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Posting-Version: version B 2.10.1 6/24/83; site decwrl.UUCP
Path: utzoo!linus!philabs!cmcl2!floyd!harpo!decvax!decwrl!Jeff
From: Jeff@decwrl.UUCP
Newsgroups: net.bugs.4bsd
Subject: 4.2 (and 4.1) Vax pcc generates bad code for real comparisons
Message-ID: <6728@decwrl.UUCP>
Date: Tue, 3-Apr-84 05:29:28 EST
Article-I.D.: decwrl.6728
Posted: Tue Apr  3 05:29:28 1984
Date-Received: Thu, 5-Apr-84 01:07:06 EST
Organization: DEC Western Research Lab, Los Altos, CA
Lines: 95

Description:
	When pcc (the C compiler) generates code to compare a float
	and a double, it first converts the float to a double but
	doesn't realize that this takes two registers, not one.
	
	If more than one temporary register is in use while evaluating
	such a comparision, one of the register may be trashed.
	
	This bug applies to 4.1BSD and probably all earlier Vax pcc
	versions.
Repeat-By:
	compile this C program:
	
	double	dd[] =	{ 0.0, 2.0 };
	float	ff[] =	{ 0.0, 1.0 };
	int i = 1;

	main(){
		if( ff[i] >= dd[i] ) printf( "wrong\n" );
	}

	If you run it, it will print "wrong" because the 
	code that is generated (cf. cc -S) for the comparison
	is:

	movl	_i,r0
	movl	_i,r1
	cvtfd	_ff[r0],r0	# trashes r1
	cmpd	r0,_dd[r1]	# index is random
	jlss	L19

Fix:
	The fix given here may be suboptimal, but it seems to give
	correct code.  (I can't remember where I got the fix from;
	it's not mine.)  It tells pcc to use 2 stack longwords as
	a temporary instead of one register.
	
	On 4.1BSD, the file is /usr/src/cmd/pcc/table.c; it's identical
	to the 4.2 file.
	
	*** table.c.bad	Wed Dec 15 13:25:17 1982
	--- table.c	Mon Apr  2 16:05:08 1984
	***************
	*** 1,4
	  static char *sccsid ="@(#)table.c	1.1 (Berkeley) 12/15/82";
	  # include "mfile2"

	  # define WPTR TPTRTO|TINT|TLONG|TFLOAT|TDOUBLE|TPOINT|TUNSIGNED|TULONG

	--- 1,9 -----
	  static char *sccsid ="@(#)table.c	1.1 (Berkeley) 12/15/82";
	+ /*
	+  * 2 April 1984	Jeff Mogul	Stanford
	+  *	Re-installed fix to prevent compare of indexed float and
	+  *	indexed double from clobbering the index register.
	+  */
	  # include "mfile2"

	  # define WPTR TPTRTO|TINT|TLONG|TFLOAT|TDOUBLE|TPOINT|TUNSIGNED|TULONG
	***************
	*** 228,234
	  OPLOG,	FORCC,
		SAREG|AWD,	TDOUBLE,
		SAREG|AWD,	TFLOAT,
	! 		NAREG|NASR,	RESCC,
			"	cvtfd	AR,A1\n	cmpd	AL,A1\nZP",

	  OPLOG,	FORCC,

	--- 233,239 -----
	  OPLOG,	FORCC,
		SAREG|AWD,	TDOUBLE,
		SAREG|AWD,	TFLOAT,
	! 		2*NTEMP,	RESCC,
			"	cvtfd	AR,A1\n	cmpd	AL,A1\nZP",

	  OPLOG,	FORCC,
	***************
	*** 234,240
	  OPLOG,	FORCC,
		SAREG|AWD,	TFLOAT,
		SAREG|AWD,	TDOUBLE,
	! 		NAREG|NASL,	RESCC,
			"	cvtfd	AL,A1\n	cmpd	A1,AR\nZP",

	  OPLOG,	FORCC,

	--- 239,245 -----
	  OPLOG,	FORCC,
		SAREG|AWD,	TFLOAT,
		SAREG|AWD,	TDOUBLE,
	! 		2*NTEMP,	RESCC,
			"	cvtfd	AL,A1\n	cmpd	A1,AR\nZP",

	  OPLOG,	FORCC,