Re: __builtin_constant_p and inline assembly constraints

[Simon Kagstrom <simon dot kagstrom at bth dot se>]

At Tue, 22 Aug 2006 14:44:44 +0100,
Andrew Haley wrote:
> Simon Kagstrom writes:
>  > I'm trying to dyanmically generate different bitpatterns using inline
>  > assembly depeding on a value is constant or not. I'm using it to issue
>  > system calls (see http://spel.bth.se/index.php/Cibyl) and avoid
>  > clobbering registers with constant values. What I'm trying to achieve
>  > is this:
>  > 
>  > 	move    a0,v0	# Normal MIPS instruction
>  > 	0000fffd 	# Argument, is a constant
>  > 	00000020 	# Constant 32
>  > 	ffff0001 	# System call number 1
> [...]
> Trying something simpler, 
> 
> #include <stdio.h>
> int main() {
>   printf("%d\n", __builtin_constant_p("Hello!"));
> }
> 
> returns 1.

Hmm... I tried this example and it seems that this might be a problem
with my version of GCC for MIPS. It works fine with Debian/testing GCC
3.3.6, 3.4.6 and 4.1.2 but the MIPS cross compiler (3.4.3) doesn't
work. The flags I use to compile are

  -Wall -mips1 -fno-delayed-branch -Os -fno-pic -mno-abicalls

> Can you try expanding your example with gcc -E, and paste the result
> here so I can try it?  Then we'll have a test case we can use.

I've attached it below.

The code is slightly changed but the result is the same. I now do

#define __emit_parameter(x) \
  if (__builtin_constant_p(x)) { \
    __asm__ volatile ( \
    ".long  0xfffd0000\n" \
    ".long  %0\n" \
    : \
    : "i,!r"(x) \
    ); \
  } \
  else { \
    __asm__ volatile ( \
    ".short  0xfffe\n" \
    ".short  %0\n" \
    : \
    : "r"(x) \
    ); \
  }

#define _syscall1(type,name,atype,a) \
type name(atype a) \
{ \
	register unsigned long __v0 asm("$2"); \
	\
	__asm__ volatile (".set  push\n.set  noreorder\n"); \
        __emit_parameter(a); \
	...

but the result is the same. Thanks for looking into this.

// Simon

Attachment: main.out
Description: Binary data