Quality of GCC 3.1

[Will Cohen]

Wit Jakuczun wrote:
> I have few comments and questions on quality of code generated by g++ 
> from GCC 3.1.
> 
> 1) Compiler seems to be much slower than GCC 2.95.2 (3 times on average).
> 	The code heavily uses STL and exceptions. 

There has been some earlier email pointing out that the compile-times 
have increased. However, this was in reference to C code and 
bootstrapping the compiler rather than C++ code.

> 2) Code generated is much slower (3 times on average) especially if streams
> 	are used

Do you have some concise examples that demonstrate this problem? It is 
hard to fix the problem without test cases. Having a test case that 
allows other people to replicate the problem helps immensely.

> Questions:
> a)	What is the reason of such big decrease in performance especially if
> 	exceptions and/or streams are used?
> b)	Is it a problem of setting correct options for GCC 3.1?
> c)	Where can I find a good comparison of C++ compilers?
> 
> Options I used to make GCC3.1 (using GCC 2.92.2):
> --enable-threads --enable-nls --enable-cstdio=stdio

Did you "make bootstrap"? If you are just using the GCC 3.1 executable 
generated by GCC 2.95.2(?), that may be part of the problem. If you do 
not bootstrap the compiler, you are measuring the performance and 
efficiency of the code generated by gcc 2.95.2 when you measure 
compile-time.

The runtime libraries can also influence the performance. How much time 
is the code spending in the libraries versus in the GCC user code?


-Will