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From: mjy@sdti.UUCP (Michael J. Young)
Newsgroups: comp.sys.ibm.pc,comp.unix.xenix
Subject: Re: 386 unix (was Re: 386 demand paged virtual memory)
Message-ID: <129@sdti.UUCP>
Date: Fri, 25-Sep-87 12:24:34 EDT
Article-I.D.: sdti.129
Posted: Fri Sep 25 12:24:34 1987
Date-Received: Sun, 27-Sep-87 09:38:02 EDT
References: <125@snark.UUCP> <299@nuchat.UUCP> <358@netxcom.UUCP> <158@splut.UUCP> <380@micropen> <98@sdeggo.UUCP>
Reply-To: mjy@sdti.UUCP (0000-Michael J. Young)
Organization: Software Development Technologies, Sudbury MA
Lines: 66
Xref: mnetor comp.sys.ibm.pc:8319 comp.unix.xenix:837

In article <98@sdeggo.UUCP> dave@sdeggo.UUCP (David L. Smith) writes:
>In article <380@micropen>, dave@micropen (David F. Carlson) writes:
>> Are there any beta sites that can confirm or deny these rather reasonable
>> claims?  Has anyone *ever* had a demonstrable, verifiable compiler bug
>> with the Microport PCC-based compiler?

I don't know anything about the 386 compiler, but the following code breaks
the 286 compiler:

int *alloc();
int kl()
{
	int s;
	char *am;
	(am == 0) ?
		(am = (char *) alloc((long) s)):
		0;
}

Compiling the above function in large memory model causes an internal
compiler error : register allocation error.  The generated code (up until
the compiler aborts) is:

	.file	"t1.c"
	.data
	.text
	.def	kl; .val kl; .scl 2; .type 044; .endef
	.globl	kl
kl:
	enter	$.F1,$0
	test	-4(%bp)
	jne	.10000
	test	-6(%bp)
	jne	.10000
.10001:
	mov	-2(%bp),%ax
	cwd
	push	%dx
	push	%ax
	lcall	alloc
	add	$4,%sp
	mov	%ax,-6(%bp)
	mov	%dx,-4(%bp)
	jmp	.10002
.10000:
	xor	%ax,%ax
	xor	%dx,%dx
.10002:
	mov	%ax,%bx		; oops!
	mov	%bx,%ax

I'd be interested to hear if this problem is also present in the 386
compiler.  The conditional construct that causes wedges the compiler
is frequently generated by C++.  In fact, the code fragment I included
here was given to us by Bjarne Stroustrup as proof that C++ could not
easily be ported to a 286 machine that used the intel pcc-based compiler.
(I have heard that other non-pcc-based compilers, such as Metaware's
High-C, do not have this problem).

Anyone with a beta copy of System V/386 care to try it and see if it
works?
-- 
Mike Young - Software Development Technologies, Inc., Sudbury MA 01776
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