[Bug c/37807] Exponential compile time with MMX builtins.

[suckfish at ihug dot co dot nz]

--- Comment #1 from suckfish at ihug dot co dot nz  2008-10-11 21:21 ---
Created an attachment (id=16482)
 -- (http://gcc.gnu.org/bugzilla/attachment.cgi?id=16482action=view)
Code showing exponential compile time.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37807

[Bug c/37807] Exponential compile time with MMX builtins.

[suckfish at ihug dot co dot nz]

--- Comment #2 from suckfish at ihug dot co dot nz  2008-10-11 21:35 ---
Using '-da' it looks like the 'combine' pass is the culprit:

$ pidof cc1
6410
$ ls -l /proc/6410/fd
... 4 - ... slow.c.162r.combine
$ ls -s slow.c.162r.combine
0 slow.c.162r.combine

[is there an easier way to get cc1 to tell me what pass it's running when?]


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37807

[Bug c/37807] Exponential compile time with MMX builtins.

[rguenth at gcc dot gnu dot org]

--- Comment #3 from rguenth at gcc dot gnu dot org  2008-10-11 22:06 ---
On the trunk it's fast if you fix the testcase to do

static INLINE value_t ROTATE_LEFT (value_t a, unsigned count)
{
return OR (LEFT (a, ((value_t){count, count})), RIGHT (a,
((value_t){32-count,32-count})));
}


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37807

[Bug c/37807] Exponential compile time with MMX builtins.

[suckfish at ihug dot co dot nz]

--- Comment #4 from suckfish at ihug dot co dot nz  2008-10-11 22:23 ---
BTW, __builtin_ia32_psrld and __builtin_ia32_pslld are not documented on the
'X86 built-in functions' page of the manual.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37807

[Bug c/37807] Exponential compile time with MMX builtins.

[suckfish at ihug dot co dot nz]

--- Comment #5 from suckfish at ihug dot co dot nz  2008-10-11 23:02 ---
It looks like nonzero_bits1 in rtlanal.c is going into an exponential
recursion.

AFAICS, that function doesn't deal properly with vector arithmetic anyway?


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37807

[Bug c/37807] Exponential compile time with MMX builtins.

[suckfish at ihug dot co dot nz]

--- Comment #6 from suckfish at ihug dot co dot nz  2008-10-11 23:24 ---
I think this function actually gets miscompiled:


typedef int v2si __attribute__ ((vector_size (8)));

v2si foo (v2si x)
{
x = (v2si) 0xll;
x = __builtin_ia32_psrad (x, 1);
x = (v2si) 0x8000ll;
return x;
}

to

foo:
pxor%xmm0, %xmm0
ret

The psrad is preserving the sign bit we are returning, so the compiler should
not assume it to be zero.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37807

[Bug c/37807] Exponential compile time with MMX builtins.

[suckfish at ihug dot co dot nz]

--- Comment #7 from suckfish at ihug dot co dot nz  2008-10-12 02:39 ---
Bug 37809 opened for the issue in internal comment 6, as it is different.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37807

[Bug c/37807] Exponential compile time with MMX builtins.

[suckfish at ihug dot co dot nz]

--- Comment #8 from suckfish at ihug dot co dot nz  2008-10-12 04:46 ---
Created an attachment (id=16484)
 -- (http://gcc.gnu.org/bugzilla/attachment.cgi?id=16484action=view)
Test-case modfied to take exponential time on trunk too.

It turns out that it was fast on trunk because inlining is less aggressive
there.

Making some functions inline causes compile time to blow up with trunk also.

Updated test case attached also.

PS.  The correct fix for the rotate on trunk was to use
__builtin_ia32_psrldi/pslldi.


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suckfish at ihug dot co dot nz changed:

   What|Removed |Added

  Attachment #16482|0   |1
is obsolete||


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37807

[Bug c/37807] Exponential compile time with MMX builtins.

[suckfish at ihug dot co dot nz]

--- Comment #9 from suckfish at ihug dot co dot nz  2008-10-12 05:22 ---
Created an attachment (id=16486)
 -- (http://gcc.gnu.org/bugzilla/attachment.cgi?id=16486action=view)
Possible fix for 37807

Patch above essentially stops nonzero_bits1 and num_sign_bit_copies1 processing
vector types.

This fixes the problem  looking at those functions, they were not written with
vector types in mind.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37807

[Bug c/37807] Exponential compile time with MMX builtins.

[suckfish at ihug dot co dot nz]

--- Comment #10 from suckfish at ihug dot co dot nz  2008-10-12 05:27 
---
Changelog for patch if accepted [will do full bootstrap  make test]:

2008-10-12  Ralph Loader  [EMAIL PROTECTED]

PR 37807
* rtlanal.c (numzero_bits1): Return early on vector types, avoiding
exponential time recursion.
(num_sign_bit_copies1): Likewise.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37807