The attached patch enforces the operand constraints on the Arm SWP 
instruction.  The address register may not overlap the other registers.

Tested with cross to arm-none-eabi.
Ok?

Paul

2005-09-02  Paul Brook  <paul@codesourcery.com>

gas/
	* config/tc-arm.c (do_rn_rd): Enforce SWP operand constraints.
gas/testsuite/
	* gas/arm/arm3-bad.s: New test.
	* gas/arm/arm3-bad.d: New test.
	* gas/arm/arm3.s: Avoid illegal instructions.
	* gas/arm/arm3.d: Ditto.