floor operation problem

[bearophile]

While I was debugging a performance problem, I have found the 
cause is the floor operation. Below there is a small benchmark to 
show it.

I have compiled the code with:

gcc -Ofast -std=c99 -s -flto -mfpmath=sse -ffast-math -msse3 
test1.c -o test1
ldmd2 -O -release -inline -noboundscheck test2.d
ldmd2 -O -release -inline -noboundscheck test3.d

32 bit system

gcc version 4.8.0
LDC 0.12.1 (based on DMD v2.063.2 and LLVM 3.3.1)

Run-time, seconds:
test1.c: 1.01
test2.d: 4.14
test3.d: 6.62

---------------------

// test1.c
#include <stdio.h>
#include <math.h>
#include <stdlib.h>

static inline float foo(const float x, const float y) {
     return floorf(x) + floorf(y);
}

int main() {
     float total = 0.0f;

     for (int i = 0; i < 1000; i++)
         for (int y = 0; y < 256; y++)
             for (int x = 0; x < 256; x++)
                 total += foo(x * 0.1f, y * 0.1f);

     printf("%f\n", total);
     return 0;
}

---------------------

// test2.d
import core.stdc.stdio, core.stdc.math;

float foo(const float x, const float y) nothrow {
     return floorf(x) + floorf(y);
}

int main() {
     float total = 0.0f;

     for (int i = 0; i < 1000; i++)
         for (int y = 0; y < 256; y++)
             for (int x = 0; x < 256; x++)
                 total += foo(x * 0.1f, y * 0.1f);

     printf("%f\n", total);
     return 0;
}

---------------------

// test3.d
import core.stdc.stdio, std.math;

float foo(const float x, const float y) nothrow {
     return floor(x) + floor(y);
}

int main() {
     float total = 0.0f;

     for (int i = 0; i < 1000; i++)
         for (int y = 0; y < 256; y++)
             for (int x = 0; x < 256; x++)
                 total += foo(x * 0.1f, y * 0.1f);

     printf("%f\n", total);
     return 0;
}

---------------------

test1.c asm:

_main:
     pushl   %ebp
     movl    %esp, %ebp
     pushl   %ebx
     movl    $1000, %ebx
     andl    $-16, %esp
     subl    $16, %esp
     call    ___main
     xorps   %xmm1, %xmm1
     movss   LC3, %xmm5
L2:
     movss   LC1, %xmm6
     xorps   %xmm3, %xmm3
     xorl    %ecx, %ecx
     .p2align 4,,7
L9:
     movss   LC2, %xmm4
     xorps   %xmm0, %xmm0
     xorl    %eax, %eax
     .p2align 4,,7
L7:
     addss   %xmm0, %xmm1
     addl    $1, %eax
     cmpl    $256, %eax
     addss   %xmm3, %xmm1
     je  L12
     cvtsi2ss    %eax, %xmm0
     mulss   %xmm6, %xmm0
     movaps  %xmm0, %xmm2
     andps   %xmm5, %xmm2
     ucomiss %xmm2, %xmm4
     jbe L7
     cvttss2si   %xmm0, %edx
     cvtsi2ss    %edx, %xmm2
     movaps  %xmm2, %xmm7
     cmpnless    %xmm0, %xmm7
     movaps  %xmm7, %xmm0
     movss   LC4, %xmm7
     andps   %xmm7, %xmm0
     subss   %xmm0, %xmm2
     movaps  %xmm2, %xmm0
     jmp L7
     .p2align 4,,7
L12:
     addl    $1, %ecx
     cmpl    $256, %ecx
     je  L5
     cvtsi2ss    %ecx, %xmm3
     movss   LC6, %xmm0
     movss   LC2, %xmm2
     mulss   LC1, %xmm3
     andps   %xmm3, %xmm0
     ucomiss %xmm0, %xmm2
     jbe L9
     cvttss2si   %xmm3, %eax
     cvtsi2ss    %eax, %xmm0
     movaps  %xmm0, %xmm2
     cmpnless    %xmm3, %xmm2
     movss   LC4, %xmm3
     andps   %xmm3, %xmm2
     movaps  %xmm0, %xmm3
     subss   %xmm2, %xmm3
     jmp L9
L5:
     subl    $1, %ebx
     jne L2
     unpcklps    %xmm1, %xmm1
     movl    $LC5, (%esp)
     cvtps2pd    %xmm1, %xmm5
     movsd   %xmm5, 4(%esp)
     call    _printf
     xorl    %eax, %eax
     movl    -4(%ebp), %ebx
     leave
     ret

---------------------

test2.d asm:

__Dmain:
	pushl	%ebx
	pushl	%edi
	pushl	%esi
	subl	$28, %esp
	xorps	%xmm0, %xmm0
	xorl	%esi, %esi
	movss	LCPI1_0, %xmm1
	.align	16, 0x90
LBB1_1:
	xorl	%edi, %edi
	.align	16, 0x90
LBB1_2:
	xorps	%xmm2, %xmm2
	cvtsi2ssl	%edi, %xmm2
	mulss	%xmm1, %xmm2
	movss	%xmm2, 12(%esp)
	xorl	%ebx, %ebx
	.align	16, 0x90
LBB1_3:
	movss	%xmm0, 16(%esp)
	xorps	%xmm0, %xmm0
	cvtsi2ssl	%ebx, %xmm0
	mulss	%xmm1, %xmm0
	movss	%xmm0, (%esp)
	calll	_floorf
	movss	12(%esp), %xmm0
	movss	%xmm0, (%esp)
	fstps	24(%esp)
	calll	_floorf
	movss	LCPI1_0, %xmm1
	fstps	20(%esp)
	movss	24(%esp), %xmm0
	addss	20(%esp), %xmm0
	movss	16(%esp), %xmm2
	addss	%xmm0, %xmm2
	movss	%xmm2, 16(%esp)
	movss	16(%esp), %xmm0
	incl	%ebx
	cmpl	$256, %ebx
	jne	LBB1_3
	incl	%edi
	cmpl	$256, %edi
	jne	LBB1_2
	incl	%esi
	cmpl	$1000, %esi
	jne	LBB1_1
	cvtss2sd	%xmm0, %xmm0
	movsd	%xmm0, 4(%esp)
	movl	$_.str, (%esp)
	calll	___mingw_printf
	xorl	%eax, %eax
	addl	$28, %esp
	popl	%esi
	popl	%edi
	popl	%ebx
	ret

---------------------

test3.d asm:

__Dmain:
     pushl   %ebx
     pushl   %edi
     pushl   %esi
     subl    $52, %esp
     xorps   %xmm1, %xmm1
     xorl    %esi, %esi
     movss   LCPI1_0, %xmm2
     .align  16, 0x90
LBB1_1:
     xorl    %edi, %edi
     .align  16, 0x90
LBB1_2:
     xorps   %xmm0, %xmm0
     cvtsi2ssl   %edi, %xmm0
     mulss   %xmm2, %xmm0
     movss   %xmm0, 48(%esp)
     xorl    %ebx, %ebx
     flds    48(%esp)
     fstpt   12(%esp)
     movaps  %xmm1, %xmm0
     .align  16, 0x90
LBB1_3:
     movss   %xmm0, 36(%esp)
     xorps   %xmm0, %xmm0
     cvtsi2ssl   %ebx, %xmm0
     mulss   %xmm2, %xmm0
     movss   %xmm0, 44(%esp)
     flds    44(%esp)
     fstpt   (%esp)
     calll   __D3std4math5floorFNbNeeZe
     subl    $12, %esp
     fstpt   24(%esp)
     fldt    12(%esp)
     fstpt   (%esp)
     calll   __D3std4math5floorFNbNeeZe
     subl    $12, %esp
     movss   36(%esp), %xmm0
     movss   LCPI1_0, %xmm2
     fldt    24(%esp)
     faddp   %st(1)
     fstps   40(%esp)
     addss   40(%esp), %xmm0
     incl    %ebx
     cmpl    $256, %ebx
     jne LBB1_3
     movaps  %xmm0, %xmm1
     incl    %edi
     cmpl    $256, %edi
     jne LBB1_2
     incl    %esi
     cmpl    $1000, %esi
     jne LBB1_1
     xorps   %xmm0, %xmm0
     cvtss2sd    %xmm1, %xmm0
     movsd   %xmm0, 4(%esp)
     movl    $_.str, (%esp)
     calll   ___mingw_printf
     xorl    %eax, %eax
     addl    $52, %esp
     popl    %esi
     popl    %edi
     popl    %ebx
     ret

---------------------

Bye,
bearophile