Simplified WebAssemblyAsmBackend by removing explicit ELF variant.

[aardappel]

Summary

The ELF version was broken (does not deal with wasm specific fixups),
and now is slightly less broken. It will be removed in its entirety
in the future which this change makes slightly easier (just remove
the IsELF bool).

[sbc100]

lib/Target/WebAssembly/MCTargetDesc/WebAssemblyAsmBackend.cpp

125 ↗

(On Diff #149860)

IIRC we could probably abort here in the elf case as I think ELF is only used to produce .s format files, not object files.

I guess that might be a separate/larger change so this LGTM as is keep the change small.

[dschuff]

LGTM, we can remove any code relating to binary output with the ELF triple now. Hopefully not much longer before we can remove the ELF triple entirely.

[dschuff]

lib/Target/WebAssembly/MCTargetDesc/WebAssemblyAsmBackend.cpp

125 ↗

(On Diff #149860)

Yeah we should be able to remove the ELF object writer too.

[aardappel]

lib/Target/WebAssembly/MCTargetDesc/WebAssemblyAsmBackend.cpp

125 ↗

(On Diff #149860)

Yes, I was going to fix ELF behavior until Derek pointed out the uselessness of that. So this commit just simplifies code.

llvm/trunk/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyAsmBackend.cpp

 #include "llvm/MC/MCSubtargetInfo.h"
 #include "llvm/MC/MCSymbol.h"
 #include "llvm/MC/MCWasmObjectWriter.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/raw_ostream.h"
 using namespace llvm;
 
 namespace {
-class WebAssemblyAsmBackendELF final : public MCAsmBackend {
-  bool Is64Bit;
-
-public:
-  explicit WebAssemblyAsmBackendELF(bool Is64Bit)
-      : MCAsmBackend(support::little), Is64Bit(Is64Bit) {}
-  ~WebAssemblyAsmBackendELF() override {}
-
-  void applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
-                  const MCValue &Target, MutableArrayRef<char> Data,
-                  uint64_t Value, bool IsPCRel) const override;
-
-  std::unique_ptr<MCObjectTargetWriter>
-  createObjectTargetWriter() const override;
-
-  // No instruction requires relaxation
-  bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,
-                            const MCRelaxableFragment *DF,
-                            const MCAsmLayout &Layout) const override {
-    return false;
-  }
-
-  unsigned getNumFixupKinds() const override {
-    // We currently just use the generic fixups in MCFixup.h and don't have any
-    // target-specific fixups.
-    return 0;
-  }
-
-  bool mayNeedRelaxation(const MCInst &Inst) const override { return false; }
-
-  void relaxInstruction(const MCInst &Inst, const MCSubtargetInfo &STI,
-                        MCInst &Res) const override {}
-
-  bool writeNopData(raw_ostream &OS, uint64_t Count) const override;
-};
 
 class WebAssemblyAsmBackend final : public MCAsmBackend {
   bool Is64Bit;
+  bool IsELF;
 
  public:
-  explicit WebAssemblyAsmBackend(bool Is64Bit)
-      : MCAsmBackend(support::little), Is64Bit(Is64Bit) {}
+  explicit WebAssemblyAsmBackend(bool Is64Bit, bool IsELF)
+      : MCAsmBackend(support::little), Is64Bit(Is64Bit), IsELF(IsELF) {}
   ~WebAssemblyAsmBackend() override {}
 
   unsigned getNumFixupKinds() const override {
     return WebAssembly::NumTargetFixupKinds;
   }
 
   const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const override;
 
public:
   bool mayNeedRelaxation(const MCInst &Inst) const override { return false; }
 
   void relaxInstruction(const MCInst &Inst, const MCSubtargetInfo &STI,
                         MCInst &Res) const override {}
 
   bool writeNopData(raw_ostream &OS, uint64_t Count) const override;
 };
 
-bool WebAssemblyAsmBackendELF::writeNopData(raw_ostream &OS,
-                                            uint64_t Count) const {
-  for (uint64_t i = 0; i < Count; ++i)
-    OS << char(WebAssembly::Nop);
-
-  return true;
-}
-
-void WebAssemblyAsmBackendELF::applyFixup(const MCAssembler &Asm,
-                                          const MCFixup &Fixup,
-                                          const MCValue &Target,
-                                          MutableArrayRef<char> Data,
-                                          uint64_t Value, bool IsPCRel) const {
-  const MCFixupKindInfo &Info = getFixupKindInfo(Fixup.getKind());
-  assert(Info.Flags == 0 && "WebAssembly does not use MCFixupKindInfo flags");
-
-  unsigned NumBytes = alignTo(Info.TargetSize, 8) / 8;
-  if (Value == 0)
-    return; // Doesn't change encoding.
-
-  // Shift the value into position.
-  Value <<= Info.TargetOffset;
-
-  unsigned Offset = Fixup.getOffset();
-  assert(Offset + NumBytes <= Data.size() && "Invalid fixup offset!");
-
-  // For each byte of the fragment that the fixup touches, mask in the
-  // bits from the fixup value.
-  for (unsigned i = 0; i != NumBytes; ++i)
-    Data[Offset + i] |= uint8_t((Value >> (i * 8)) & 0xff);
-}
-
-std::unique_ptr<MCObjectTargetWriter>
-WebAssemblyAsmBackendELF::createObjectTargetWriter() const {
-  return createWebAssemblyELFObjectWriter(Is64Bit, 0);
-}
-
 const MCFixupKindInfo &
 WebAssemblyAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
   const static MCFixupKindInfo Infos[WebAssembly::NumTargetFixupKinds] = {
     // This table *must* be in the order that the fixup_* kinds are defined in
     // WebAssemblyFixupKinds.h.
     //
     // Name                     Offset (bits) Size (bits)     Flags
     { "fixup_code_sleb128_i32", 0,            5*8,            0 },
     { "fixup_code_sleb128_i64", 0,            10*8,           0 },
     { "fixup_code_uleb128_i32", 0,            5*8,            0 },
   };
 
   if (Kind < FirstTargetFixupKind)
     return MCAsmBackend::getFixupKindInfo(Kind);
 
   assert(unsigned(Kind - FirstTargetFixupKind) < getNumFixupKinds() &&
          "Invalid kind!");
   return Infos[Kind - FirstTargetFixupKind];
 }
 
 bool WebAssemblyAsmBackend::writeNopData(raw_ostream &OS,
                                          uint64_t Count) const {
-  if (Count == 0)
-    return true;
-
   for (uint64_t i = 0; i < Count; ++i)
     OS << char(WebAssembly::Nop);
 
   return true;
 }
 
 void WebAssemblyAsmBackend::applyFixup(const MCAssembler &Asm,
                                        const MCFixup &Fixup,
void WebAssemblyAsmBackend::applyFixup(const MCAssembler &Asm,
   // For each byte of the fragment that the fixup touches, mask in the
   // bits from the fixup value.
   for (unsigned i = 0; i != NumBytes; ++i)
     Data[Offset + i] |= uint8_t((Value >> (i * 8)) & 0xff);
 }
 
 std::unique_ptr<MCObjectTargetWriter>
 WebAssemblyAsmBackend::createObjectTargetWriter() const {
-  return createWebAssemblyWasmObjectWriter(Is64Bit);
+  return IsELF ? createWebAssemblyELFObjectWriter(Is64Bit, 0)
+               : createWebAssemblyWasmObjectWriter(Is64Bit);
 }
+
 } // end anonymous namespace
 
 MCAsmBackend *llvm::createWebAssemblyAsmBackend(const Triple &TT) {
-  if (TT.isOSBinFormatELF())
-    return new WebAssemblyAsmBackendELF(TT.isArch64Bit());
-  return new WebAssemblyAsmBackend(TT.isArch64Bit());
+  return new WebAssemblyAsmBackend(TT.isArch64Bit(), TT.isOSBinFormatELF());
 }