Cannot understand the reloading code

[wuxi]

Hi,

I am working on Itanium and gcc4.1.1. My work is mainly do 
instrumentations to enable efficient taint tracking (using NaT bit on 
IA-64 to represent tainted data.) on IA-64.(recently i am porting my 
code to gcc4.3.2, but that has not been accomplished, because i should 
also port my modified glibc to a compatible version with gcc4.3.2).

Some modifications recently is, I move some of my instrumentations up 
before life analysis, and I allocate pseudo registers to do the 
instrumentation. From the INSN list after my pass, it seems that all 
instrumentation is done well. And for each sensitive INSN I care, I 
allocate enough pseudo registers to do instrumentation, by calling 
gen_reg_rtx to allocate new pseudos. For example, the following is a 
sequence for instrumenting a cmp instruction IA-64:

=========================================================
the INSN I want to instrument is :
(insn 21 46 47 0 (set (reg:BI 343)
        (eq:BI (reg/v:SI 339 [ zipfile ])
            (const_int -1 [0xffffffffffffffff]))) 233 {*cmpsi_normal} (nil)
    (nil))
=========================================================

=========================================================
after instrumentation, it becomes the following INSN list:

r346 is the pseudo register allocated for instrumentation.

//this instruction is the "tnat" instruction I added in ia64.md, it test 
the NaT bit of r399
(insn 43 19 44 0 (set (reg:BI 346)
        (unspec:BI [
                (reg:DI 339)
            ] 32)) -1 (nil)
    (nil))

// st8.spill r399 into [r0] (i allocated memory for NULL), the goal here 
is to clear NaT bit
(insn 44 43 46 0 (cond_exec (ne:BI (reg:BI 346)
            (const_int 0 [0x0]))
        (parallel [
                (set (mem:DI (reg/f:DI 0 r0) [0 S8 A64])
                    (unspec:DI [
                            (reg:DI 339)
                            (const_int 0 [0x0])
                        ] 10))
                (clobber (reg:DI 330 ar.unat))
            ])) -1 (nil)
    (nil))

// load it again, now r339 won't have NaT bit
(insn 46 44 21 0 (cond_exec (ne:BI (reg:BI 346)
            (const_int 0 [0x0]))
        (set (reg:DI 339)
            (mem:DI (reg/f:DI 0 r0) [0 S8 A64]))) -1 (nil)
    (nil))

// do real cmp
(insn 21 46 47 0 (set (reg:BI 343)
        (eq:BI (reg/v:SI 339 [ zipfile ])
            (const_int -1 [0xffffffffffffffff]))) 233 {*cmpsi_normal} (nil)
    (nil))

// restore the NaT bit for r339
(insn 47 21 22 0 (cond_exec (ne:BI (reg:BI 346)
            (const_int 0 [0x0]))
        (set (reg:DI 339)
            (plus:DI (reg:DI 4 r4)
                (reg:DI 339)))) -1 (nil)
    (nil))

=========================================================

Now the problem comes, when global allocation completes, there is still 
pseudo register. In the dump file .greg, I found the following:

Reloads for insn # 43
Reload 0: reload_in (DI) = (reg:DI 339)
    GR_REGS, RELOAD_FOR_INPUT (opnum = 1)
    reload_in_reg: (reg:DI 339)
    reload_reg_rtx: (reg:DI 14 r14)

the spilling info says:
Spilling for insn 43.
Using reg 14 for reload 0

This is correct, and I found the INSN list above, all r339 have been 
replaced by r14.

But there is an extra INSN inserted, that is:
(insn 57 7 43 0 (set (reg:DI 14 r14)
        (reg:DI 339)) 5 {*movdi_internal} (nil)
    (nil))

how can r339 appears again? this is spilling? I am confused by this.

So any help, I want some advices to help me where I should dig into to 
resolve this problem. I have been reading code in reload1.c, 
particularly inc_for_reload, I observe it will generate emit_move_insn 
for some purpose, but I don't quite understand...

Any help is truly appreciated :-)

Thanks!

yours sincerely

Andrew