[tree-ssa]: Dump file option names and small DCE fix

[Diego Novillo]

On Wed, 18 Sep 2002, Daniel Berlin wrote:

> In trying out DCE, I noticed that it fcloses the dump_file in the same 
> if block it opens it in, so nothing besides a pre-dce dump gets printed 
> to it.
> 
Thanks.  This is OK.


> I fixed this, and took the time to canonicalize the dump 
> option/file/enum names as we talked about earlier.
> They now match the -f option. So we have -ftree-ssa-ccp and 
> -fdump-tree-ssa-ccp, and the enum is TDI_ssa_ccp.
> 
You know, I've been thinking about this whole naming convention.
After having typed -fdump-tree-...blah...blah like a million
times, I'm finding these long names really annoying.

Would it break your heart if we removed the ssa prefix from all
these names?  After all, we already know that these passes are
working on SSA, and to the end-user the fact that they are using
SSA or not is irrelevant.  If, at a later date, we implement say
a DCE pass that doesn't use SSA, then we can name it differently.
What I propose is:

-ftree-ssa		=> Goes away.  Indirectly enabled by the
			   other switches.
-ftree-ssa-ccp		=> -ftree-ccp
-ftree-ssa-dce		=> -ftree-dce
-ftree-ssa-pre		=> -ftree-pre

Similarly, we drop 'ssa' from the -fdump-tree switches.


> After doing this, on a simple example, DCE eliminated everything.
> The reason was that it doesn't consider return_stmt's inherently 
> necessary.
> 
Hmm, I think this is wrong.  A return statement shouldn't be
inherently necessary.  Consider:

	if (impossible)
	  return;

By making the return inherently necessary, you trick DCE into
leaving the if() that we already know is impossible.  You may
have found a bug in the DFA information that led DCE to consider
it unnecessary.  Could you post the testcase?


Thanks.  Diego.