Subject: addendum to last C compiler patch
Index:	lib/ccom/c10.c 2.11BSD

Description:
	The previous update to the C compiler generated better code
	for the u_char -> char case but broke the case where the u_char
	was being moved to a register.

Repeat-By:
	compile the test program:

	unsigned char	x; main() {register int y; y = x;}

	note that a "movb _x,r4" is generated instead of "clr r0;bisb _x,r0;
	mov r0,r4".

Fix:
	Apply the following patch (after installing the previous one) and
	remake 'c1'.
--------------------------------------------------------------------------
*** c10.c.old	Sat Oct  5 16:41:38 1991
--- c10.c	Wed Oct  9 17:02:52 1991
***************
*** 508,513 ****
--- 508,531 ----
  	 && (tree->t.tr1->t.type==CHAR || tree->t.tr1->t.type==UNCHAR)
  	 && tree->t.tr2->t.type!=CHAR && tree->t.tr2->t.type!=UNCHAR)
  		tree->t.tr2 = tnode(LOAD, tree->t.tr2->t.type, tree->t.tr2, TNULL);
+ 	/*
+ 	 * Another peculiarity of the PDP11 table manifested itself when
+ 	 * amplifying the move3: table.  The same case which optimizes
+ 	 * u_char to char moves is used to move a u_char to a register. This
+ 	 * is wrong, leading to sign extension.  Rather than lose the ability
+ 	 * to generate better code when moving a u_char to a char, a check 
+ 	 * is made here to prevent sign extension.
+ 	 *
+ 	 * If the opcode is assign, the destination is a register and the
+ 	 * source is u_char then do a conversion.
+ 	 *
+ 	 * u_char handling in the compiler is a bit awkward, it would be nice
+ 	 * if %aub in the tables had a more unique meaning.
+ 	*/
+ 	if (tree->t.tr2 && tree->t.tr1->t.op == NAME
+ 	 && tree->t.tr1->n.class == REG && tree->t.op == ASSIGN
+ 	 && tree->t.tr2->t.type == UNCHAR)
+ 		tree->t.tr2 = tnode(LOAD, UNSIGN, tree->t.tr2, TNULL);
  	if (table==cregtab)
  		table = regtab;
  	/*