lint: warn about unreachable case labels for '&&'
See octeon_gmxreg.h 1.2 from 2020-06-18 for an example, where RXN_RX_INBND_SPEED was cleaned up without adjusting the corresponding code in octeon_gmx.c.
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rillig
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40cc624231
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c910954897
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@ -1,4 +1,4 @@
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# $NetBSD: Makefile,v 1.56 2021/05/14 21:14:55 rillig Exp $
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# $NetBSD: Makefile,v 1.57 2021/05/15 19:12:14 rillig Exp $
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NOMAN= # defined
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MAX_MESSAGE= 343 # see lint1/err.c
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@ -104,6 +104,7 @@ FILES+= emit.c
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FILES+= emit.exp
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FILES+= emit.ln
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FILES+= expr_range.c
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FILES+= expr_range.exp
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FILES+= feat_stacktrace.c
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FILES+= feat_stacktrace.exp
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FILES+= gcc_attribute.c
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@ -1,37 +1,43 @@
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/* $NetBSD: expr_range.c,v 1.1 2021/05/14 21:14:55 rillig Exp $ */
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/* $NetBSD: expr_range.c,v 1.2 2021/05/15 19:12:14 rillig Exp $ */
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# 3 "expr_range.c"
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/*
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* Test whether lint can detect switch branches that are impossible to reach.
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* As of 2021-05-14, it cannot. To do this, it would need to keep track of
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* the possible values of each variable or expression. To do this reliably,
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* it would also need accurate control flow analysis, which as of 2021-05-14
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* works only for functions without 'goto'.
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* In a switch statement that has (expr & constant) as the controlling
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* expression, complain if one of the case branches is unreachable because
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* the case label does can never match the controlling expression.
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*
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* GCC 10 does not complain the unreachable branch. It knows that the branch
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* is unreachable though since it doesn't generate any code for it. GCC once
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* had the option -Wunreachable-code, but that option was made a no-op in
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* 2011.
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* GCC 10 does not complain about the unreachable branch. It knows that the
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* branch is unreachable though since it doesn't generate any code for it.
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* GCC once had the option -Wunreachable-code, but that option was made a
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* no-op in 2011.
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*
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* Clang 10 does not complain about this either, and just like GCC it doesn't
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* generate any code for this branch. The code for tracking an expression's
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* possible values may be related to RangeConstraintManager, just guessing.
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*
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* There should be at least one static analysis tool that warns about this.
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*/
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/* lint1-extra-flags: -chap */
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void println(const char *);
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void
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example(unsigned x)
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{
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switch (x & 6) {
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case 1:
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/* This branch is unreachable. */
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printf("one\n");
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case 0:
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println("0 is reachable");
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break;
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case 1: /* expect: statement not reached */
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println("1 is not reachable");
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break;
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case 2:
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printf("two\n");
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println("2 is reachable");
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break;
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case 6:
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println("6 is reachable");
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break;
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case 7: /* expect: statement not reached */
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println("7 is not reachable");
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break;
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}
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}
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@ -1,4 +1,4 @@
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/* $NetBSD: func.c,v 1.107 2021/05/03 07:08:54 rillig Exp $ */
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/* $NetBSD: func.c,v 1.108 2021/05/15 19:12:14 rillig Exp $ */
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/*
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* Copyright (c) 1994, 1995 Jochen Pohl
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@ -37,7 +37,7 @@
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#include <sys/cdefs.h>
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#if defined(__RCSID) && !defined(lint)
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__RCSID("$NetBSD: func.c,v 1.107 2021/05/03 07:08:54 rillig Exp $");
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__RCSID("$NetBSD: func.c,v 1.108 2021/05/15 19:12:14 rillig Exp $");
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#endif
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#include <stdlib.h>
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@ -439,6 +439,25 @@ named_label(sym_t *sym)
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set_reached(true);
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}
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static void
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check_case_label_bitand(const tnode_t *case_expr, const tnode_t *switch_expr)
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{
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uint64_t case_value, mask;
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if (switch_expr->tn_op != BITAND ||
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switch_expr->tn_right->tn_op != CON)
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return;
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lint_assert(case_expr->tn_op == CON);
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case_value = case_expr->tn_val->v_quad;
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mask = switch_expr->tn_right->tn_val->v_quad;
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if ((case_value & ~mask) != 0) {
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/* statement not reached */
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warning(193);
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}
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}
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static void
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check_case_label_enum(const tnode_t *tn, const cstk_t *ci)
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{
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@ -483,6 +502,7 @@ check_case_label(tnode_t *tn, cstk_t *ci)
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return;
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}
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check_case_label_bitand(tn, ci->c_switch_expr);
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check_case_label_enum(tn, ci);
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lint_assert(ci->c_switch_type != NULL);
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@ -694,12 +714,16 @@ switch1(tnode_t *tn)
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tp->t_tspec = INT;
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}
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/* leak the memory, for check_case_label_bitand */
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expr_save_memory();
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check_getopt_begin_switch();
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expr(tn, true, false, true, false);
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expr(tn, true, false, false, false);
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begin_control_statement(CS_SWITCH);
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cstmt->c_switch = true;
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cstmt->c_switch_type = tp;
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cstmt->c_switch_expr = tn;
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set_reached(false);
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seen_fallthrough = true;
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@ -1,4 +1,4 @@
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/* $NetBSD: lint1.h,v 1.100 2021/04/18 17:47:32 rillig Exp $ */
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/* $NetBSD: lint1.h,v 1.101 2021/05/15 19:12:14 rillig Exp $ */
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/*
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* Copyright (c) 1996 Christopher G. Demetriou. All Rights Reserved.
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@ -416,6 +416,7 @@ typedef struct control_statement {
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bool c_had_return_value : 1; /* had "return expr;" */
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type_t *c_switch_type; /* type of switch expression */
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tnode_t *c_switch_expr;
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case_label_t *c_case_labels; /* list of case values */
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struct memory_block *c_for_expr3_mem; /* saved memory for end of loop
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