[lld] Use StringRef idioms (NFC) (llvm#109584)

Author: kazutakahirata

lld/COFF/Driver.cpp

@@ -113,9 +113,8 @@ static std::string getOutputPath(StringRef path, bool isDll, bool isDriver) {
 
 // Returns true if S matches /crtend.?\.o$/.
 static bool isCrtend(StringRef s) {
-  if (!s.ends_with(".o"))
+  if (!s.consume_back(".o"))
     return false;
-  s = s.drop_back(2);
   if (s.ends_with("crtend"))
     return true;
   return !s.empty() && s.drop_back().ends_with("crtend");

lld/Common/DriverDispatcher.cpp

@@ -113,8 +113,7 @@ parseFlavorWithoutMinGW(llvm::SmallVectorImpl<const char *> &argsV) {
 
   // Deduct the flavor from argv[0].
   StringRef arg0 = path::filename(argsV[0]);
-  if (arg0.ends_with_insensitive(".exe"))
-    arg0 = arg0.drop_back(4);
+  arg0.consume_back_insensitive(".exe");
   Flavor f = parseProgname(arg0);
   if (f == Invalid) {
     err("lld is a generic driver.\n"

lld/ELF/Driver.cpp

@@ -866,8 +866,7 @@ static StripPolicy getStrip(opt::InputArgList &args) {
 static uint64_t parseSectionAddress(StringRef s, opt::InputArgList &args,
                                     const opt::Arg &arg) {
   uint64_t va = 0;
-  if (s.starts_with("0x"))
-    s = s.drop_front(2);
+  s.consume_front("0x");
   if (!to_integer(s, va, 16))
     error("invalid argument: " + arg.getAsString(args));
   return va;

lld/MachO/InputSection.cpp

@@ -167,8 +167,7 @@ std::string InputSection::getSourceLocation(uint64_t off) const {
     // Symbols are generally prefixed with an underscore, which is not included
     // in the debug information.
     StringRef symName = sym->getName();
-    if (!symName.empty() && symName[0] == '_')
-      symName = symName.substr(1);
+    symName.consume_front("_");
 
     if (std::optional<std::pair<std::string, unsigned>> fileLine =
             dwarf->getVariableLoc(symName))