void convert44f44d(float *flt, double *dbl) {
  dbl[0] = (double)flt[0];
  dbl[1] = (double)flt[1];
  dbl[2] = (double)flt[2];
  dbl[3] = (double)flt[3];
  dbl[4] = (double)flt[4];
  dbl[5] = (double)flt[5];
  dbl[6] = (double)flt[6];
  dbl[7] = (double)flt[7];
  dbl[8] = (double)flt[8];
  dbl[9] = (double)flt[9];
  dbl[10] = (double)flt[10];
  dbl[11] = (double)flt[11];
  dbl[12] = (double)flt[12];
  dbl[13] = (double)flt[13];
  dbl[14] = (double)flt[14];
  dbl[15] = (double)flt[15];
}


x86 assembly (clang, -O0):
<convert44f44d>:
push   %rbp
mov    %rsp,%rbp
mov    %rdi,-0x8(%rbp)
mov    %rsi,-0x10(%rbp)
mov    -0x8(%rbp),%rax
movss  (%rax),%xmm0
cvtss2sd %xmm0,%xmm0
mov    -0x10(%rbp),%rax
movsd  %xmm0,(%rax)
mov    -0x8(%rbp),%rax
movss  0x4(%rax),%xmm0
cvtss2sd %xmm0,%xmm0
mov    -0x10(%rbp),%rax
movsd  %xmm0,0x8(%rax)
mov    -0x8(%rbp),%rax
movss  0x8(%rax),%xmm0
cvtss2sd %xmm0,%xmm0
mov    -0x10(%rbp),%rax
movsd  %xmm0,0x10(%rax)
mov    -0x8(%rbp),%rax
movss  0xc(%rax),%xmm0
cvtss2sd %xmm0,%xmm0
mov    -0x10(%rbp),%rax
movsd  %xmm0,0x18(%rax)
mov    -0x8(%rbp),%rax
movss  0x10(%rax),%xmm0
cvtss2sd %xmm0,%xmm0
mov    -0x10(%rbp),%rax
movsd  %xmm0,0x20(%rax)
mov    -0x8(%rbp),%rax
movss  0x14(%rax),%xmm0
cvtss2sd %xmm0,%xmm0
mov    -0x10(%rbp),%rax
movsd  %xmm0,0x28(%rax)
mov    -0x8(%rbp),%rax
movss  0x18(%rax),%xmm0
cvtss2sd %xmm0,%xmm0
mov    -0x10(%rbp),%rax
movsd  %xmm0,0x30(%rax)
mov    -0x8(%rbp),%rax
movss  0x1c(%rax),%xmm0
cvtss2sd %xmm0,%xmm0
mov    -0x10(%rbp),%rax
movsd  %xmm0,0x38(%rax)
mov    -0x8(%rbp),%rax
movss  0x20(%rax),%xmm0
cvtss2sd %xmm0,%xmm0
mov    -0x10(%rbp),%rax
movsd  %xmm0,0x40(%rax)
mov    -0x8(%rbp),%rax
movss  0x24(%rax),%xmm0
cvtss2sd %xmm0,%xmm0
mov    -0x10(%rbp),%rax
movsd  %xmm0,0x48(%rax)
mov    -0x8(%rbp),%rax
movss  0x28(%rax),%xmm0
cvtss2sd %xmm0,%xmm0
mov    -0x10(%rbp),%rax
movsd  %xmm0,0x50(%rax)
mov    -0x8(%rbp),%rax
movss  0x2c(%rax),%xmm0
cvtss2sd %xmm0,%xmm0
mov    -0x10(%rbp),%rax
movsd  %xmm0,0x58(%rax)
mov    -0x8(%rbp),%rax
movss  0x30(%rax),%xmm0
cvtss2sd %xmm0,%xmm0
mov    -0x10(%rbp),%rax
movsd  %xmm0,0x60(%rax)
mov    -0x8(%rbp),%rax
movss  0x34(%rax),%xmm0
cvtss2sd %xmm0,%xmm0
mov    -0x10(%rbp),%rax
movsd  %xmm0,0x68(%rax)
mov    -0x8(%rbp),%rax
movss  0x38(%rax),%xmm0
cvtss2sd %xmm0,%xmm0
mov    -0x10(%rbp),%rax
movsd  %xmm0,0x70(%rax)
mov    -0x8(%rbp),%rax
movss  0x3c(%rax),%xmm0
cvtss2sd %xmm0,%xmm0
mov    -0x10(%rbp),%rax
movsd  %xmm0,0x78(%rax)
pop    %rbp
ret

x86 assembly (clang, -O2):
<convert44f44d>:
cvtps2pd (%rdi),%xmm0
movups %xmm0,(%rsi)
cvtps2pd 0x8(%rdi),%xmm0
movups %xmm0,0x10(%rsi)
cvtps2pd 0x10(%rdi),%xmm0
movups %xmm0,0x20(%rsi)
cvtps2pd 0x18(%rdi),%xmm0
movups %xmm0,0x30(%rsi)
cvtps2pd 0x20(%rdi),%xmm0
movups %xmm0,0x40(%rsi)
cvtps2pd 0x28(%rdi),%xmm0
movups %xmm0,0x50(%rsi)
cvtps2pd 0x30(%rdi),%xmm0
movups %xmm0,0x60(%rsi)
cvtps2pd 0x38(%rdi),%xmm0
movups %xmm0,0x70(%rsi)
ret

LLVM IR (-O0):
define void @convert44f44d(float* %0, double* %1) {
%3 = alloca float*
%4 = alloca double*
store float* %0, float** %3
store double* %1, double** %4
%5 = load float*, float** %3
%6 = getelementptr inbounds float, float* %5, i64 0
%7 = load float, float* %6
%8 = fpext float %7 to double
%9 = load double*, double** %4
%10 = getelementptr inbounds double, double* %9, i64 0
store double %8, double* %10
%11 = load float*, float** %3
%12 = getelementptr inbounds float, float* %11, i64 1
%13 = load float, float* %12
%14 = fpext float %13 to double
%15 = load double*, double** %4
%16 = getelementptr inbounds double, double* %15, i64 1
store double %14, double* %16
%17 = load float*, float** %3
%18 = getelementptr inbounds float, float* %17, i64 2
%19 = load float, float* %18
%20 = fpext float %19 to double
%21 = load double*, double** %4
%22 = getelementptr inbounds double, double* %21, i64 2
store double %20, double* %22
%23 = load float*, float** %3
%24 = getelementptr inbounds float, float* %23, i64 3
%25 = load float, float* %24
%26 = fpext float %25 to double
%27 = load double*, double** %4
%28 = getelementptr inbounds double, double* %27, i64 3
store double %26, double* %28
%29 = load float*, float** %3
%30 = getelementptr inbounds float, float* %29, i64 4
%31 = load float, float* %30
%32 = fpext float %31 to double
%33 = load double*, double** %4
%34 = getelementptr inbounds double, double* %33, i64 4
store double %32, double* %34
%35 = load float*, float** %3
%36 = getelementptr inbounds float, float* %35, i64 5
%37 = load float, float* %36
%38 = fpext float %37 to double
%39 = load double*, double** %4
%40 = getelementptr inbounds double, double* %39, i64 5
store double %38, double* %40
%41 = load float*, float** %3
%42 = getelementptr inbounds float, float* %41, i64 6
%43 = load float, float* %42
%44 = fpext float %43 to double
%45 = load double*, double** %4
%46 = getelementptr inbounds double, double* %45, i64 6
store double %44, double* %46
%47 = load float*, float** %3
%48 = getelementptr inbounds float, float* %47, i64 7
%49 = load float, float* %48
%50 = fpext float %49 to double
%51 = load double*, double** %4
%52 = getelementptr inbounds double, double* %51, i64 7
store double %50, double* %52
%53 = load float*, float** %3
%54 = getelementptr inbounds float, float* %53, i64 8
%55 = load float, float* %54
%56 = fpext float %55 to double
%57 = load double*, double** %4
%58 = getelementptr inbounds double, double* %57, i64 8
store double %56, double* %58
%59 = load float*, float** %3
%60 = getelementptr inbounds float, float* %59, i64 9
%61 = load float, float* %60
%62 = fpext float %61 to double
%63 = load double*, double** %4
%64 = getelementptr inbounds double, double* %63, i64 9
store double %62, double* %64
%65 = load float*, float** %3
%66 = getelementptr inbounds float, float* %65, i64 10
%67 = load float, float* %66
%68 = fpext float %67 to double
%69 = load double*, double** %4
%70 = getelementptr inbounds double, double* %69, i64 10
store double %68, double* %70
%71 = load float*, float** %3
%72 = getelementptr inbounds float, float* %71, i64 11
%73 = load float, float* %72
%74 = fpext float %73 to double
%75 = load double*, double** %4
%76 = getelementptr inbounds double, double* %75, i64 11
store double %74, double* %76
%77 = load float*, float** %3
%78 = getelementptr inbounds float, float* %77, i64 12
%79 = load float, float* %78
%80 = fpext float %79 to double
%81 = load double*, double** %4
%82 = getelementptr inbounds double, double* %81, i64 12
store double %80, double* %82
%83 = load float*, float** %3
%84 = getelementptr inbounds float, float* %83, i64 13
%85 = load float, float* %84
%86 = fpext float %85 to double
%87 = load double*, double** %4
%88 = getelementptr inbounds double, double* %87, i64 13
store double %86, double* %88
%89 = load float*, float** %3
%90 = getelementptr inbounds float, float* %89, i64 14
%91 = load float, float* %90
%92 = fpext float %91 to double
%93 = load double*, double** %4
%94 = getelementptr inbounds double, double* %93, i64 14
store double %92, double* %94
%95 = load float*, float** %3
%96 = getelementptr inbounds float, float* %95, i64 15
%97 = load float, float* %96
%98 = fpext float %97 to double
%99 = load double*, double** %4
%100 = getelementptr inbounds double, double* %99, i64 15
store double %98, double* %100
ret void
}

LLVM IR (-O2):
define void @convert44f44d(float* nocapture %0, double* nocapture writeonly %1) {
%3 = bitcast float* %0 to <2 x float>*
%4 = load <2 x float>, <2 x float>* %3
%5 = fpext <2 x float> %4 to <2 x double>
%6 = bitcast double* %1 to <2 x double>*
store <2 x double> %5, <2 x double>* %6
%7 = getelementptr inbounds float, float* %0, i64 2
%8 = getelementptr inbounds double, double* %1, i64 2
%9 = bitcast float* %7 to <2 x float>*
%10 = load <2 x float>, <2 x float>* %9
%11 = fpext <2 x float> %10 to <2 x double>
%12 = bitcast double* %8 to <2 x double>*
store <2 x double> %11, <2 x double>* %12
%13 = getelementptr inbounds float, float* %0, i64 4
%14 = getelementptr inbounds double, double* %1, i64 4
%15 = bitcast float* %13 to <2 x float>*
%16 = load <2 x float>, <2 x float>* %15
%17 = fpext <2 x float> %16 to <2 x double>
%18 = bitcast double* %14 to <2 x double>*
store <2 x double> %17, <2 x double>* %18
%19 = getelementptr inbounds float, float* %0, i64 6
%20 = getelementptr inbounds double, double* %1, i64 6
%21 = bitcast float* %19 to <2 x float>*
%22 = load <2 x float>, <2 x float>* %21
%23 = fpext <2 x float> %22 to <2 x double>
%24 = bitcast double* %20 to <2 x double>*
store <2 x double> %23, <2 x double>* %24
%25 = getelementptr inbounds float, float* %0, i64 8
%26 = getelementptr inbounds double, double* %1, i64 8
%27 = bitcast float* %25 to <2 x float>*
%28 = load <2 x float>, <2 x float>* %27
%29 = fpext <2 x float> %28 to <2 x double>
%30 = bitcast double* %26 to <2 x double>*
store <2 x double> %29, <2 x double>* %30
%31 = getelementptr inbounds float, float* %0, i64 10
%32 = getelementptr inbounds double, double* %1, i64 10
%33 = bitcast float* %31 to <2 x float>*
%34 = load <2 x float>, <2 x float>* %33
%35 = fpext <2 x float> %34 to <2 x double>
%36 = bitcast double* %32 to <2 x double>*
store <2 x double> %35, <2 x double>* %36
%37 = getelementptr inbounds float, float* %0, i64 12
%38 = getelementptr inbounds double, double* %1, i64 12
%39 = bitcast float* %37 to <2 x float>*
%40 = load <2 x float>, <2 x float>* %39
%41 = fpext <2 x float> %40 to <2 x double>
%42 = bitcast double* %38 to <2 x double>*
store <2 x double> %41, <2 x double>* %42
%43 = getelementptr inbounds float, float* %0, i64 14
%44 = getelementptr inbounds double, double* %1, i64 14
%45 = bitcast float* %43 to <2 x float>*
%46 = load <2 x float>, <2 x float>* %45
%47 = fpext <2 x float> %46 to <2 x double>
%48 = bitcast double* %44 to <2 x double>*
store <2 x double> %47, <2 x double>* %48
ret void
}