lint: extract code for determining possible precedence confusion

The function check_precedence_confusion was pretty long, and right in
the middle of that function was the complicated part of determining
which of the operand combinations are confusing and which aren't.

Extract this part into a separate function to document on which
information this decision is based.  This makes it easier to understand
the code since there are fewer local variables around.

As a left-over from a previous commit, rop and rparn don't need to be
initialized twice, now that the assertion for a binary operator is in
place.

Remove the large and useless switch statement over all operator types.
This list was completely unsorted, for no apparent reason.  To see the
list of operators, better look them up in ops.def, there was no need to
have this list duplicated here.

usr.bin/xlint/lint1/tree.c

@@ -1,4 +1,4 @@
-/*	$NetBSD: tree.c,v 1.133 2021/01/04 23:58:19 rillig Exp $	*/
+/*	$NetBSD: tree.c,v 1.134 2021/01/05 00:17:21 rillig Exp $	*/
 
 /*
  * Copyright (c) 1994, 1995 Jochen Pohl
@@ -37,7 +37,7 @@
 
 #include <sys/cdefs.h>
 #if defined(__RCSID) && !defined(lint)
-__RCSID("$NetBSD: tree.c,v 1.133 2021/01/04 23:58:19 rillig Exp $");
+__RCSID("$NetBSD: tree.c,v 1.134 2021/01/05 00:17:21 rillig Exp $");
 #endif
 
 #include <float.h>
@@ -3977,6 +3977,46 @@ cat_strings(strg_t *strg1, strg_t *strg2)
 	return strg1;
 }
 
+static bool
+is_confusing_precedence(op_t op, op_t lop, bool lparen, op_t rop, bool rparen)
+{
+
+	if (op == SHL || op == SHR) {
+		if (!lparen && (lop == PLUS || lop == MINUS)) {
+			return true;
+		} else if (!rparen && (rop == PLUS || rop == MINUS)) {
+			return true;
+		}
+		return false;
+	}
+
+	if (op == LOGOR) {
+		if (!lparen && lop == LOGAND) {
+			return true;
+		} else if (!rparen && rop == LOGAND) {
+			return true;
+		}
+		return false;
+	}
+
+	lint_assert(op == AND || op == XOR || op == OR);
+	if (!lparen && lop != op) {
+		if (lop == PLUS || lop == MINUS) {
+			return true;
+		} else if (lop == AND || lop == XOR) {
+			return true;
+		}
+	}
+	if (!rparen && rop != op) {
+		if (rop == PLUS || rop == MINUS) {
+			return true;
+		} else if (rop == AND || rop == XOR) {
+			return true;
+		}
+	}
+	return false;
+}
+
 /*
  * Print a warning if the given node has operands which should be
  * parenthesized.
@@ -3988,10 +4028,9 @@ static void
 check_precedence_confusion(tnode_t *tn)
 {
 	tnode_t	*ln, *rn;
-	op_t	lop, rop = NOOP;
+	op_t	lop, rop;
-	int	lparn, rparn = 0;
+	bool	lparn, rparn;
 	mod_t	*mp;
-	int	dowarn;
 
 	if (!hflag)
 		return;
@@ -4001,117 +4040,20 @@ check_precedence_confusion(tnode_t *tn)
 
 	dprint_node(tn);
 
-	lparn = 0;
+	lparn = false;
 	for (ln = tn->tn_left; ln->tn_op == CVT; ln = ln->tn_left)
 		lparn |= ln->tn_parenthesized;
 	lparn |= ln->tn_parenthesized;
 	lop = ln->tn_op;
 
-	rparn = 0;
+	rparn = false;
 	for (rn = tn->tn_right; rn->tn_op == CVT; rn = rn->tn_left)
 		rparn |= rn->tn_parenthesized;
 	rparn |= rn->tn_parenthesized;
 	rop = rn->tn_op;
 
-	dowarn = 0;
+	if (is_confusing_precedence(tn->tn_op, lop, lparn, rop, rparn)) {
-
-	switch (tn->tn_op) {
-	case SHL:
-	case SHR:
-		if (!lparn && (lop == PLUS || lop == MINUS)) {
-			dowarn = 1;
-		} else if (!rparn && (rop == PLUS || rop == MINUS)) {
-			dowarn = 1;
-		}
-		break;
-	case LOGOR:
-		if (!lparn && lop == LOGAND) {
-			dowarn = 1;
-		} else if (!rparn && rop == LOGAND) {
-			dowarn = 1;
-		}
-		break;
-	case AND:
-	case XOR:
-	case OR:
-		if (!lparn && lop != tn->tn_op) {
-			if (lop == PLUS || lop == MINUS) {
-				dowarn = 1;
-			} else if (lop == AND || lop == XOR) {
-				dowarn = 1;
-			}
-		}
-		if (!dowarn && !rparn && rop != tn->tn_op) {
-			if (rop == PLUS || rop == MINUS) {
-				dowarn = 1;
-			} else if (rop == AND || rop == XOR) {
-				dowarn = 1;
-			}
-		}
-		break;
-		/* LINTED206: (enumeration values not handled in switch) */
-	case DECAFT:
-	case XORASS:
-	case SHLASS:
-	case NOOP:
-	case ARROW:
-	case ORASS:
-	case POINT:
-	case NAME:
-	case NOT:
-	case COMPL:
-	case CON:
-	case INC:
-	case STRING:
-	case DEC:
-	case INCBEF:
-	case DECBEF:
-	case INCAFT:
-	case FSEL:
-	case CALL:
-	case COMMA:
-	case CVT:
-	case ICALL:
-	case LOAD:
-	case PUSH:
-	case RETURN:
-	case INIT:
-	case CASE:
-	case FARG:
-	case SUBASS:
-	case ADDASS:
-	case MODASS:
-	case DIVASS:
-	case MULASS:
-	case ASSIGN:
-	case COLON:
-	case QUEST:
-	case LOGAND:
-	case NE:
-	case EQ:
-	case GE:
-	case GT:
-	case LE:
-	case LT:
-	case MINUS:
-	case PLUS:
-	case MOD:
-	case DIV:
-	case MULT:
-	case AMPER:
-	case STAR:
-	case UMINUS:
-	case SHRASS:
-	case UPLUS:
-	case ANDASS:
-	case REAL:
-	case IMAG:
-		break;
-	}
-
-	if (dowarn) {
 		/* precedence confusion possible: parenthesize! */
 		warning(169);
 	}
-
 }