On Mon, Sep 14, 2020 at 5:19 AM Feng Xue OS via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Thanks,
> Feng
>
> ________________________________________
> From: Feng Xue OS <f...@os.amperecomputing.com>
> Sent: Thursday, September 3, 2020 5:29 PM
> To: Richard Biener; gcc-patches@gcc.gnu.org
> Subject: Re: [PATCH 2/2 V3] Simplify plusminus-mult-with-convert expr in
> forwprop (PR 94234)
>
> Attach patch file.
>
> Feng
> ________________________________________
> From: Gcc-patches <gcc-patches-boun...@gcc.gnu.org> on behalf of Feng Xue OS
> via Gcc-patches <gcc-patches@gcc.gnu.org>
> Sent: Thursday, September 3, 2020 5:27 PM
> To: Richard Biener; gcc-patches@gcc.gnu.org
> Subject: [PATCH 2/2 V3] Simplify plusminus-mult-with-convert expr in forwprop
> (PR 94234)
>
> This patch is to handle simplification of plusminus-mult-with-convert
> expression
> as ((T) X) +- ((T) Y), in which at least one of (X, Y) is result of
> multiplication.
> This is done in forwprop pass. We try to transform it to (T) (X +- Y), and
> resort
> to gimple-matcher to fold (X +- Y) instead of manually code pattern
> recognition.
I still don't like the complete new function with all its correctness
issues - the existing
fold_plusminus_mult_expr was difficult enough to get correct for
corner cases and
we do have a set of match.pd patterns (partly?) implementing its transforms.
Looking at
+unsigned goo (unsigned m_param, unsigned n_param)
+{
+ unsigned b1 = m_param * (n_param + 2);
+ unsigned b2 = m_param * (n_param + 1);
+ int r = (int)(b1) - (int)(b2);
it seems we want to simplify (signed)A - (signed)B to
(signed)(A - B) if A - B "simplifies"? I guess
(simplify
(plusminus (nop_convert @0) (nop_convert? @1))
(convert (plusminus! @0 @1)))
probably needs a swapped pattern or not iterate over plus/minus
to handle at least one converted operand and avoid adding
a (plus @0 @1) -> (convert (plus! @0 @1)) rule.
Even
(simplify
(minus (nop_convert @0) (nop_convert @1))
(convert (minus! @0 @1)))
seems to handle all your testcases already (which means
they are all the same and not very exhaustive...)
Richard.
> Regards,
> Feng
> ---
> 2020-09-03 Feng Xue <f...@os.amperecomputing.com>
>
> gcc/
> PR tree-optimization/94234
> * tree-ssa-forwprop.c (simplify_plusminus_mult_with_convert): New
> function.
> (fwprop_ssa_val): Move it before its new caller.
> (pass_forwprop::execute): Add call to
> simplify_plusminus_mult_with_convert.
>
> gcc/testsuite/
> PR tree-optimization/94234
> * gcc.dg/pr94234-3.c: New test.
