PATCH ARM: fix output_call_mem when the address references LR.

[Richard Earnshaw <rearnsha at arm dot com>]

I came across this last night on an application I built with gcc-3.3

The code sequence for calling via a function pointer on ARM is normally

	mov	lr, pc
	ldr	pc, [address]

This works fine unless ADDRESS references the link register (LR).  To work 
around this we copy LR into IP if it is referenced (since IP will be 
clobbered by the call).  Unfortunately, if IP was also live (ie part of 
the address) then we get corrupt code, something like

	mov	ip, lr
	mov	lr, pc
	ldr	pc, [ip, ip]	// Ooops

This patch fixes things so that we do the load in the first instruction, 
thus guaranteeing that we don't earlyclobber anything...

	ldr	ip, [lr, ip]
	mov	lr, pc
	mov	pc, ip		// Kills ip

Checking back through some archives I find that I added the original code 
for this in October 93!  It's amazing how long some bugs can lie dormant.

2003-06-13  Richard Earnshaw  <rearnsha@arm.com>

	* arm.c (output_call_mem): If the address references the link-register
	use an instruction sequence that avoids early-clobbering IP.
	(eliminate_lr2ip): Delete.

Attachment: call-mem.patch
Description: call-mem.patch