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How are case statements laid out?

From: Peter Barada <pbarada at mail dot wm dot sps dot mot dot com>
Cc: gcc at gcc dot gnu dot org
Date: Mon, 3 Dec 2001 12:51:59 -0500
Subject: How are case statements laid out?
References: <Pine.BSF.4.42.0112031524050.66463-100000@naos.dbai.tuwien.ac.at>


I noticed that the case statement for 68k/Coldfire generates code
along the lines of:

	.set .LI87,.+2
	move.w .L87-.LI87.b(%pc,%d0.l*2),%d0
	ext.l %d0
	jmp %pc@(2,%d0:l)
	.align 2
	.swbeg &10
.L87:
	.word .L64-.L87
	.word .L65-.L87
	.word .L64-.L87

This allows a displacement between .L87 and the start of the case body
to be up to 32767 bytes away(forward or backward since %d0 is
*sign-extended*).  If the code is changed to: 

	.set .LI87,.+2
	moveq.l #0,%d0
	move.w .L87-.LI87.b(%pc,%d0.l*2),%d0
	jmp %pc@(2,%d0:l)
	.align 2
	.swbeg &10
.L87:
	.word .L64-.L87
	.word .L65-.L87
	.word .L64-.L87


Then the displacement can go *forward* up to 65535 bytes away(since
%d0 is *zero-extended*).  My question is whether or not the compiler
*always* places the switch selector before the case body?

-- 
Peter Barada                                   Peter.Barada@motorola.com
Wizard                                         781-852-2768 (direct)
WaveMark Solutions(wholly owned by Motorola)   781-270-0193 (fax)

Follow-Ups:
- Re: How are case statements laid out?
  - From: Richard Henderson

References:
- Re: copyright assignment papers
  - From: Gerald Pfeifer

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