Re: PATCH: Re: Inefficient ia64 system call implementation in glibc

H. J. Lu
2003-09-25T04:34:55Z

On Wed, Sep 24, 2003 at 02:12:38PM -0700, Jim Wilson wrote:
> On Wed, 2003-09-24 at 11:56, H. J. Lu wrote:
> > I don't think it will be the problem. Compiler will do
> > addl outN = constant, r0
> > to pass a constant to the function, regardless what the type is. Am I
> > correct?
>
> No.
>
> The compiler will emit RTL like this
> (set (reg:SI outN) (const_int constant))
> which will translate to a
> addl outN = constant, r0
> instruction.
>
> However, if you are optimizing, then all we are guaranteed is that a
> value equivalent to an SImode constant will end up in the register. If
> you have something like
> if (i = 0)
> sub (0);
> and i has type int, and i happens to be already in the right register
> for the first argument to sub, then the compiler will optimize away the
> load of zero as redundant. The if statement uses cmp4 which only looks
> at the low order 4 bytes of i, and hence any value could be in the upper
> 4 bytes. This is OK per the ABI, which says that only the low 4 bytes
> of an integer argument are valid.
>

My patch only applies to LOAD_ARGS_##nr in

#define INTERNAL_SYSCALL(name, err, nr, args...) \
({ \
register long _r8 asm ("r8"); \
register long _r10 asm ("r10"); \
register long _r15 asm ("r15") = __NR_##name; \
long _retval; \
LOAD_ARGS_##nr (args); \
__asm __volatile (BREAK_INSN (__BREAK_SYSCALL) \
: "=r" (_r8), "=r" (_r10), "=r" (_r15) \
ASM_OUTARGS_##nr \
: "2" (_r15) ASM_ARGS_##nr \
: "memory" ASM_CLOBBERS_##nr); \
_retval = _r8; \
err = _r10; \
_retval; })

I don't think it is an issue here. The current one is

#define LOAD_ARGS_1(out0) \
register long _out0 asm ("out0") = (long) (out0); \
LOAD_ARGS_0 ()

I don't believe it is any better than

#define LOAD_ARGS_1(out0) \
register __typeof ((out0) + 0) _out0 asm ("out0") = (out0); \

as far as function prototype is concerned. If there is a mismatch,
long can have problems too.

H.J.