[LLVMdev] std::cout << *MyModule does not work anymore

[Daniel Dunbar]

On Mon, Aug 24, 2009 at 5:40 PM, Óscar Fuentes<ofv at wanadoo.es> wrote:
> It seems that support for dumping text representation of LLVM objects to
> standard channels and C++ output streams was removed. My guess is that
> now we must use errs() instead of std::cerr, llvm::raw_fd_ostream
> instead of std::ofstream, etc.

Correct. std::ostream has been purged from LLVM; the only exception is
the raw_os_ostream class, which can be used to adapt an std::ostream
for use with raw_ostream. This should be enough for clients which want
to keep using std::ostream.

> The changes are not trivial, as for instance llvm::raw_fd_ostream
> without flags fails if the file exists, but std::ofstream does not. The
> changes include using new names for flags that already exist on the
> standard namespace (F_Force instead of O_TRUNC, etc).

I believe that Dan plans to fix the "force by default" issue, at least.

> Is all this an unintended change or an intentional one, and if the
> later, could you direct me to something that explains what we gain on
> exchange of this restriction?

Intentional. std::ostream has long been deprecated in LLVM, each
release has increased the degree of deprecation. The coding standards
document has various bits of information on this
http://llvm.org/docs/CodingStandards.html.

Among other things, you gain performance. raw_ostream is considerably
faster than std::ostream. This is the performance difference on the my
synthetic raw_ostream benchmark:
- raw_fd_ostream (outs()) -
--
name	  avg  	  min  	  med  	  max  	   SD  	 total
user	 1.0002	 0.9990	 0.9992	 1.0024	 0.0015	 3.0006
 sys	 0.0089	 0.0074	 0.0079	 0.0114	 0.0018	 0.0268
wall	 1.0368	 1.0137	 1.0185	 1.0782	 0.0294	 3.1104
--

- std::ostream (cout) -
--
name	  avg  	  min  	  med  	  max  	   SD  	 total
user	 6.8846	 6.8807	 6.8853	 6.8878	 0.0029	20.6537
 sys	 0.0384	 0.0377	 0.0352	 0.0423	 0.0029	 0.1152
wall	 6.9852	 6.9685	 6.9756	 7.0115	 0.0188	20.9555
--

 - Daniel