compiler warning cleanup: is_signed_type: compare -1 to 1

Comparing -1 to 0 triggers compiler warnings (gcc -Wtype-limits and
-Wbool-compare) and Coverity warning "Macro compares unsigned to 0".

Comparing -1 to 1 instead takes care of silencing those warnings while
keeping the same behavior.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I7d3a2d5a813838cef0e7b42d8c80ccf46f27ac62
Reviewed-on: https://review.lttng.org/c/babeltrace/+/5188
CI-Build: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>

diff --git a/src/compat/bitfield.h b/src/compat/bitfield.h
index 7c1b9307deb1268e9769122130dbc1d008d10aee..e0a3885cb28d36996558529dfc76e88b63785a9e 100644 (file)
--- a/src/compat/bitfield.h
+++ b/src/compat/bitfield.h
@@ -25,30 +25,7 @@
 #error "bitfield.h requires the compiler representation of signed integers to be two's complement."
 #endif
 
-/*
- * _bt_is_signed_type() willingly generates comparison of unsigned
- * expression < 0, which is always false. Silence compiler warnings.
- * GCC versions lower than 4.6.0 do not accept diagnostic pragma inside
- * functions.
- */
-#if defined(__GNUC__) && (__GNUC__ * 10000 + __GNUC_MINOR__ * 100 + __GNUC_PATCHLEVEL__) >= 40600
-# define _BT_DIAG_PUSH                 _Pragma("GCC diagnostic push")
-# define _BT_DIAG_POP                  _Pragma("GCC diagnostic pop")
-
-# define _BT_DIAG_STRINGIFY_1(x)       #x
-# define _BT_DIAG_STRINGIFY(x)         _BT_DIAG_STRINGIFY_1(x)
-
-# define _BT_DIAG_IGNORE(option)       \
-       _Pragma(_BT_DIAG_STRINGIFY(GCC diagnostic ignored option))
-# define _BT_DIAG_IGNORE_TYPE_LIMITS   _BT_DIAG_IGNORE("-Wtype-limits")
-#else
-# define _BT_DIAG_PUSH
-# define _BT_DIAG_POP
-# define _BT_DIAG_IGNORE
-# define _BT_DIAG_IGNORE_TYPE_LIMITS
-#endif
-
-#define _bt_is_signed_type(type)       ((type) -1 < (type) 0)
+#define _bt_is_signed_type(type)       ((type) -1 < (type) 1)
 
 /*
  * Produce a build-time error if the condition `cond` is non-zero.
@@ -371,7 +348,6 @@ do {                                                                        \
        unsigned long _ts = sizeof(type) * CHAR_BIT; /* type size */    \
        unsigned long _start_unit, _end_unit, _this_unit;               \
        unsigned long _end, _cshift; /* _cshift is "complement shift" */ \
-       bool _is_signed_type;                                           \
                                                                        \
        if (!_length) {                                                 \
                *_vptr = 0;                                             \
@@ -383,11 +359,7 @@ do {                                                                       \
        _end_unit = (_end + (_ts - 1)) / _ts;                           \
                                                                        \
        _this_unit = _end_unit - 1;                                     \
-       _BT_DIAG_PUSH                                                   \
-       _BT_DIAG_IGNORE_TYPE_LIMITS                                     \
-       _is_signed_type = _bt_is_signed_type(__typeof__(_v));           \
-       _BT_DIAG_POP                                                    \
-       if (_is_signed_type                                             \
+       if (_bt_is_signed_type(__typeof__(_v))                          \
            && (_ptr[_this_unit] & _bt_lshift((type) 1, (_end % _ts ? _end % _ts : _ts) - 1))) \
                _v = ~(__typeof__(_v)) 0;                               \
        else                                                            \
@@ -443,7 +415,6 @@ do {                                                                        \
        unsigned long _ts = sizeof(type) * CHAR_BIT; /* type size */    \
        unsigned long _start_unit, _end_unit, _this_unit;               \
        unsigned long _end, _cshift; /* _cshift is "complement shift" */ \
-       bool _is_signed_type;                                           \
                                                                        \
        if (!_length) {                                                 \
                *_vptr = 0;                                             \
@@ -455,11 +426,7 @@ do {                                                                       \
        _end_unit = (_end + (_ts - 1)) / _ts;                           \
                                                                        \
        _this_unit = _start_unit;                                       \
-       _BT_DIAG_PUSH                                                   \
-       _BT_DIAG_IGNORE_TYPE_LIMITS                                     \
-       _is_signed_type = _bt_is_signed_type(__typeof__(_v));           \
-       _BT_DIAG_POP                                                    \
-       if (_is_signed_type                                             \
+       if (_bt_is_signed_type(__typeof__(_v))                          \
            && (_ptr[_this_unit] & _bt_lshift((type) 1, _ts - (_start % _ts) - 1))) \
                _v = ~(__typeof__(_v)) 0;                               \
        else                                                            \