[llvm] Fix D26214: Move error handling out of MC and to the callers.

[mgrang]

Summary

Related clang patch; https://reviews.llvm.org/D27360

[compnerd]

This is definitely an improvement. Printing out to errs from MC is less than ideal, especially given all the work that has gone in to pipe messages back from the MCAssembler.

[echristo]

This is better, yes.

include/llvm/MC/MCContext.h

public:
     MCSymbol *getOrCreateParentFrameOffsetSymbol(StringRef FuncName);
 
     MCSymbol *getOrCreateLSDASymbol(StringRef FuncName);
 
     /// Get the symbol for \p Name, or null.
     MCSymbol *lookupSymbol(const Twine &Name) const;
 
     /// Set value for a symbol.
-    int setSymbolValue(MCStreamer &Streamer, std::string &I);
+    void setSymbolValue(MCStreamer &Streamer, StringRef Sym, uint64_t Val);
 
     /// getSymbols - Get a reference for the symbol table for clients that
     /// want to, for example, iterate over all symbols. 'const' because we
     /// still want any modifications to the table itself to use the MCContext
     /// APIs.
     const SymbolTable &getSymbols() const { return Symbols; }
 
     /// @}

lib/MC/MCContext.cpp

 }
 
 MCSymbol *MCContext::lookupSymbol(const Twine &Name) const {
   SmallString<128> NameSV;
   StringRef NameRef = Name.toStringRef(NameSV);
   return Symbols.lookup(NameRef);
 }
 
-int MCContext::setSymbolValue(MCStreamer &Streamer, std::string &I) {
-    auto Pair = StringRef(I).split('=');
-    if (Pair.second.empty()) {
-      errs() << "error: defsym must be of the form: sym=value: " << I << "\n";
-      return 1;
-    }
-    int64_t Value;
-    if (Pair.second.getAsInteger(0, Value)) {
-      errs() << "error: Value is not an integer: " << Pair.second << "\n";
-      return 1;
-    }
-    auto Symbol = getOrCreateSymbol(Pair.first);
-    Streamer.EmitAssignment(Symbol, MCConstantExpr::create(Value, *this));
-    return 0;
+void MCContext::setSymbolValue(MCStreamer &Streamer,
+                              StringRef Sym,
+                              uint64_t Val) {
+  auto Symbol = getOrCreateSymbol(Sym);
+  Streamer.EmitAssignment(Symbol, MCConstantExpr::create(Val, *this));
 }
 
 //===----------------------------------------------------------------------===//
 // Section Management
 //===----------------------------------------------------------------------===//
 
 MCSectionMachO *MCContext::getMachOSection(StringRef Segment, StringRef Section,
                                            unsigned TypeAndAttributes,

tools/llvm-mc/llvm-mc.cpp

while (Lexer.Lex().isNot(AsmToken::Eof)) {
     OS.write_escaped(Tok.getString());
     OS << "\")\n";
   }
 
   return Error;
 }
 
 static int fillCommandLineSymbols(MCAsmParser &Parser) {
-  for (auto &I: DefineSymbol)
-    if (Parser.getContext().setSymbolValue(Parser.getStreamer(), I))
+  for (auto &I: DefineSymbol) {
+    auto Pair = StringRef(I).split('=');
+    auto Sym = Pair.first;
+    auto Val = Pair.second;
+
+    if (Sym.empty() || Val.empty()) {
+      errs() << "error: defsym must be of the form: sym=value: " << I << "\n";
+      return 1;
+    }
+    int64_t Value;
+    if (Val.getAsInteger(0, Value)) {
+      errs() << "error: Value is not an integer: " << Val << "\n";
       return 1;
+    }
+    Parser.getContext().setSymbolValue(Parser.getStreamer(), Sym, Value);
+  }
   return 0;
 }
 
 static int AssembleInput(const char *ProgName, const Target *TheTarget,
                          SourceMgr &SrcMgr, MCContext &Ctx, MCStreamer &Str,
                          MCAsmInfo &MAI, MCSubtargetInfo &STI,
                          MCInstrInfo &MCII, MCTargetOptions &MCOptions) {
   std::unique_ptr<MCAsmParser> Parser(