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* [Bug target/55303] New: [SH] Add support for clips / clipu instructions
@ 2012-11-13 0:31 olegendo at gcc dot gnu.org
2013-03-02 16:17 ` [Bug target/55303] " olegendo at gcc dot gnu.org
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: olegendo at gcc dot gnu.org @ 2012-11-13 0:31 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55303
Bug #: 55303
Summary: [SH] Add support for clips / clipu instructions
Classification: Unclassified
Product: gcc
Version: 4.8.0
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: target
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: olegendo@gcc.gnu.org
Target: sh2a*-*-*
Support for the following SH2A specific instructions should be added:
clips.b Rn
clips.w Rn
clipu.b Rn
clipu.w Rn
These can be used to implement saturating arithmetic, for example.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug target/55303] [SH] Add support for clips / clipu instructions
2012-11-13 0:31 [Bug target/55303] New: [SH] Add support for clips / clipu instructions olegendo at gcc dot gnu.org
@ 2013-03-02 16:17 ` olegendo at gcc dot gnu.org
2013-03-02 16:24 ` olegendo at gcc dot gnu.org
2013-05-06 5:48 ` olegendo at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: olegendo at gcc dot gnu.org @ 2013-03-02 16:17 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55303
Oleg Endo <olegendo at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |ASSIGNED
Last reconfirmed| |2013-03-02
AssignedTo|unassigned at gcc dot |olegendo at gcc dot gnu.org
|gnu.org |
Ever Confirmed|0 |1
--- Comment #1 from Oleg Endo <olegendo at gcc dot gnu.org> 2013-03-02 16:16:41 UTC ---
Created attachment 29567
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29567
Working patch with a thinko.
This patch, albeit working, has a thinko.
The idea was to reduce the constraints of the clips/clipu insn comparison
constants by adding/subtracting a constant offset value before/after the actual
clipping insn. For example:
int
test_02 (int a)
{
return max (0, min (255, a));
}
becomes:
_test_02:
movi20 #128,r1
sub r1,r4
mov r4,r0
clips.b r0
rts
add r1,r0
The problem with this is that it won't work for values that will wrap-around
before/after the offset subtraction/addition.
E.g. plugging the value 0x80000000 (−2147483648) into the above case:
movi20 #128,r1
sub r1,r4 // r4 = 0x80000000 - 128 = 0x7FFFFF80
mov r4,r0
clips.b r0 // !(r0 < -128) && (r0 > 127) -> r0 = 127
rts
add r1,r0 // r0 = 127 + 128 = 255
// expected result: 0
Maybe this case could be handled by using subv/addv insns to catch
over/underflows somehow, but probably the resulting code would be more complex
(and thus slower) than two straight forward compare-and-branch sequences.
On the other hand, if it is known that the input value is in a certain range
(e.g. a sign/zero extended HImode or QImode), the offset approach should work
fine.
I will modify the attached patch so that it will allow only the HW clip
constants for now.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug target/55303] [SH] Add support for clips / clipu instructions
2012-11-13 0:31 [Bug target/55303] New: [SH] Add support for clips / clipu instructions olegendo at gcc dot gnu.org
2013-03-02 16:17 ` [Bug target/55303] " olegendo at gcc dot gnu.org
@ 2013-03-02 16:24 ` olegendo at gcc dot gnu.org
2013-05-06 5:48 ` olegendo at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: olegendo at gcc dot gnu.org @ 2013-03-02 16:24 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55303
--- Comment #2 from Oleg Endo <olegendo at gcc dot gnu.org> 2013-03-02 16:23:57 UTC ---
For non-SH2A targets there is an opportunity to generate better insn sequences
for the special case
unsigned int test (unsigned int a)
{
return a > 1 ? 1 : a;
}
on SH2A:
tst r4,r4
movrt r0
if zero-displacement branches are not good:
tst r4,r4
mov #-1,r0
negc r0,r0
if zero-displacement branches are good:
tst r4,r4
bt 0f
mov #1,r1
0f:
This can be done by implementing a pattern
(umin:SI (match_operand:SI 1 "arith_reg_operand")
(const_int 1))
as it is already done for SH2A in attachment 29567.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug target/55303] [SH] Add support for clips / clipu instructions
2012-11-13 0:31 [Bug target/55303] New: [SH] Add support for clips / clipu instructions olegendo at gcc dot gnu.org
2013-03-02 16:17 ` [Bug target/55303] " olegendo at gcc dot gnu.org
2013-03-02 16:24 ` olegendo at gcc dot gnu.org
@ 2013-05-06 5:48 ` olegendo at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: olegendo at gcc dot gnu.org @ 2013-05-06 5:48 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55303
--- Comment #3 from Oleg Endo <olegendo at gcc dot gnu.org> 2013-05-06 05:48:18 UTC ---
(In reply to comment #1)
> I will modify the attached patch so that it will allow only the HW clip
> constants for now.
This has been committed as rev 198617:
http://gcc.gnu.org/viewcvs/gcc?view=revision&revision=198617
PR target/55303
* config/sh/sh.c (sh_rtx_costs): Handle SMIN and SMAX cases.
* config/sh/sh.md (*clips, uminsi3, *clipu, clipu_one): New insns and
related expanders.
* config/sh/iterators.md (SMIN_SMAX): New code iterator.
* config/sh/predicates.md (arith_reg_or_0_or_1_operand,
clips_min_const_int, clips_max_const_int, clipu_max_const_int):
New predicates.
PR target/55303
* gcc.target/sh/pr55303-1.c: New.
* gcc.target/sh/pr55303-2.c: New.
* gcc.target/sh/pr55303-3.c: New.
^ permalink raw reply [flat|nested] 4+ messages in thread
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2012-11-13 0:31 [Bug target/55303] New: [SH] Add support for clips / clipu instructions olegendo at gcc dot gnu.org
2013-03-02 16:17 ` [Bug target/55303] " olegendo at gcc dot gnu.org
2013-03-02 16:24 ` olegendo at gcc dot gnu.org
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