Bug 5254 – Low performance code with struct constructor

This D2 test program contains a Foo struct that is a minimized version of a common 3D vector struct. A static if switches between a normal constructor and no constructor with default initialization of the tree coordiates. enum bool use_ctor = true; struct Foo { static if (use_ctor) { double x, y, z; pure nothrow this(double x_, double y_, double z_) { this.x = x_; this.y = y_; this.z = z_; } } else { double x=0.0, y=0.0, z=0.0; } Foo muls(double s) { return Foo(this.x*s, this.y*s, this.z*s); } } void main() {} I have compiled the two versions using DMD 2.050 with dmd -O -release -inline The resulting asm shows a significant difference. The full program that uses the 3D vectors too shows a different performance in the cases: ----------------------- use_ctor=true: _D4test3Foo6__ctorMFNaNbNcdddZS4test3Foo comdat assume CS:_D4test3Foo6__ctorMFNaNbNcdddZS4test3Foo mov ECX,EAX fld qword ptr 014h[ESP] fld qword ptr 0Ch[ESP] fld qword ptr 4[ESP] fxch ST2 fstp qword ptr [ECX] fstp qword ptr 8[ECX] fstp qword ptr 010h[ECX] ret 018h _D4test3Foo6__ctorMFNaNbNcdddZS4test3Foo ends _D4test3Foo4mulsMFdZS4test3Foo comdat assume CS:_D4test3Foo4mulsMFdZS4test3Foo sub ESP,028h mov ECX,EAX push ESI mov ESI,offset FLAT:_D4test3Foo6__initZ push EDI lea EDI,8[ESP] movsd movsd movsd movsd movsd movsd fld qword ptr 8[ECX] fld qword ptr 010h[ECX] fxch ST1 fmul qword ptr 038h[ESP] lea ESI,8[ESP] mov EDI,034h[ESP] fxch ST1 fmul qword ptr 038h[ESP] fld qword ptr [ECX] fmul qword ptr 038h[ESP] fxch ST2 fstp qword ptr 020h[ESP] fxch ST1 fld qword ptr 020h[ESP] fxch ST2 fstp qword ptr 028h[ESP] fxch ST1 fld qword ptr 028h[ESP] fxch ST2 fstp qword ptr 8[ESP] fstp qword ptr 010h[ESP] fstp qword ptr 018h[ESP] movsd movsd movsd movsd movsd movsd mov EAX,034h[ESP] pop EDI pop ESI add ESP,028h ret 0Ch _D4test3Foo4mulsMFdZS4test3Foo ends ----------------------- use_ctor=false: _D4test3Foo4mulsMFdZS4test3Foo comdat assume CS:_D4test3Foo4mulsMFdZS4test3Foo mov ECX,EAX mov EDX,4[ESP] mov EAX,EDX fld qword ptr [ECX] fmul qword ptr 8[ESP] fstp qword ptr [EDX] fld qword ptr 8[ECX] fmul qword ptr 8[ESP] fstp qword ptr 8[EDX] fld qword ptr 010h[ECX] fmul qword ptr 8[ESP] fstp qword ptr 010h[EDX] ret 0Ch _D4test3Foo4mulsMFdZS4test3Foo ends ----------------------- Using LDC1: _D7path13e2V34mulsMFdZS7path13e2V3: movsd 8(%esp), %xmm0 movapd %xmm0, %xmm1 mulsd 16(%eax), %xmm1 movapd %xmm0, %xmm2 mulsd 8(%eax), %xmm2 mulsd (%eax), %xmm0 movl 4(%esp), %eax movsd %xmm0, (%eax) movsd %xmm2, 8(%eax) movsd %xmm1, 16(%eax) ret $12

THIS ISSUE HAS BEEN MOVED TO GITHUB https://github.com/dlang/dmd/issues/18317 DO NOT COMMENT HERE ANYMORE, NOBODY WILL SEE IT, THIS ISSUE HAS BEEN MOVED TO GITHUB