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[src/trunk]: src/usr.bin/xlint/lint1 lint: do not warn about loss in accuracy...
details: https://anonhg.NetBSD.org/src/rev/a24415fb4ac3
branches: trunk
changeset: 366416:a24415fb4ac3
user: rillig <rillig%NetBSD.org@localhost>
date: Thu May 26 09:26:00 2022 +0000
description:
lint: do not warn about loss in accuracy if the actual value fits
The expression 'any & 0xff' can always be assigned to 'uint8_t' without
loss of any value bits. In the same way, '(any & 0xff) << 8' can always
be assigned to 'uint16_t'.
Previously, lint warned about these cases. Fix these wrong warnings by
tracking the possible values of integer expressions across a single
expression.
Fixes PR 36668, so that <sys/endian.h> does not need to be cluttered
with useless casts anymore.
diffstat:
tests/usr.bin/xlint/lint1/msg_132.c | 16 ++-
tests/usr.bin/xlint/lint1/msg_132.exp | 1 -
usr.bin/xlint/lint1/tree.c | 170 ++++++++++++++++++++++++++++++---
3 files changed, 164 insertions(+), 23 deletions(-)
diffs (249 lines):
diff -r 4e4f9d39889d -r a24415fb4ac3 tests/usr.bin/xlint/lint1/msg_132.c
--- a/tests/usr.bin/xlint/lint1/msg_132.c Thu May 26 08:06:58 2022 +0000
+++ b/tests/usr.bin/xlint/lint1/msg_132.c Thu May 26 09:26:00 2022 +0000
@@ -1,4 +1,4 @@
-/* $NetBSD: msg_132.c,v 1.10 2022/05/26 07:03:03 rillig Exp $ */
+/* $NetBSD: msg_132.c,v 1.11 2022/05/26 09:26:00 rillig Exp $ */
# 3 "msg_132.c"
// Test for message: conversion from '%s' to '%s' may lose accuracy [132]
@@ -148,15 +148,23 @@
/*
* PR 36668 notices that lint wrongly complains about the possible loss.
- * The expression 'uint8_t << 8' is guaranteed to fit into an 'unsigned short'.
- * 'unsigned short | unsigned char' is guaranteed to fit into 'unsigned short'
+ *
+ * The expression 'u8_t << 8' is guaranteed to fit into an 'u16_t', and its
+ * lower 8 bits are guaranteed to be clear. 'u16_t | u8_t' is guaranteed to
+ * fit into 'u16_t'.
+ *
+ * Since tree.c 1.444 from 2022-05-26, lint tracks simple bitwise and
+ * arithmetic constraints across a single expression.
*/
static inline u16_t
be16dec(const void *buf)
{
const u8_t *p = buf;
- /* expect+1: warning: conversion from 'int' to 'unsigned short' may lose accuracy [132] */
+ /*
+ * Before tree.c 1.444 from 2022-05-26, lint complained that the
+ * conversion from 'int' to 'unsigned short' may lose accuracy.
+ */
return ((u16_t)p[0]) << 8 | p[1];
}
diff -r 4e4f9d39889d -r a24415fb4ac3 tests/usr.bin/xlint/lint1/msg_132.exp
--- a/tests/usr.bin/xlint/lint1/msg_132.exp Thu May 26 08:06:58 2022 +0000
+++ b/tests/usr.bin/xlint/lint1/msg_132.exp Thu May 26 09:26:00 2022 +0000
@@ -25,4 +25,3 @@
msg_132.c(125): error: operands of '+' have incompatible types (pointer != double) [107]
msg_132.c(125): warning: function 'cover_build_plus_minus' expects to return value [214]
msg_132.c(141): warning: conversion from 'unsigned long long' to 'int' may lose accuracy [132]
-msg_132.c(160): warning: conversion from 'int' to 'unsigned short' may lose accuracy [132]
diff -r 4e4f9d39889d -r a24415fb4ac3 usr.bin/xlint/lint1/tree.c
--- a/usr.bin/xlint/lint1/tree.c Thu May 26 08:06:58 2022 +0000
+++ b/usr.bin/xlint/lint1/tree.c Thu May 26 09:26:00 2022 +0000
@@ -1,4 +1,4 @@
-/* $NetBSD: tree.c,v 1.443 2022/05/26 06:43:58 rillig Exp $ */
+/* $NetBSD: tree.c,v 1.444 2022/05/26 09:26:00 rillig Exp $ */
/*
* Copyright (c) 1994, 1995 Jochen Pohl
@@ -37,7 +37,7 @@
#include <sys/cdefs.h>
#if defined(__RCSID)
-__RCSID("$NetBSD: tree.c,v 1.443 2022/05/26 06:43:58 rillig Exp $");
+__RCSID("$NetBSD: tree.c,v 1.444 2022/05/26 09:26:00 rillig Exp $");
#endif
#include <float.h>
@@ -50,6 +50,15 @@
#include "lint1.h"
#include "cgram.h"
+typedef struct integer_constraints {
+ int64_t smin; /* signed minimum */
+ int64_t smax; /* signed maximum */
+ uint64_t umin; /* unsigned minimum */
+ uint64_t umax; /* unsigned maximum */
+ uint64_t bset; /* bits that are definitely set */
+ uint64_t bclr; /* bits that are definitely clear */
+} integer_constraints;
+
static tnode_t *build_integer_constant(tspec_t, int64_t);
static void check_pointer_comparison(op_t,
const tnode_t *, const tnode_t *);
@@ -96,6 +105,137 @@
extern sig_atomic_t fpe;
+static integer_constraints
+ic_any(const type_t *tp)
+{
+ integer_constraints c;
+
+ lint_assert(is_integer(tp->t_tspec));
+ unsigned int sz = type_size_in_bits(tp);
+ uint64_t vbits = value_bits(sz);
+ if (is_uinteger(tp->t_tspec)) {
+ c.smin = INT64_MIN;
+ c.smax = INT64_MAX;
+ c.umin = 0;
+ c.umax = vbits;
+ c.bset = 0;
+ c.bclr = ~c.umax;
+ } else {
+ c.smin = (int64_t)-1 - (int64_t)(vbits >> 1);
+ c.smax = (int64_t)(vbits >> 1);
+ c.umin = 0;
+ c.umax = UINT64_MAX;
+ c.bset = 0;
+ c.bclr = 0;
+ }
+ return c;
+}
+
+static integer_constraints
+ic_con(const type_t *tp, const val_t *v)
+{
+ integer_constraints c;
+
+ lint_assert(is_integer(tp->t_tspec));
+ int64_t s = v->v_quad;
+ uint64_t u = (uint64_t)s;
+ c.smin = s;
+ c.smax = s;
+ c.umin = u;
+ c.umax = u;
+ c.bset = u;
+ c.bclr = ~u;
+ return c;
+}
+
+static integer_constraints
+ic_cvt(const type_t *ntp, const type_t *otp, integer_constraints a)
+{
+
+ if (type_size_in_bits(ntp) > type_size_in_bits(otp) &&
+ is_uinteger(otp->t_tspec))
+ return a;
+ return ic_any(ntp);
+}
+
+static integer_constraints
+ic_bitand(integer_constraints a, integer_constraints b)
+{
+ integer_constraints c;
+
+ c.smin = INT64_MIN;
+ c.smax = INT64_MAX;
+ c.umin = 0;
+ c.umax = UINT64_MAX;
+ c.bset = a.bset & b.bset;
+ c.bclr = a.bclr | b.bclr;
+ return c;
+}
+
+static integer_constraints
+ic_bitor(integer_constraints a, integer_constraints b)
+{
+ integer_constraints c;
+
+ c.smin = INT64_MIN;
+ c.smax = INT64_MAX;
+ c.umin = 0;
+ c.umax = UINT64_MAX;
+ c.bset = a.bset | b.bset;
+ c.bclr = a.bclr & b.bclr;
+ return c;
+}
+
+static integer_constraints
+ic_shl(const type_t *tp, integer_constraints a, integer_constraints b)
+{
+ integer_constraints c;
+ unsigned int amount;
+
+ if (b.smin == b.smax && b.smin >= 0 && b.smin < 64)
+ amount = (unsigned int)b.smin;
+ else if (b.umin == b.umax && b.umin < 64)
+ amount = (unsigned int)b.umin;
+ else
+ return ic_any(tp);
+
+ c.smin = INT64_MIN;
+ c.smax = INT64_MAX;
+ c.umin = 0;
+ c.umax = UINT64_MAX;
+ c.bset = a.bset << amount;
+ c.bclr = a.bclr << amount | (((uint64_t)1 << amount) - 1);
+ return c;
+}
+
+static integer_constraints
+ic_expr(const tnode_t *tn)
+{
+ integer_constraints lc, rc;
+
+ switch (tn->tn_op) {
+ case CON:
+ return ic_con(tn->tn_type, tn->tn_val);
+ case CVT:
+ lc = ic_expr(tn->tn_left);
+ return ic_cvt(tn->tn_type, tn->tn_left->tn_type, lc);
+ case SHL:
+ lc = ic_expr(tn->tn_left);
+ rc = ic_expr(tn->tn_right);
+ return ic_shl(tn->tn_type, lc, rc);
+ case BITAND:
+ lc = ic_expr(tn->tn_left);
+ rc = ic_expr(tn->tn_right);
+ return ic_bitand(lc, rc);
+ case BITOR:
+ lc = ic_expr(tn->tn_left);
+ rc = ic_expr(tn->tn_right);
+ return ic_bitor(lc, rc);
+ default:
+ return ic_any(tn->tn_type);
+ }
+}
+
static const char *
op_name(op_t op)
{
@@ -2211,22 +2351,16 @@
can_represent(const type_t *tp, const tnode_t *tn)
{
- if (tn->tn_op == BITAND) {
- const tnode_t *rn = tn->tn_right;
- tspec_t nt;
-
- if (!(rn != NULL && rn->tn_op == CON &&
- is_integer(rn->tn_type->t_tspec)))
- return false;
-
- uint64_t nmask = value_bits(size_in_bits(nt = tp->t_tspec));
- if (!is_uinteger(nt))
- nmask >>= 1;
-
- uint64_t omask = (uint64_t)rn->tn_val->v_quad;
- if ((omask & ~nmask) == 0)
- return true;
- }
+ debug_step("%s: type '%s'", __func__, type_name(tp));
+ debug_node(tn);
+
+ uint64_t nmask = value_bits(type_size_in_bits(tp));
+ if (!is_uinteger(tp->t_tspec))
+ nmask >>= 1;
+
+ integer_constraints c = ic_expr(tn);
+ if ((~c.bclr & ~nmask) == 0)
+ return true;
return false;
}
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