http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55662
Bug #: 55662
Summary: SLP vectorization of sqrt fails if in a loop
Classification: Unclassified
Product: gcc
Version: 4.8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
given the code below
computeOne vectorizes, computeS does not
c++ -std=c++11 -Ofast -mavx2 -S sqrtV.cc; less sqrtV.s
gcc version 4.8.0 20121212 (experimental) [trunk revision 194442] (GCC)
funny enough it works with arbitrary (inlined) functions of mine (instead of
sqrtf) see computeA
computeL does "vectorize", not in the way I expected!
I really do not understand the code generated for computeAL
cat >> sqrtV.cc
#include<cmath>
#include<type_traits>
typedef float __attribute__( ( vector_size( 16 ) ) ) float32x4_t;
typedef float __attribute__( ( vector_size( 32 ) ) ) float32x8_t;
typedef int __attribute__( ( vector_size( 32 ) ) ) int32x8_t;
float32x8_t va[1024];
float32x8_t vb[1024];
float32x8_t vc[1024];
template<typename Vec, typename F>
inline
Vec apply(Vec v, F f) {
typedef typename std::remove_reference<decltype(v[0])>::type T;
constexpr int N = sizeof(Vec)/sizeof(T);
Vec ret;
for (int i=0;i!=N;++i) ret[i] = f(v[i]);
return ret;
}
void computeOne() {
vb[0]=apply(va[0],sqrtf);
}
void computeS() {
for (int i=0;i!=1024;++i)
vb[i]=apply(va[i],sqrtf);
}
void computeL() {
for (int i=0;i!=1024;++i)
for (int j=0;j!=8;++j)
vb[i][j]=sqrtf(va[i][j]);
}
template<typename Float>
inline
Float atanF(Float t) {
constexpr float PIO4F = 0.7853981633974483096f;
Float z= (t > 0.4142135623730950f) ? (t-1.0f)/(t+1.0f) : t;
// if( t > 0.4142135623730950f ) // * tan pi/8
Float z2 = z * z;
Float ret =
((( 8.05374449538e-2f * z2
- 1.38776856032E-1f) * z2
+ 1.99777106478E-1f) * z2
- 3.33329491539E-1f) * z2 * z
+ z;
// move back in place
return ( t > 0.4142135623730950f ) ? ret : ret + PIO4F;
return ret;
}
void computeA() {
for (int i=0;i!=1024;++i)
vb[i]=apply(va[i],atanF<float>);
}
void computeAL() {
for (int i=0;i!=1024;++i)
for (int j=0;j!=8;++j)
vb[i][j]=atanF(va[i][j]);
}
