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Re: [PATCH] Factor out division by squares and remove division around comparisons (0/2)
- From: Jackson Woodruff <jackson dot woodruff at foss dot arm dot com>
- To: Jeff Law <law at redhat dot com>, GCC Patches <gcc-patches at gcc dot gnu dot org>
- Cc: Wilco Dijkstra <Wilco dot Dijkstra at arm dot com>, Richard Biener <richard dot guenther at gmail dot com>, "kyrylo dot tkachov at foss dot arm dot com" <kyrylo dot tkachov at foss dot arm dot com>, "Joseph S. Myers" <joseph at codesourcery dot com>
- Date: Wed, 13 Sep 2017 10:22:05 +0100
- Subject: Re: [PATCH] Factor out division by squares and remove division around comparisons (0/2)
- Authentication-results: sourceware.org; auth=none
- References: <a97a80c5-c2a9-86de-5152-cd1207036592@foss.arm.com> <9856f0ec-7a54-b918-b654-6cc08aa106dc@redhat.com>
On 09/12/2017 11:43 PM, Jeff Law wrote:
On 09/06/2017 03:54 AM, Jackson Woodruff wrote:
Hi all,
This patch is split from part (1/2). It includes the patterns that have
been moved out of fold-const.c
It also removes an (almost entirely) redundant pattern:
(A / C1) +- (A / C2) -> A * (1 / C1 +- 1 / C2)
which was only used in special cases, either with combinations
of flags like -fno-reciprocal-math -funsafe-math-optimizations
and cases where C was sNaN, or small enough to result in infinity.
This pattern is covered by:
(A / C1) +- (A / C2) -> (with O1 and reciprocal math)
A * (1 / C1) +- A * (1 / C2) ->
A * (1 / C1 +- 1 / C2)
The previous pattern required funsafe-math-optimizations.
To adjust for this case, the testcase has been updated to require O1 so
that the optimization is still performed.
This pattern is moved verbatim into match.pd:
(A / C) +- (B / C) -> (A +- B) / C.
OK for trunk?
Jackson
gcc/
2017-08-30 Jackson Woodruff <jackson.woodruff@arm.com>
PR 71026/tree-optimization
* match.pd: Move RDIV patterns from fold-const.c
* fold-const.c (distribute_real_division): Removed.
(fold_binary_loc): Remove calls to distribute_real_divison.
gcc/testsuite/
2017-08-30 Jackson Woodruff <jackson.woodruff@arm.com>
PR 71026/tree-optimization
* gcc/testsuire/gcc.dg/fold-div-1.c: Use O1.
Didn't you lose the case where the operator is MULT_EXPR rather than
RDIV_EXPR?
If I'm reading things correctly, arg0 and arg1 could be a RDIV_EXPR or a
MULT_EXPR and we distribute both cases (as long as they are both the
same code). >
Your match.pd pattern only handle rdiv.
In the fold_plusminus_mult_expr function in fold-const.c, we still do
the simplification:
(A * C) +- (B * C) -> (A+-B) * C
So the pattern I introduced only needs to handle the division case.
Now it may be the case that MULT_EXPR doesn't happen anymore in practice
-- the code in fold-const is quote old and much of it was written before
we regularly added tests for optimization and canonicalization. So I'm
not surprised nothing in this testsuite trips over this omission.
In gcc.dg/fold-plusmult.c, we test whether 2*a + 2*a is folded into a *
4, which comes close.
There are also a few tests for this in gcc.dg/tree-ssa/pr23294.c,
although again, they are use constants for A and B.
I verified that
x * y + z * y
Gets folded into
y * (x + z)
ISTM you need to either argue that the MULT_EXPR case is handled
elsewhere or that it is no longer relevant.
jeff