__builtin_expect comparison

gcc_readdir.diff

--- readdir.s   2012-07-03 16:24:35.568018624 +0000
+++ readdir_o.s 2012-07-03 16:24:06.528020576 +0000
@@ -12,9 +12,9 @@
        movl    16(%rdi), %edx
        movq    %rdi, %rbx
        cmpl    20(%rdi), %edx
+       jge     .L7
+.L2:
        movslq  %edx, %rax
-       jge     .L8
-.L3:
        leaq    32(%rbx,%rax), %rax
        movzwl  16(%rax), %ecx
        addl    %ecx, %edx
@@ -25,26 +25,22 @@
        .cfi_remember_state
        .cfi_def_cfa_offset 8
        ret
-       .p2align 4,,10
-       .p2align 3
-.L8:
+.L7:
        .cfi_restore_state
        leaq    32(%rdi), %rsi
        movl    (%rdi), %edi
        movl    $2048, %edx
        call    __getdents
        testl   %eax, %eax
-       jle     .L5
+       jle     .L4
        movl    %eax, 20(%rbx)
        xorl    %edx, %edx
-       xorl    %eax, %eax
-       jmp     .L3
-       .p2align 4,,10
-       .p2align 3
-.L5:
+       jmp     .L2
+.L4:
        xorl    %eax, %eax
        popq    %rbx
        .cfi_def_cfa_offset 8
+       .p2align 4,,1
        ret
        .cfi_endproc
 .LFE7:

gcc_readdir.s

        .file   "readdir.c"
        .text
        .p2align 4,,15
        .globl  readdir
        .type   readdir, @function
readdir:
.LFB7:
        .cfi_startproc
        pushq   %rbx
        .cfi_def_cfa_offset 16
        .cfi_offset 3, -16
        movl    16(%rdi), %edx
        movq    %rdi, %rbx
        cmpl    20(%rdi), %edx
        movslq  %edx, %rax
        jge     .L8
.L3:
        leaq    32(%rbx,%rax), %rax
        movzwl  16(%rax), %ecx
        addl    %ecx, %edx
        movl    %edx, 16(%rbx)
        movq    8(%rax), %rdx
        movq    %rdx, 8(%rbx)
        popq    %rbx
        .cfi_remember_state
        .cfi_def_cfa_offset 8
        ret
        .p2align 4,,10
        .p2align 3
.L8:
        .cfi_restore_state
        leaq    32(%rdi), %rsi
        movl    (%rdi), %edi
        movl    $2048, %edx
        call    __getdents
        testl   %eax, %eax
        jle     .L5
        movl    %eax, 20(%rbx)
        xorl    %edx, %edx
        xorl    %eax, %eax
        jmp     .L3
        .p2align 4,,10
        .p2align 3
.L5:
        xorl    %eax, %eax
        popq    %rbx
        .cfi_def_cfa_offset 8
        ret
        .cfi_endproc
.LFE7:
        .size   readdir, .-readdir
        .weak   readdir64
        .set    readdir64,readdir
        .ident  "GCC: (Exherbo gcc-4.7.1) 4.7.1"
        .section        .note.GNU-stack,"",@progbits

gcc_readdir_o.s

        .file   "readdir.c"
        .text
        .p2align 4,,15
        .globl  readdir
        .type   readdir, @function
readdir:
.LFB7:
        .cfi_startproc
        pushq   %rbx
        .cfi_def_cfa_offset 16
        .cfi_offset 3, -16
        movl    16(%rdi), %edx
        movq    %rdi, %rbx
        cmpl    20(%rdi), %edx
        jge     .L7
.L2:
        movslq  %edx, %rax
        leaq    32(%rbx,%rax), %rax
        movzwl  16(%rax), %ecx
        addl    %ecx, %edx
        movl    %edx, 16(%rbx)
        movq    8(%rax), %rdx
        movq    %rdx, 8(%rbx)
        popq    %rbx
        .cfi_remember_state
        .cfi_def_cfa_offset 8
        ret
.L7:
        .cfi_restore_state
        leaq    32(%rdi), %rsi
        movl    (%rdi), %edi
        movl    $2048, %edx
        call    __getdents
        testl   %eax, %eax
        jle     .L4
        movl    %eax, 20(%rbx)
        xorl    %edx, %edx
        jmp     .L2
.L4:
        xorl    %eax, %eax
        popq    %rbx
        .cfi_def_cfa_offset 8
        .p2align 4,,1
        ret
        .cfi_endproc
.LFE7:
        .size   readdir, .-readdir
        .weak   readdir64
        .set    readdir64,readdir
        .ident  "GCC: (Exherbo gcc-4.7.1) 4.7.1"
        .section        .note.GNU-stack,"",@progbits

llvm_readdir.s

        .file   "src/dirent/readdir.c"
        .text
        .globl  readdir
        .align  16, 0x90
        .type   readdir,@function
readdir:                                # @readdir
        .cfi_startproc
# BB#0:
        pushq   %rbx
.Ltmp2:
        .cfi_def_cfa_offset 16
.Ltmp3:
        .cfi_offset %rbx, -16
        movq    %rdi, %rbx
        movl    16(%rbx), %eax
        cmpl    20(%rbx), %eax
        jl      .LBB0_3
# BB#1:
        movl    (%rbx), %edi
        leaq    32(%rbx), %rsi
        movl    $2048, %edx             # imm = 0x800
        callq   __getdents
        movl    %eax, %ecx
        xorl    %eax, %eax
        testl   %ecx, %ecx
        jle     .LBB0_4
# BB#2:
        movl    %ecx, 20(%rbx)
        movl    $0, 16(%rbx)
        xorl    %eax, %eax
.LBB0_3:
        movslq  %eax, %rax
        movzwl  48(%rbx,%rax), %ecx
        movl    %eax, %edx
        addl    %ecx, %edx
        movl    %edx, 16(%rbx)
        movq    40(%rbx,%rax), %rcx
        movq    %rcx, 8(%rbx)
        leaq    32(%rbx,%rax), %rax
.LBB0_4:
        popq    %rbx
        ret
.Ltmp4:
        .size   readdir, .Ltmp4-readdir
        .cfi_endproc


        .weak   readdir64
readdir64 = readdir
        .section        ".note.GNU-stack","",@progbits

llvm_readdir_o.s

        .file   "src/dirent/readdir.c"
        .text
        .globl  readdir
        .align  16, 0x90
        .type   readdir,@function
readdir:                                # @readdir
        .cfi_startproc
# BB#0:
        pushq   %rbx
.Ltmp2:
        .cfi_def_cfa_offset 16
.Ltmp3:
        .cfi_offset %rbx, -16
        movq    %rdi, %rbx
        movl    16(%rbx), %eax
        cmpl    20(%rbx), %eax
        jge     .LBB0_1
        .align  16, 0x90
.LBB0_3:
        movslq  %eax, %rax
        movzwl  48(%rbx,%rax), %ecx
        movl    %eax, %edx
        addl    %ecx, %edx
        movl    %edx, 16(%rbx)
        movq    40(%rbx,%rax), %rcx
        movq    %rcx, 8(%rbx)
        leaq    32(%rbx,%rax), %rax
        .align  16, 0x90
.LBB0_4:
        popq    %rbx
        ret
.LBB0_1:
        movl    (%rbx), %edi
        leaq    32(%rbx), %rsi
        movl    $2048, %edx             # imm = 0x800
        callq   __getdents
        movl    %eax, %ecx
        xorl    %eax, %eax
        testl   %ecx, %ecx
        jle     .LBB0_4
# BB#2:
        movl    %ecx, 20(%rbx)
        movl    $0, 16(%rbx)
        xorl    %eax, %eax
        jmp     .LBB0_3
.Ltmp4:
        .size   readdir, .Ltmp4-readdir
        .cfi_endproc


        .weak   readdir64
readdir64 = readdir
        .section        ".note.GNU-stack","",@progbits

readdir.c

#include <dirent.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <errno.h>
#include <stdlib.h>
#include <limits.h>
#include "__dirent.h"
#include "syscall.h"
#include "libc.h"
#include "compiler.h"

int __getdents(int, struct dirent *, size_t);

struct dirent *readdir(DIR *dir)
{
        struct dirent *de;

        if (dir->buf_pos >= dir->buf_end) {
                int len = __getdents(dir->fd, (void *)dir->buf, sizeof dir->buf);
                if (len <= 0) return 0;
                dir->buf_end = len;
                dir->buf_pos = 0;
        }
        de = (void *)(dir->buf + dir->buf_pos);
        dir->buf_pos += de->d_reclen;
        dir->tell = de->d_off;
        return de;
}

LFS64(readdir);

readdir.diff

--- readdir.s   2012-07-03 15:25:01.324857380 +0000
+++ readdir_o.s 2012-07-03 15:25:28.108185315 +0000
@@ -14,20 +14,8 @@
        movq    %rdi, %rbx
        movl    16(%rbx), %eax
        cmpl    20(%rbx), %eax
-       jl      .LBB0_3
-# BB#1:
-       movl    (%rbx), %edi
-       leaq    32(%rbx), %rsi
-       movl    $2048, %edx             # imm = 0x800
-       callq   __getdents
-       movl    %eax, %ecx
-       xorl    %eax, %eax
-       testl   %ecx, %ecx
-       jle     .LBB0_4
-# BB#2:
-       movl    %ecx, 20(%rbx)
-       movl    $0, 16(%rbx)
-       xorl    %eax, %eax
+       jge     .LBB0_1
+       .align  16, 0x90
 .LBB0_3:
        movslq  %eax, %rax
        movzwl  48(%rbx,%rax), %ecx
@@ -37,9 +25,24 @@
        movq    40(%rbx,%rax), %rcx
        movq    %rcx, 8(%rbx)
        leaq    32(%rbx,%rax), %rax
+       .align  16, 0x90
 .LBB0_4:
        popq    %rbx
        ret
+.LBB0_1:
+       movl    (%rbx), %edi
+       leaq    32(%rbx), %rsi
+       movl    $2048, %edx             # imm = 0x800
+       callq   __getdents
+       movl    %eax, %ecx
+       xorl    %eax, %eax
+       testl   %ecx, %ecx
+       jle     .LBB0_4
+# BB#2:
+       movl    %ecx, 20(%rbx)
+       movl    $0, 16(%rbx)
+       xorl    %eax, %eax
+       jmp     .LBB0_3
 .Ltmp4:
        .size   readdir, .Ltmp4-readdir
        .cfi_endproc

readdir_o.c

#include <dirent.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <errno.h>
#include <stdlib.h>
#include <limits.h>
#include "__dirent.h"
#include "syscall.h"
#include "libc.h"
#include "compiler.h"

int __getdents(int, struct dirent *, size_t);

struct dirent *readdir(DIR *dir)
{
        struct dirent *de;

        if (unlikely(dir->buf_pos >= dir->buf_end)) {
                int len = __getdents(dir->fd, (void *)dir->buf, sizeof dir->buf);
                if (len <= 0) return 0;
                dir->buf_end = len;
                dir->buf_pos = 0;
        }
        de = (void *)(dir->buf + dir->buf_pos);
        dir->buf_pos += de->d_reclen;
        dir->tell = de->d_off;
        return de;
}

LFS64(readdir);