> -----Original Message-----
> From: Andrew Pinski [mailto:pins...@gmail.com]
> Sent: Monday, August 05, 2013 4:40 PM
> To: Zhenqiang Chen
> Cc: GCC Patches
> Subject: Re: [PATCH] Reassociate X == CST1 || X == CST2 if popcount (CST2 -
> CST1) == 1 into ((X - CST1) & ~(CST2 - CST1)) == 0
>
> On Mon, Aug 5, 2013 at 1:08 AM, Zhenqiang Chen
> <zhenqiang.c...@arm.com> wrote:
> > Hi
> >
> > The patch reassociates X == CST1 || X == CST2 if popcount (CST2 -
> > CST1) == 1 into ((X - CST1) & ~(CST2 - CST1)) == 0.
> >
> > Bootstrap on x86-64 and ARM chromebook.
> > No make check regression on x86-64 and panda board.
> >
> > For some targets/options, the "(X == CST1 || X == CST2)" might be
> > converted to "if (x == CST1) else if (x == CST2)" at the beginning. In
> > such case, the patch will not be executed. It is hard to write a
> > reliable testcase to detect the transformation. So the testcase does
> > not check the dump logs from
> > reassoc1 pass. It just checks the runtime result.
> >
> > Is it OK for trunk?
> Seems like a better place to put this is inside tree-ssa-ifcombine.c which
The patch is similar with the code for
Optimize X == CST1 || X == CST2
if popcount (CST1 ^ CST2) == 1 into
(X & ~(CST1 ^ CST2)) == (CST1 & ~(CST1 ^ CST2))
Your "RFC: Gimple combine/folding interface" is a good design.
But before it, I think reusing code in tree-ssa-reassoc.c is the most easy way
to implement it.
> handles the case where if(a || b) is split up into if(a) else if(b).
> Moving it into tree-ssa-ifcombine.c allows for code to be optimized which
> was written using the if(a) else if(b) form.
Yes. There might have opportunities to optimized "if(a) else if(b) form" for
targets which LOGICAL_OP_NON_SHORT_CIRCUIT is FALSE.
If LOGICAL_OP_NON_SHORT_CIRCUIT is TRUE, "a || b" is converted to "a | b" in
fold-const.c if they are simple operands.
Both reassoc and ifcombine optimize short circuiting. But they handle different
scenarios. So I think we need both.
As you had mentioned, we need enhance ifcombine to optimize "if(a) else if(b)
form" using the similar methods from reassoc pass.
> Then it would easier to detect this for all targets and easier to remove from
> fold-const.c the removal of the short circuiting.
A unified interface as your RFC will be helpful for fold-const.c,
tree-ssa-ifcombine.c and tree-ssa-reassoc.c.
If we can detect the optimization opportunity in fold_truth_andor, we do not
need to split if(a || b) into if(a) else if(b) at all.
Thanks!
-Zhenqiang
> > ChangeLog
> > 2013-08-05 Zhenqiang Chen <zhenqiang.c...@arm.com>
> >
> > * tree-ssa-reassoc.c (optimize_range_tests): Reasociate
> > X == CST1 || X == CST2 if popcount (CST2 - CST1) == 1 into
> > ((X - CST1) & ~(CST2 - CST1)) == 0.
> >
> > testsuite/ChangeLog
> > 2013-08-05 Zhenqiang Chen <zhenqiang.c...@arm.com>
> >
> > * gcc.dg/reassoc1.c: New testcase.
