Need some clarification about optimization flags, what "exactly" does -O1 do?

[Andrew Haley]

Diego Novillo wrote:
> On Fri, Nov 28, 2008 at 05:58, Andrew Haley <aph@redhat.com> wrote:
> 
>> That's interesting.  tree-dce is Dead Code Elimination on trees, where
>> gcc removes code that can't possibly be reached.
> 
> Strictly speaking, DCE removes code that can't possibly affect the
> output of the program.  Unreachable code is removed by the CFG cleanup
> helper.  Apologies for nitpicking, but this distinction is handled in
> two different spots in the compiler, so it may affect what files/dumps
> you need to look at.

Thanks for the nitpick -- input always appreciated! -- but we already
know this is dce, having discovered that disabling dce fixes the problem,
so the dce dumps are what we need to inspect.  I guess it's possible,
though, that a dce change causes a later pass to do something different.

Andrew.