gcc 3.4.0 20040121 / ia32 / read-write constraint does not allow a register

[Etienne Lorrain <etienne_lorrain at yahoo dot fr>]

  Hello,

  While testing my current project with this GCC-3.4 snapshot:

[etienne@localhost gujin]$ ../toolchain-3.4/bin/gcc -v
Reading specs from
/home/etienne/projet/toolchain-3.4/bin/../lib/gcc/i686-pc-linux-gnu/3.4.0/specs
Configured with: ../configure --prefix=/home/etienne/projet/toolchain
--enable-languages=c
Thread model: posix
gcc version 3.4.0 20040121 (prerelease)

  I get a lot of warnings like:
gmem.h:818: warning: read-write constraint does not allow a register

  On asm("") like:
extern inline void fmemcpy (farptr dst, farptr src, unsigned short size)
  {
  extern char memory[]; /* memory barrier, char not aliased */

  asm (
"	pushl	%%es						\n"
"	pushl	%%esi						\n"
"	popw	%%si						\n"
"	popw	%%fs						\n"
"	pushl	%%edi						\n"
"	popw	%%di						\n"
"	popw	%%es						\n"
"	cld		# fmemcpy modify %3			\n"
"	rep movsb %%fs:(%%si),%%es:(%%di)	# no macro	\n"
"	nop							\n"
"	popl	%%es						\n"
	: "+S" (src), "+D" (dst), "+c" (size), "+m" (*memory)
	:
	: "cc"
	);
  }

  I do not know if the warning is bogus or I am no more allowed to
 write: "+S" (src), "+D" (dst), "+c" (size)

  I checked the doc of 3.3:

When the compiler fixes up the operands to satisfy the constraints, it needs
to know which operands are inputs to the instruction and which are outputs
from it. = identifies an output; + identifies an operand that is both input
and output; all other operands are assumed to be input only. 

  Can someone enlighten me?

  Thanks,
  Etienne.

  Note also that I still have calls to memcpy emitted even when
 -Os -march=i386 and -minline-all-stringops while copying relatively big
 structures by the equal sign (my inline function memcpy cannot
 expand), as discussed last month.



	

	
		
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