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List:       pcc-list
Subject:    Re: Problem with liveliness of hard registers
From:       Anders Magnusson <ragge () ludd ! ltu ! se>
Date:       2007-11-12 11:04:49
Message-ID: 47383351.2020502 () ludd ! ltu ! se
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Hi,

Gregory McGarry wrote:
> Revision 1.160 of pcc/mip/regs.c didn't exhibit this problem.  1.161 
> does.
>
> Here's what I noticed on powerpc for the following program:
>
> In main(), the call to val1() correctly handles the return values in 
> R3:R4.  While for the call to val2(), the compiler thinks the return 
> values are R5:R6.
>
> Is the problem that registers R3 and R4 are used as function arguments 
> to val2() and also used as outputs of val2()?  [Actually, I just added 
> an extra argument to val2() and the compiler thought the outputs were 
> in R7:R8, so I think this a valid conclusion.]  Is the liveliness 
> analysis getting confused that the registers changed inside val2()?
>
> I'll look more closely at the changes in 1.161.
What's causing the problem here is that rmove() isn't implemented.  The 
compiler moves
R3:R4 to R5:R6 by calling rmove after the call.  (there is a liveness 
problem also but
the compiler fixes that :-)

Also note that the concatenated registers do not need PERMREG/TEMPREG 
attributes
set, the attributes are already set on the individual regs and we do not 
need to save
the registers more than once, eh? :-)

-- Ragge

>
> long long
> val1()
> {
>         return (0x1234567890abcdefLL);
> }
>
> long long
> val2(long long v)
> {
>         return (v-1);
> }
>
> void
> main()
> {
>         printf("this: %llx\n", val1());
>         printf("this: %llx\n", val2(0x1234567890abcdefLL));
> }
>
>
>
>
>         bl _val1        ; call (no args, result in r3:r4) to 
> scon/sname (_val1)
> -    [ return values in r3:r4]
>         mr r5,r4        ; assign r3:r4 to r4:r5
>         mr r4,r3
>         lis r3,ha16(L20)
>         addi r3,r3,lo16(L20)
>         bl _printf      ; call (args, no result) to scon/sname (_printf)
> -    [ printf(R3,R4,R5) ]
>
>         lis r4,ha16(-1867788817)
>         addi r4,r4,lo16(-1867788817)
>         lis r3,ha16(305419896)
>         addi r3,r3,lo16(305419896)
>         bl _val2        ; call (args, result in r3:r4) to scon/sname 
> (_val2)
> -    [ return values in r3:r4]
>         stw r6,56(r1)   ; store 64-bit value
>         stw r5,60(r1)
> -    [ what??? ]
>         lwz r5,56(r1)   ; assign llong to reg
>         lwz r4,60(r1)
>         lis r3,ha16(L20)
>         addi r3,r3,lo16(L20)
>         bl _printf      ; call (args, no result) to scon/sname (_printf)
> -    [ printf(R3,R4,R5) ]
>

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