| Summary: | 387 constants still emitted with -mno-80387 & -mfpmath=sse | ||
|---|---|---|---|
| Product: | gcc | Reporter: | tbp <tbptbp> |
| Component: | target | Assignee: | Not yet assigned to anyone <unassigned> |
| Status: | RESOLVED FIXED | ||
| Severity: | enhancement | CC: | gcc-bugs |
| Priority: | P3 | Keywords: | missed-optimization, ssemmx |
| Version: | 4.0.0 | ||
| Target Milestone: | 4.0.0 | ||
| Host: | cygwin | Target: | |
| Build: | Known to work: | ||
| Known to fail: | Last reconfirmed: | ||
I would doubt this is target related but really the register allocator sucking. This has been fixed now on the mainline:
subss 8(%rsi), %xmm7
movss .LC1(%rip), %xmm6
movss .LC0(%rip), %xmm11
movss 4(%rdx), %xmm2
(In reply to comment #2) > This has been fixed now on the mainline: Note I copied the wrong asm: pushl %ebx .LCFI5: movl $0x3f800000, %ebx subl $8, %esp .LCFI6: movl 16(%esp), %eax movl 20(%esp), %edx movl 24(%esp), %ecx movl %ebx, 4(%esp) movss 4(%eax), %xmm4 pushl %ebx .LCFI3: movl $0x3f800000, %ebx subl $16, %esp .LCFI4: movl 24(%esp), %eax movl 28(%esp), %edx movl 32(%esp), %ecx movss 4(%eax), %xmm2 movss (%eax), %xmm4 subss 4(%edx), %xmm2 But it is still fixed. |
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).