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Re: 64-bit on ia-32

On Tuesday, Aug 12, 2003, at 18:30 US/Eastern, Johan Rydberg wrote:


For a program I'm writing, I must use 64-bit datatypes on a IA-32
host.  Since performance is everything for this application, I'm
looking at the code that GCC generates; and I have found something
that I think could be done better.  Take the following example:

register unsigned long long v0 asm ("%esi");

union u
    unsigned int ww[2];
    unsigned long long ll;

extern int p1, p2;
#define P1 ((int) &p1)
#define P2 ((int) &p2)

static void
move1 (void)
  v0 = (((unsigned long long) P1 << 32) & 0xffffffff00000000ULL
        | ((unsigned long long) P2) & 0xffffffffULL) ;

For move1 I might be able to fix this to be about the same as move2 (and maybe better)
but this work will not get done for another month or two.

One of the problems with move1 right now is that GCC does not know how to combine these two rtl
(since this is a list about development of GCC I assume you know how to read the rtl's):
(set (reg:DI 58) (sign_extend:DI (reg/f:SI 59)))
(set (reg:DI 60) (ashift:DI (reg:DI 58) (const_int 32 [0x20])))
(set (reg:DI 60) (ashift:DI (reg:SI 58) (const_int 32 [0x20])))

Another issue is something called libcalls which produces weaker than what it should (there are several bugs against them).
I would file a bug for move1 so we know what the problem exists and can get to it.

Andrew Pinski

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