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[Bug c++/31802] New: SSE2 performance is deteriorating when __m128 is placed in union
- From: "yuri at tsoft dot com" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 3 May 2007 18:27:37 -0000
- Subject: [Bug c++/31802] New: SSE2 performance is deteriorating when __m128 is placed in union
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
When I compile the following testcase with '-O3 -msse3' options it runs in
22.562sec, without 'union' clause it runs in 0.280sec. And should be the same
time.
-- begin testcase --
typedef float __v2df __attribute__ ((__vector_size__ (16)));
typedef __v2df __m128;
static __inline __m128 _mm_sub_pd (__m128 __A, __m128 __B) { return
(__m128)__builtin_ia32_subps ((__v2df)__A, (__v2df)__B); }
static __inline __m128 _mm_add_pd (__m128 __A, __m128 __B) { return
(__m128)__builtin_ia32_addps ((__v2df)__A, (__v2df)__B); }
static __inline __m128 _mm_setr_ps (float __Z, float __Y, float __X, float __W)
{ return __extension__ (__m128)(__v2df){ __Z, __Y, __X, __W }; }
struct FF {
union {__m128 d; float f[4];}; // problem
// __m128 d; // no problem
__inline FF() { }
__inline FF(__m128 new_d) : d(new_d) { }
__inline FF(float f) : d(_mm_setr_ps(f, f, f, f)) { }
__inline FF operator+(FF other) { return (FF(_mm_add_pd(d,other.d))); }
__inline FF operator-(FF other) { return (FF(_mm_sub_pd(d,other.d))); }
};
float f[1024*1024];
int main() {
int i;
for (i = 0; i < 1024*1024; i++) { f[i] = 1.f/(1024*1024 + 10 - i); }
FF total(0.f);
for (int rpt = 0; rpt < 1000; rpt++) {
FF p1(0.f), p2(0.), c;
__m128 *pf = (__m128*)f;
for (i = 0; i < 1024*1024/4; i++) {
FF c(*pf++);
total = total + c - p2 + p1;
p1 = p2;
p2 = c;
}
}
}
-- end testcase
This bug has similar testcase as 25500 (that's fixed now). Only 'union' clause
was added.
Yuri
--
Summary: SSE2 performance is deteriorating when __m128 is placed
in union
Product: gcc
Version: 4.1.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: yuri at tsoft dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31802