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Path: utzoo!mnetor!seismo!think!sam
From: sam@think.uucp (Sam Kendall)
Newsgroups: comp.bugs.4bsd,comp.bugs.sys5,comp.lang.c,comp.lang.c++
Subject: C compiler bug on 4.3BSD, Ultrix, Sun 3.2, System V.2
Message-ID: <2488@think.UUCP>
Date: Tue, 17-Mar-87 16:18:26 EST
Article-I.D.: think.2488
Posted: Tue Mar 17 16:18:26 1987
Date-Received: Thu, 19-Mar-87 01:15:01 EST
Sender: news@think.UUCP
Lines: 65
Xref: mnetor comp.bugs.4bsd:230 comp.bugs.sys5:85 comp.lang.c:1273 comp.lang.c++:179

Index:	/usr/src/lib/mip/trees.c 4.3BSD +FIX

Description:
	The C compiler on 4.3BSD, Ultrix, Sun 3.2 and System V.2 (tested
	on 3B20 only) allows one to cast a structure or a double into a
	pointer.  Usually this happens without complaint, and the
	generated code takes the first word of the structure or double
	to be the value of the pointer; for some code you will get
	second pass complaints (on 4.3BSD VAX, "compiler error: no table
	entry for op REG"; on Sun, "expression causes compiler loop: try
	simplifying").  This bug is NOT present in the UniSoft V7
	compiler, oddly  enough.

	Note for C++ users: C++ releases 1.1 and 1.2 can generate
	erroneous code that passes cc without error because of this bug,
	so I suggest you install this fix.  (We will post separately
	about this C++ bug.)

	We include the fix for the 4.3BSD C compiler only.  The fixes
	for the other compilers are probably identical.

Repeat-By:
	Compile this program with "cc -S":

		main(){
			struct { int i; } s;
			f((char *) s);
		}

	Notice the lack of complaint.  Inspect the assembly code if you
	wish.  Now replace `(char *) s' with `(char *)(0, s)', and you
	will get the second pass complaint.
	
Fix:
	After you make this change, recompile all the binaries made from
	the portable C compiler sources (except that Fortran doesn't
	need to be recompiled).  On BSD	systems, these binaries are
	ccom, sccom, and lint.  Don't forget lint!

*** trees.c~	Tue Mar  3 12:08:05 1987
--- trees.c	Tue Mar  3 12:29:30 1987
***************
*** 1416,1422 ****
  		else if( mt2 == 0 &&
  		        ( p->in.right->in.op == CALL ||
  			  p->in.right->in.op == UNARY CALL)) break;
! 		else if( mt1 & MPTR ) return( LVAL+PTMATCH+PUN );
  		else if( mt12 & MPTI ) return( TYPL+LVAL+TYMATCH+PUN );
  		break;
  
--- 1416,1426 ----
  		else if( mt2 == 0 &&
  		        ( p->in.right->in.op == CALL ||
  			  p->in.right->in.op == UNARY CALL)) break;
! 		/*
! 		 * Test of mt2 below added by sam@think.com 3/3/87.  Fixes bug
! 		 * that struct, double could be cast to ptr without complaint.
! 		 */
! 		else if( (mt1&MPTR) && (mt2&MPTI) ) return( LVAL+PTMATCH+PUN );
  		else if( mt12 & MPTI ) return( TYPL+LVAL+TYMATCH+PUN );
  		break;
  
---
Sam Kendall			sam@Think.COM
Thinking Machines Corp.		{seismo,ihnp4}!think!sam