Lwan template interpreter

gistfile1.txt

New                                    Old      
                                       
movsx  esi,BYTE PTR [r14+0x8]          movsx  esi,BYTE PTR [r13+0x8]      
mov    rdi,r12                         mov    rdi,rbp      
add    rbx,0x1                         add    r13,0x18      
call   0x412fd0 <strbuf_append_char>   call   0x413ed0 <strbuf_append_char>      
mov    rax,QWORD PTR [r15+rbx*8]       mov    eax,DWORD PTR [r13+0x0]      
jmp    QWORD PTR [rax*8+0x416440]      mov    rax,QWORD PTR [rax*8+0x4166a0]      
                                       jmp    rax


C:                                     C:
   pc++;                                  chunk++;
   goto *dispatch_table[ops[pc]];         goto *dispatch_table[chunk->action];
                                           

`struct chunk` is 0x18 bytes. `ops` is an array of all the `action` fields from a `struct chunk` array,
tightly packed together. Code is pretty much equivalent, except that GCC had to load the next address
to `rax` and then jump there; it couldn't fuse the read with the indirect jump. Why?

@ricbit: I didn't measure; I've no idea if there's any difference, but I was puzzled anyway. The version on the left is 8 bytes shorter than the version on the right. Architecture is x86-64; my machine is a Sandy Bridge Core i7.

The C code for this snippet is here.