Re: [v3 RFC] PATCH to memory asm ops in atomicity.h

[Jason Merrill <jason at redhat dot com>]

On Thu, 18 Dec 2003 11:58:32 -0800, Richard Henderson <rth@redhat.com> wrote:

> On Thu, Dec 18, 2003 at 12:14:52PM -0500, Jason Merrill wrote:
>> Are you also agreeing that "+m" is converted into a matching restraint?
>
> Yes, it is.

OK.  Doc patch follows.  Would you suggest that expand_asm_operands warn if
we see either an in/out operand or a matching restraint that doesn't allow
a register?

*** extend.texi.~1~	2003-11-26 10:22:46.000000000 -0500
--- extend.texi	2003-12-18 15:35:21.000000000 -0500
*************** The ordinary output operands must be wri
*** 3908,3925 ****
  the values in these operands before the instruction are dead and need
  not be generated.  Extended asm supports input-output or read-write
  operands.  Use the constraint character @samp{+} to indicate such an
! operand and list it with the output operands.
! 
! When the constraints for the read-write operand (or the operand in which
! only some of the bits are to be changed) allows a register, you may, as
! an alternative, logically split its function into two separate operands,
! one input operand and one write-only output operand.  The connection
! between them is expressed by constraints which say they need to be in
! the same location when the instruction executes.  You can use the same C
! expression for both operands, or different expressions.  For example,
! here we write the (fictitious) @samp{combine} instruction with
! @code{bar} as its read-only source operand and @code{foo} as its
! read-write destination:
  
  @example
  asm ("combine %2,%0" : "=r" (foo) : "0" (foo), "g" (bar));
--- 3908,3926 ----
  the values in these operands before the instruction are dead and need
  not be generated.  Extended asm supports input-output or read-write
  operands.  Use the constraint character @samp{+} to indicate such an
! operand and list it with the output operands.  You should only use
! read-write operands when the constraints for the operand (or the
! operand in which only some of the bits are to be changed) allow a
! register.
! 
! You may, as an alternative, logically split its function into two
! separate operands, one input operand and one write-only output
! operand.  The connection between them is expressed by constraints
! which say they need to be in the same location when the instruction
! executes.  You can use the same C expression for both operands, or
! different expressions.  For example, here we write the (fictitious)
! @samp{combine} instruction with @code{bar} as its read-only source
! operand and @code{foo} as its read-write destination:
  
  @example
  asm ("combine %2,%0" : "=r" (foo) : "0" (foo), "g" (bar));