[cfe-dev] RFC: Clang driver redesign (round 2)

[Christopher Jefferson]

On 8 Nov 2011, at 21:48, Chris Lattner wrote:

> On Nov 8, 2011, at 3:23 AM, James Molloy wrote:
>> Thanks for all the replies. I've kind of summarised the main points of
>> contest so far below and tried to group supporters and opponents. If
>> I've grouped you incorrectly, please don't take it slanderously :)
> 
> Just MHO:
> 
>> "To GCC or not to GCC, that is the question"
>> ============================================
>> 
>> +Doug Gregor, Miles Bader
>> -Sean Hunt, Christopher Jefferson, Andrew Trick
>> 
>> There is differing opinion on the amount of GCC compatability clang
>> should offer. A lot of examples and arguments have been given, but I
>> see one conclusion - the driver should not be pinned to anything.
> 
> This is an absolute must-have.  I guess I'm not opposed to having a *second* driver that is "nicer" somehow than the existing one, but we cannot give up GCC compatibility in the main clang driver.
> 
> However, the challenge then becomes "why would anyone use the 'nice' one"?

Ease of use.

I see stories like this over and over again when teaching students.

$ cat test.cc
#include <iostream>

int main(void)
{ 
  int i;
  std::cout << i;
}
$ clang test.cc
Undefined symbols for architecture x86_64:
  "std::ios_base::Init::Init()", referenced from:
      ___cxx_global_var_init in t-vtk1TB.o
  "std::ios_base::Init::~Init()", referenced from:
      ___cxx_global_var_init in t-vtk1TB.o
  "std::cout", referenced from:
      _main in t-vtk1TB.o
  "std::ostream::operator<<(int)", referenced from:
      _main in t-vtk1TB.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
< wander off and ask someone why the code isn't compiling >
$ clang++ test.cc
$ ./a.out
1872097369
< wander off to ask why the code isn't working. Get told to enable warnings >
$ clang++ test.cc -Wall
t.cc:6:16: warning: variable 'i' is uninitialized when used here
      [-Wuninitialized]
  std::cout << i;
               ^
t.cc:5:8: note: initialize the variable 'i' to silence this warning
  int i;
       ^
        = 0
1 warning generated.
< grumbles, add the initialisation, code works>

I think it would be worth trying to reduce the pain here, for a beginner programmer. I'll admit I don't know the best way of doing that.


Chris