我怎么知道代码中的哪些部分从未使用过？

-Wunused

-Wunreachable-code

catch

gcov

-ffunction-sections

-fdata-sections

-Wl,--gc-sections,--print-gc-sections

--print-gc-sections

-fvisibility=hidden

-Wunused

-Wunreachable-code

double x = sqrt(2);
if (x > 5)
{
  doStuff();
}

int y;
cin >> y;
double x = sqrt((double)y);

if (x != 0 && x < 1)
{
  doStuff();
}

sqrt

(double)y

sqrt

sqrt

watch "make 2>&1"

callgrind

valgrind

// <Name>Potentially dead Methods</Name>
warnif count > 0
// Filter procedure for methods that should'nt be considered as dead
let canMethodBeConsideredAsDeadProc = new Func<IMethod, bool>(
    m => !m.IsPublic &&       // Public methods might be used by client applications of your Projects.
         !m.IsEntryPoint &&            // Main() method is not used by-design.
         !m.IsClassConstructor &&      
         !m.IsVirtual &&               // Only check for non virtual method that are not seen as used in IL.
         !(m.IsConstructor &&          // Don't take account of protected ctor that might be call by a derived ctors.
           m.IsProtected) &&
         !m.IsGeneratedByCompiler
)

// Get methods unused
let methodsUnused = 
   from m in JustMyCode.Methods where 
   m.NbMethodsCallingMe == 0 && 
   canMethodBeConsideredAsDeadProc(m)
   select m

// Dead methods = methods used only by unused methods (recursive)
let deadMethodsMetric = methodsUnused.FillIterative(
   methods => // Unique loop, just to let a chance to build the hashset.
              from o in new[] { new object() }
              // Use a hashet to make Intersect calls much faster!
              let hashset = methods.ToHashSet()
              from m in codeBase.Application.Methods.UsedByAny(methods).Except(methods)
              where canMethodBeConsideredAsDeadProc(m) &&
                    // Select methods called only by methods already considered as dead
                    hashset.Intersect(m.MethodsCallingMe).Count() == m.NbMethodsCallingMe
              select m)

from m in JustMyCode.Methods.Intersect(deadMethodsMetric.DefinitionDomain)
select new { m, m.MethodsCallingMe, depth = deadMethodsMetric[m] }

Warn whenever a variable is unused aside from its declaration, whenever a function is declared static but never defined, whenever a label is declared but not used, and whenever a statement computes a result that is explicitly not used.

This option is intended to warn when the compiler detects that at least a whole line of source code will never be executed, because some condition is never satisfied or because it is after a procedure that never returns.