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Use __assume(0) for unreachable code path in msvc

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msvc will optimize away the condition check.
This commit is contained in:
Ma Lin
2021-09-27 19:23:57 +08:00
parent e5ba858270
commit ae986fcdb8
6 changed files with 113 additions and 32 deletions
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lib/common/bitstream.h
+9 -3
View File
@@ -143,10 +143,16 @@ MEM_STATIC unsigned BIT_highbit32 (U32 val)
{
# if defined(_MSC_VER) /* Visual */
# if STATIC_BMI2 == 1
return _lzcnt_u32(val) ^ 31;
return _lzcnt_u32(val) ^ 31;
# else
unsigned long r;
return _BitScanReverse(&r, val) ? (unsigned)r : 0;
if (val != 0) {
unsigned long r;
_BitScanReverse(&r, val);
return (unsigned)r;
} else {
/* Should not reach this code path */
__assume(0);
}
# endif
# elif defined(__GNUC__) && (__GNUC__ >= 3) /* Use GCC Intrinsic */
return __builtin_clz (val) ^ 31;
lib/common/entropy_common.c
+8 -2
View File
@@ -43,8 +43,14 @@ static U32 FSE_ctz(U32 val)
assert(val != 0);
{
# if defined(_MSC_VER) /* Visual */
unsigned long r;
return _BitScanForward(&r, val) ? (unsigned)r : 0;
if (val != 0) {
unsigned long r;
_BitScanForward(&r, val);
return (unsigned)r;
} else {
/* Should not reach this code path */
__assume(0);
}
# elif defined(__GNUC__) && (__GNUC__ >= 3) /* GCC Intrinsic */
return __builtin_ctz(val);
# elif defined(__ICCARM__) /* IAR Intrinsic */
lib/common/zstd_internal.h
+24 -6
View File
@@ -358,8 +358,14 @@ MEM_STATIC U32 ZSTD_highbit32(U32 val) /* compress, dictBuilder, decodeCorpus
# if STATIC_BMI2 == 1
return _lzcnt_u32(val)^31;
# else
unsigned long r;
return _BitScanReverse(&r, val) ? (unsigned)r : 0;
if (val != 0) {
unsigned long r;
_BitScanReverse(&r, val);
return (unsigned)r;
} else {
/* Should not reach this code path */
__assume(0);
}
# endif
# elif defined(__GNUC__) && (__GNUC__ >= 3) /* GCC Intrinsic */
return __builtin_clz (val) ^ 31;
@@ -391,8 +397,14 @@ MEM_STATIC unsigned ZSTD_countTrailingZeros(size_t val)
# if STATIC_BMI2
return _tzcnt_u64(val);
# else
unsigned long r;
return _BitScanForward64( &r, (U64)val ) ? (unsigned)(r >> 3) : 0;
if (val != 0) {
unsigned long r;
_BitScanForward64(&r, (U64)val);
return (unsigned)(r >> 3);
} else {
/* Should not reach this code path */
__assume(0);
}
# endif
# elif defined(__GNUC__) && (__GNUC__ >= 4)
return __builtin_ctzll((U64)val);
@@ -409,8 +421,14 @@ MEM_STATIC unsigned ZSTD_countTrailingZeros(size_t val)
# endif
} else { /* 32 bits */
# if defined(_MSC_VER)
unsigned long r;
return _BitScanForward( &r, (U32)val ) ? (unsigned)(r >> 3) : 0;
if (val != 0) {
unsigned long r;
_BitScanForward(&r, (U32)val);
return (unsigned)(r >> 3);
} else {
/* Should not reach this code path */
__assume(0);
}
# elif defined(__GNUC__) && (__GNUC__ >= 3)
return (__builtin_ctz((U32)val) >> 3);
# else