[Object][NFC] Remove unneeded llvm_unreachable

[gAlfonso-bit]

Summary

The structure of this method now matches the one above it.

[MaskRay]

I agree that the call site uses are somewhat problematic, but cast has stronger guarantee. Do you have a test case to trigger a code path that dyn_cast returns nullptr? If not, the if statement should just be replaced with unconditional cast.

llvm/lib/Object/ELFObjectFile.cpp

803

This can just used cast and delete llvm_unreachable

[gAlfonso-bit]

This comment was removed by gAlfonso-bit.

[MaskRay]

llvm/utils/TableGen/DecoderEmitter.cpp

2111

See the reverted ba59ec2843f99f19d55d7cd9f9ac536fb038fdab: this change seems wrong.

[gAlfonso-bit]

This comment was removed by gAlfonso-bit.

[craig.topper]

llvm/lib/MC/MCExpr.cpp

887–888

R isn't checked for null after this so if the dynamic cast fails it will dereference a null point. cast would have generated an assert on assertion builds.

[gAlfonso-bit]

This comment was removed by gAlfonso-bit.

[gAlfonso-bit]

This comment was removed by gAlfonso-bit.

[MaskRay]

In D139452#4132950, @gAlfonso-bit wrote:

@MaskRay Can I have commit permissions please

I'll land this patch for you. Your previous changes are all about this kind of NFC cleanup. I think I only want to endorse people with contributions like bug fixing or useful feature requests...

llvm/lib/MC/MCExpr.cpp

bool MCExpr::evaluateAsRelocatableImpl(MCValue &Res, const MCAssembler *Asm,
   case Binary: {
     const MCBinaryExpr *ABE = cast<MCBinaryExpr>(this);
     MCValue LHSValue, RHSValue;
 
     if (!ABE->getLHS()->evaluateAsRelocatableImpl(LHSValue, Asm, Layout, Fixup,
                                                   Addrs, InSet) ||
         !ABE->getRHS()->evaluateAsRelocatableImpl(RHSValue, Asm, Layout, Fixup,
                                                   Addrs, InSet)) {
       // Check if both are Target Expressions, see if we can compare them.
       if (const MCTargetExpr *L = dyn_cast<MCTargetExpr>(ABE->getLHS()))
-        if (const MCTargetExpr *R = cast<MCTargetExpr>(ABE->getRHS())) {
+        if (const MCTargetExpr *R = dyn_cast<MCTargetExpr>(ABE->getRHS())) {
           switch (ABE->getOpcode()) {
           case MCBinaryExpr::EQ:
             Res = MCValue::get((L->isEqualTo(R)) ? -1 : 0);
             return true;
           case MCBinaryExpr::NE:
             Res = MCValue::get((R->isEqualTo(R)) ? 0 : -1);
             return true;
           default: break;

llvm/lib/Object/ELFObjectFile.cpp

 Expected<std::vector<BBAddrMap>> ELFObjectFileBase::readBBAddrMap(
     std::optional<unsigned> TextSectionIndex) const {
   if (const auto *Obj = dyn_cast<ELF32LEObjectFile>(this))
     return readBBAddrMapImpl(Obj->getELFFile(), TextSectionIndex);
   if (const auto *Obj = dyn_cast<ELF64LEObjectFile>(this))
     return readBBAddrMapImpl(Obj->getELFFile(), TextSectionIndex);
   if (const auto *Obj = dyn_cast<ELF32BEObjectFile>(this))
     return readBBAddrMapImpl(Obj->getELFFile(), TextSectionIndex);
-  if (const auto *Obj = cast<ELF64BEObjectFile>(this))
+  if (const auto *Obj = dyn_cast<ELF64BEObjectFile>(this))
     return readBBAddrMapImpl(Obj->getELFFile(), TextSectionIndex);
   else
     llvm_unreachable("Unsupported binary format");
 }

llvm/utils/TableGen/DecoderEmitter.cpp

if (SupportPositionalDecoding) {
             DecoderString ? dyn_cast<StringInit>(DecoderString->getValue())
                           : nullptr;
         if (String && String->getValue() != "")
           Decoder = std::string(String->getValue());
 
         if (Decoder == "" && CGI.Operands[SO.first].MIOperandInfo &&
             CGI.Operands[SO.first].MIOperandInfo->getNumArgs()) {
           Init *Arg = CGI.Operands[SO.first].MIOperandInfo->getArg(SO.second);
-          if (DefInit *DI = cast<DefInit>(Arg))
+          if (DefInit *DI = dyn_cast<DefInit>(Arg))
             TypeRecord = DI->getDef();
         }
 
         bool isReg = false;
         if (TypeRecord->isSubClassOf("RegisterOperand"))
           TypeRecord = TypeRecord->getValueAsDef("RegClass");
         if (TypeRecord->isSubClassOf("RegisterClass")) {
           Decoder = "Decode" + TypeRecord->getName().str() + "RegisterClass";