Re: Migration of Cross Compiler from gcc 3.4.6 to gcc 4.1.1

[Ian Lance Taylor <iant at google dot com>]

"Rohit Arul Raj" <rohitarulraj@gmail.com> writes:

> I am upgrading my cross-compiler from 3.4.6 to 4.1.1. It has built
> successfully. But while running the test suites, i am getting lots of
> run time errors during optimization tests (Mostly size optimization -
> Os). But the same code with same level of optimization works fine with
> 3.4.6.
> 
> 1. What are the differences in implementation of optimization levels
> of 3.4.6 and 4.1.1?

The 4.1.1 optimizers are very different from the 3.4.6 optimizers.
4.1.1 uses the tree-ssa framework which was introduced in 4.0.

> 2. For 4.1.1, The same test code works with all levels of optimization
> except -Os.
>    Other than flags, what are the ways in which the implementation of
> Optimization levels differ?

-Os is like -O2 except that it sets the global variable optimize_size.
Grep for optimize_size to see the differences.

Ian