISCVMCAsmInfo.cpp
   RISCVMCCodeEmitter.cpp
   RISCVMCExpr.cpp
+  RISCVMCObjectFileInfo.cpp
   RISCVMCTargetDesc.cpp
   RISCVMatInt.cpp
   RISCVTargetStreamer.cpp

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

@@ -0,0 +1,22 @@
+//===-- 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"
+
+using namespace llvm;
+
+unsigned RISCVMCObjectFileInfo::getTextSectionAlignment() const {
+  const MCSubtargetInfo *STI = getContext().getSubtargetInfo();
+  return STI->hasFeature(RISCV::FeatureStdExtC) ? 2 : 4;
+}

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

@@ -0,0 +1,27 @@
+//===-- 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/RISCVMCTargetDesc.cpp

@@ -15,6 +15,7 @@
 #include "RISCVELFStreamer.h"
 #include "RISCVInstPrinter.h"
 #include "RISCVMCAsmInfo.h"
+#include "RISCVMCObjectFileInfo.h"
 #include "RISCVTargetStreamer.h"
 #include "TargetInfo/RISCVTargetInfo.h"
 #include "llvm/ADT/STLExtras.h"
@@ -23,6 +24,7 @@
 #include "llvm/MC/MCCodeEmitter.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"
@@ -65,6 +67,14 @@ static MCAsmInfo *createRISCVMCAsmInfo(const MCRegisterInfo &MRI,
   return MAI;
 }
 
+static MCObjectFileInfo *
+createRISCVMCObjectFileInfo(MCContext &Ctx, bool PIC,
+                            bool LargeCodeModel = false) {
+  MCObjectFileInfo *MOFI = new RISCVMCObjectFileInfo();
+  MOFI->initMCObjectFileInfo(Ctx, PIC, LargeCodeModel);
+  return MOFI;
+}
+
 static MCSubtargetInfo *createRISCVMCSubtargetInfo(const Triple &TT,
                                                    StringRef CPU, StringRef FS) {
   if (CPU.empty())
@@ -155,6 +165,7 @@ MCStreamer *createRISCVELFStreamer(const Triple &T, MCContext &Context,
 extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeRISCVTargetMC() {
   for (Target *T : {&getTheRISCV32Target(), &getTheRISCV64Target()}) {
     TargetRegistry::RegisterMCAsmInfo(*T, createRISCVMCAsmInfo);
+    TargetRegistry::RegisterMCObjectFileInfo(*T, createRISCVMCObjectFileInfo);
     TargetRegistry::RegisterMCInstrInfo(*T, createRISCVMCInstrInfo);
     TargetRegistry::RegisterMCRegInfo(*T, createRISCVMCRegisterInfo);
     TargetRegistry::RegisterMCAsmBackend(*T, createRISCVAsmBackend);

llvm/test/MC/RISCV/align.s

@@ -33,13 +33,15 @@
 # Linker could satisfy alignment by removing NOPs after linker relaxation.
 
 # The first R_RISCV_ALIGN come from
-# MCELFStreamer::InitSections() emitCodeAlignment(4).
+# MCELFStreamer::InitSections() emitCodeAlignment(getTextSectionAligntment()).
 # C-EXT-RELAX-RELOC: R_RISCV_ALIGN - 0x2
 # C-EXT-RELAX-INST:  c.nop
 test:
 	.p2align 2
-# C-EXT-RELAX-RELOC: R_RISCV_ALIGN - 0x2
-# C-EXT-RELAX-INST:  c.nop
+# If the +c extension is enabled, the text section will be 2-byte aligned, so
+# one c.nop instruction is sufficient.
+# C-EXT-RELAX-RELOC-NOT: R_RISCV_ALIGN - 0x2
+# C-EXT-RELAX-INST-NOT:  c.nop
 	bne     zero, a0, .LBB0_2
 	mv	a0, zero
 	.p2align 3