[Bug rtl-optimization/19463] New: 387 constants still emitted with -mno-80387 & -mfpmath=sse

[tbptbp at gmail dot com]

Under elusive conditions, hence the rather cluttered testcase, i'm seeing some
387 constants being used here and there; it doesn't have a big performance
impact but it's not uncommon or correct :)

Happens on gcc-40102 and a 2 day old cvs version (post SSE audit).

With: -O2 -march=k8 -fomit-frame-pointer -mfpmath=sse -mno-80387
[-mno-fancy-math-387]
#include <math.h>

struct vec_t {
       float x,y,z;
       vec_t() {}
       vec_t(const float f1,const float f2,const float f3) : x(f1),y(f2),z(f3) {}

       vec_t operator *(const float f)  const { return vec_t(x*f,y*f,z*f); }
       vec_t operator -(const vec_t &v) const { return vec_t(x-v.x,y-v.y,z-v.z); }
       float mag() const { return sqrtf(x*x + y*y + z*z); }
       vec_t normalize() const { return *this * (1.f/mag()); }
       vec_t cross(const vec_t &v) const { return vec_t(y*v.z - z*v.y,z*v.x
- x*v.z, x*v.y - y*v.x); }
};

// needs -O >= 2
void fpu_constant(vec_t &v1, vec_t &v2, vec_t &v3) {
       const vec_t
               d       = (v1-v2).normalize(),
               r       = v3.cross(d).normalize(),
               u       = d.cross(r).normalize();

       v1 = d; v2 = r; v3 = u;
}

// while making the testcase also found that; needs -O >=1
void fpu_load_store(vec_t &v1, vec_t &v2, vec_t &v3) {
       const vec_t
               d       = (v1-v2).normalize(),
               r       = v3.cross(d).normalize(),
               u;//    = d.cross(r).normalize();

       v1 = d; v2 = r; v3 = u;
}

int main() { return 0; }

In fpu_constant i'm seeing:
 401073:       fld1
...
 4010ba:       movss  0x402000,%xmm1
 4010c2:       sqrtss %xmm0,%xmm0
 4010c6:       divss  %xmm0,%xmm1
...
 401123:       fstps  (%esp)
...
 4011c0:       movss  (%esp),%xmm1
 4011c5:       sqrtss %xmm0,%xmm0
 4011c9:       divss  %xmm0,%xmm1

While making that testcase, i've stumbled upon fpu_load_store:
 401220:       flds   0x402004
...
 401325:       fsts   0x8(%ecx)
 401328:       fsts   0x4(%ecx)
 40132b:       fstps  (%ecx)
 40132d:       add    $0x8,%esp
 401330:       pop    %ebx
 401331:       ret

I've also spotted an fldz on occasion (but not in this testcase).

-- 
           Summary: 387 constants still emitted with -mno-80387 & -
                    mfpmath=sse
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: tbptbp at gmail dot com
                CC: gcc-bugs at gcc dot gnu dot org
  GCC host triplet: cygwin


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19463