[patch] Fix tree-optimization/20139.

[Jeffrey A Law]

On Tue, 2005-02-22 at 20:52 -0500, Kazu Hirata wrote:
> Hi,
> 
> Attached is a patch to fix tree-optimization/20139.
> 
> Consider the attached testcase.
> 
> TER changes
> 
>   p_2 = ABS_EXPR <x_1>;
>   if (p_2 < 0.0) goto <L0>; else goto <L1>;
> 
> into
> 
>   if (ABS_EXPR <x> < 0.0) goto <L0>; else goto <L1>;
> 
> which would get folded by fold in find_taken_edge, which I recently
> removed, causing a missed optimization at tree level.
> 
> The patch essentially restores fold for the last run of
> cleanup_tree_cfg by running fold_cond_expr_cond immediately before
> cleanup_tree_cfg.
> 
> IMHO, the right thing to do is to propagate the range of ABS_EXPR's
> result, and fold the "if" statement accordingly.  I hope this patch
> will be reverted in 4.1 once we start doing a good VRP.
> 
> Some people are for removing gcc.c-torture/execute/20020720-1.c as the
> testcase in this patch will be stronger in that it checks that "if" is
> gone at tree level.  Others don't see a reason for removing the old
> testcase.  Personally, I can go with either option.
> 
> Tested on i686-pc-linux-gnu.  OK to apply?
> 
> Kazu Hirata
> 
> 2005-02-22  Kazu Hirata  <kazu@cs.umass.edu>
> 
> 	PR tree-optimization/20139
> 	* tree-cfg.c (fold_cond_expr_cond): Export.
> 	* tree-flow.h: Add a prototype for fold_cond_expr_cond.
> 	* tree-optimize.c (execute_cleanup_cfg_post_optimizing): Call
> 	fold_cond_expr_cond.
> 
> 2005-02-22  Kazu Hirata  <kazu@cs.umass.edu>
> 
> 	PR tree-optimization/20139
> 	* gcc.dg/tree-ssa/pr20139.c: New.
FWIW, we might consider just folding any expression that is subject
to TER.  I've got a patch somewhere around here which does that.  

Mostly it seems to eliminate casts, but from time to time it finds
something it can zap in complex expressions.

Thoughts?
jeff