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Why does gcc produce an unnecessary `nop' instruction?
- From: "PRC" <panruochen at gmail dot com>
- To: "gcc-help" <gcc-help at gcc dot gnu dot org>
- Date: Fri, 25 Jan 2008 12:22:21 +0800
- Subject: Why does gcc produce an unnecessary `nop' instruction?
Here is my code:
-----------------------------------------------
void loadicon(void)
{
static unsigned char icon_buf[] = {
#include "icon1.dat"
#include "icon2.dat"
};
SetBufAddr(icon_buf);
}
-----------------------------------------------
And I compile it with sde-gcc ( Version 6.06 ) with options -O2 -mips32r2
The assembly code produced by gcc is:
-----------------------------------------------
800650b0 <loadicon>:
800650b0: 3c048006 lui a0,0x8006
800650b4: 0801964b j 8006592c <SetBufAddr>
800650b8: 24846128 addiu a0,a0,24872
800650bc: 00000000 nop
-----------------------------------------------
The `nop' instruction seems useless at all here.
And I try another compiler mips-elf-gcc, and get
-----------------------------------------------
800650c0 <loadicon>:
800650c0: 3c048006 lui a0,0x8006
800650c4: 0801963b j 800658ec <SetBufAddr>
800650c8: 248460e8 addiu a0,a0,24808
-----------------------------------------------
There is no any more `nop'.
The gcc core of sde-gcc is 3.4.4, newer than that of mips-elf-gcc which is 3.4.0.
Based on what reasons the new gcc code produces an `nop' ?