Re: [PATCH GCC]Improve loop bound info by simplifying conversions in iv base

[Jeff Law <law@redhat.com>]

On 07/28/2015 03:38 AM, Bin Cheng wrote:
> Hi,
> For now, SCEV may compute iv base in the form of "(signed T)((unsigned
> T)base + step))".  This complicates other optimizations/analysis depending
> on SCEV because it's hard to dive into type conversions.  For many cases,
> such type conversions can be simplified with additional range information
> implied by loop initial conditions.  This patch does such simplification.
> With simplified iv base, loop niter analysis can compute more accurate bound
> information since sensible value range can be derived for "base+step".  For
> example, accurate loop bound&may_be_zero information is computed for cases
> added by this patch.
> The code is actually borrowed from loop_exits_before_overflow.  Moreover,
> with simplified iv base, the second case handled in that function now
> becomes the first case.  I didn't remove that part of code because it may(?)
> still be visited in scev analysis itself and simple_iv isn't an interface
> for that.
>
> Is it OK?
>
> Thanks,
> bin
>
> 2015-07-28  Bin Cheng  <bin.cheng@arm.com>
>
> 	* tree-ssa-loop-niter.c (tree_simplify_using_condition): Export
> 	the interface.
> 	* tree-ssa-loop-niter.h (tree_simplify_using_condition): Declare.
> 	* tree-scalar-evolution.c (simple_iv): Simplify type conversions
> 	in iv base using loop initial conditions.
>
> gcc/testsuite/ChangeLog
> 2015-07-28  Bin Cheng  <bin.cheng@arm.com>
>
> 	* gcc.dg/tree-ssa/loop-bound-2.c: New test.
> 	* gcc.dg/tree-ssa/loop-bound-4.c: New test.
> 	* gcc.dg/tree-ssa/loop-bound-6.c: New test.
I have the same concerns about these tests...  Which makes me really 
think I must be mis-understanding something in the debugging output.

jeff