Re: [RFC][PATCH][PR40921] Convert x + (-y * z * z) into x - y * z * z

[kugan <kugan dot vivekanandarajah at linaro dot org>]

> > I am not sure I understand this. I tried doing this. If I add  -1 and rhs1
> > for the NEGATE_EXPR to ops list,  when it come to rewrite_expr_tree constant
> > will be sorted early and would make it hard to generate:
> >   x + (-y * z * z) => x - y * z * z
> >
> > Do you want to swap the constant in MULT_EXPR chain (if present) like in
> > swap_ops_for_binary_stmt and then create a NEGATE_EXPR ?
>
> In addition to linearize_expr handling you need to handle a -1 in the MULT_EXPR
> chain specially at rewrite_expr_tree time by emitting a NEGATE_EXPR instead
> of a MULT_EXPR (which also means you should sort the -1 "last").

Hi Richard,

Thanks. Here is an attempt which does this.

Regression tested and bootstrapped on x86-64-linux-gnu with no new 
regressions.

Is this OK for trunk?

Thanks,
Kugan

2016-04-23  Kugan Vivekanandarajah  <kuganv@linaro.org>

	PR middle-end/40921
	* gcc.dg/tree-ssa/pr40921.c: New test.

gcc/ChangeLog:

2016-04-23  Kugan Vivekanandarajah  <kuganv@linaro.org>

	PR middle-end/40921
	* tree-ssa-reassoc.c (try_special_add_to_ops): New.
	(linearize_expr_tree): Call try_special_add_to_ops.
	(reassociate_bb): Convert MULT_EXPR by (-1) to NEGATE_EXPR.

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