Re: [PATCH V3][GCC] Algorithmic optimization in match and simplify

[James Greenhalgh <james.greenhalgh@arm.com>]

On Thu, Oct 08, 2015 at 01:29:34PM +0100, Richard Biener wrote:
> > Thanks again for the comments Richard!
> >
> > A new algorithmic optimisation:
> >
> > ((X inner_op C0) outer_op C1)
> > With X being a tree where value_range has reasoned certain bits to always be
> > zero throughout its computed value range, we will call this the zero_mask,
> > and with inner_op = {|,^}, outer_op = {|,^} and inner_op != outer_op.
> > if (inner_op == '^') C0 &= ~C1;
> > if ((C0 & ~zero_mask) == 0) then emit (X outer_op (C0 outer_op C1)
> > if ((C1 & ~zero_mask) == 0) then emit (X inner_op (C0 outer_op C1)
> >
> > And extended '(X & C2) << C1 into (X << C1) & (C2 << C1)' and
> > '(X & C2) >> C1 into (X >> C1) & (C2 >> C1)' to also accept the bitwise or
> > and xor operators:
> > '(X {&,^,|} C2) << C1 into (X << C1) {&,^,|} (C2 << C1)' and
> > '(X {&,^,|} C2) >> C1 into (X >> C1) & (C2 >> C1)'.
> >
> > The second transformation enables more applications of the first. Also some
> > targets may benefit from delaying shift operations. I am aware that such an
> > optimization, in combination with one or more optimizations that cause the
> > reverse transformation, may lead to an infinite loop. Though such behavior
> > has not been detected during regression testing and bootstrapping on
> > aarch64.
> >
> > gcc/ChangeLog:
> >
> > 2015-10-05 Andre Vieira <andre.simoesdiasvieira@arm.com>
> >
> > * match.pd: Added a new pattern
> > ((X inner_op C0) outer_op C1)
> > and expanded existing one
> > (X {|,^,&} C0) {<<,>>} C1 -> (X {<<,>>} C1) {|,^,&} (C0 {<<,>>} C1)
> >
> > gcc/testsuite/ChangeLog:
> >
> > 2015-10-05 Andre Vieira <andre.simoesdiasvieira@arm.com>
> >
> > Hale Wang <hale.wang@arm.com>
> >
> > * gcc.dg/tree-ssa/forwprop-33.c: New test.
> 
> Ok.
> 
> Thanks,
> Richard.
> 

As Andre does not have commit rights, I've committed this on his behalf as
revision 228661. Please watch for any fallout over the weekend.

Andre, please check your ChangeLog format in future. In the end I
committed this:

gcc/ChangeLog

2015-10-09  Andre Vieira  <andre.simoesdiasvieira@arm.com>

	* match.pd: ((X inner_op C0) outer_op C1) New pattern.
	((X & C2) << C1): Expand to...
	(X {&,^,|} C2 << C1): ...This.
	((X & C2) >> C1): Expand to...
	(X {&,^,|} C2 >> C1): ...This.

gcc/testsuite/ChangeLog

2015-10-09  Andre Vieira  <andre.simoesdiasvieira@arm.com>
	    Hale Wang  <hale.wang@arm.com>

	* gcc.dg/tree-ssa/forwprop-33.c: New.

Thanks,
James