From: Ma Lin <malincns@163.com>
Date: Sun, 26 Sep 2021 02:41:39 +0000 (+0800)
Subject: Use __assume(0) for unreachable code path in msvc
X-Git-Tag: v1.5.1~1^2~76^2~1
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ae986fcdb861c44ee4267fc4b3dcf0a4cd2ee724;p=thirdparty%2Fzstd.git

Use __assume(0) for unreachable code path in msvc

msvc will optimize away the condition check.
---

diff --git a/lib/common/bitstream.h b/lib/common/bitstream.h
index cefa1196b..696719eaf 100644
--- a/lib/common/bitstream.h
+++ b/lib/common/bitstream.h
@@ -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;
diff --git a/lib/common/entropy_common.c b/lib/common/entropy_common.c
index dd80b2ccc..3ac00255f 100644
--- a/lib/common/entropy_common.c
+++ b/lib/common/entropy_common.c
@@ -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 */
diff --git a/lib/common/zstd_internal.h b/lib/common/zstd_internal.h
index 246022c5f..4db5b00a7 100644
--- a/lib/common/zstd_internal.h
+++ b/lib/common/zstd_internal.h
@@ -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
diff --git a/lib/compress/zstd_compress_internal.h b/lib/compress/zstd_compress_internal.h
index bc30daa75..cf0b8061a 100644
--- a/lib/compress/zstd_compress_internal.h
+++ b/lib/compress/zstd_compress_internal.h
@@ -672,8 +672,14 @@ static unsigned ZSTD_NbCommonBytes (size_t val)
 #           if STATIC_BMI2
                 return _tzcnt_u64(val) >> 3;
 #           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) >> 3);
@@ -690,8 +696,14 @@ static unsigned ZSTD_NbCommonBytes (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
@@ -708,8 +720,14 @@ static unsigned ZSTD_NbCommonBytes (size_t val)
 #           if STATIC_BMI2
 			    return _lzcnt_u64(val) >> 3;
 #           else
-			    unsigned long r;
-			    return _BitScanReverse64(&r, (U64)val) ? (unsigned)(r >> 3) : 0;
+                if (val != 0) {
+                    unsigned long r;
+                    _BitScanReverse64(&r, (U64)val);
+                    return (unsigned)(r >> 3);
+                } else {
+                    /* Should not reach this code path */
+                    __assume(0);
+                }
 #           endif
 #       elif defined(__GNUC__) && (__GNUC__ >= 4)
             return (__builtin_clzll(val) >> 3);
@@ -723,8 +741,14 @@ static unsigned ZSTD_NbCommonBytes (size_t val)
 #       endif
         } else { /* 32 bits */
 #       if defined(_MSC_VER)
-            unsigned long r;
-            return _BitScanReverse( &r, (unsigned long)val ) ? (unsigned)(r >> 3) : 0;
+            if (val != 0) {
+                unsigned long r;
+                _BitScanReverse(&r, (unsigned long)val);
+                return (unsigned)(r >> 3);
+            } else {
+                /* Should not reach this code path */
+                __assume(0);
+            }
 #       elif defined(__GNUC__) && (__GNUC__ >= 3)
             return (__builtin_clz((U32)val) >> 3);
 #       else
diff --git a/lib/compress/zstd_lazy.c b/lib/compress/zstd_lazy.c
index ac84b479f..cbac712a5 100644
--- a/lib/compress/zstd_lazy.c
+++ b/lib/compress/zstd_lazy.c
@@ -881,11 +881,14 @@ typedef U64 ZSTD_VecMask;   /* Clarifies when we are interacting with a U64 repr
 static U32 ZSTD_VecMask_next(ZSTD_VecMask val) {
     assert(val != 0);
 #   if defined(_MSC_VER) && defined(_WIN64)
-    {
-        unsigned long r;
-        /* _BitScanForward64 is not defined outside of x64 */
-        return _BitScanForward64(&r, val) ? (U32)r : 0;
-    }
+        if (val != 0) {
+            unsigned long r;
+            _BitScanForward64(&r, val);
+            return (U32)(r);
+        } else {
+            /* Should not reach this code path */
+            __assume(0);
+        }
 #   elif (defined(__GNUC__) && ((__GNUC__ > 3) || ((__GNUC__ == 3) && (__GNUC_MINOR__ >= 4))))
     if (sizeof(size_t) == 4) {
         U32 mostSignificantWord = (U32)(val >> 32);
diff --git a/lib/dictBuilder/zdict.c b/lib/dictBuilder/zdict.c
index ea00eafc7..d93b202e7 100644
--- a/lib/dictBuilder/zdict.c
+++ b/lib/dictBuilder/zdict.c
@@ -135,8 +135,14 @@ static unsigned ZDICT_NbCommonBytes (size_t val)
     if (MEM_isLittleEndian()) {
         if (MEM_64bits()) {
 #       if defined(_MSC_VER) && defined(_WIN64)
-            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);
+            }
 #       elif defined(__GNUC__) && (__GNUC__ >= 3)
             return (unsigned)(__builtin_ctzll((U64)val) >> 3);
 #       else
@@ -145,8 +151,14 @@ static unsigned ZDICT_NbCommonBytes (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 (unsigned)(__builtin_ctz((U32)val) >> 3);
 #       else
@@ -157,8 +169,14 @@ static unsigned ZDICT_NbCommonBytes (size_t val)
     } else {  /* Big Endian CPU */
         if (MEM_64bits()) {
 #       if defined(_MSC_VER) && defined(_WIN64)
-            unsigned long r;
-            return _BitScanReverse64(&r, val) ? (unsigned)(r >> 3) : 0;
+            if (val != 0) {
+                unsigned long r;
+                _BitScanReverse64(&r, val);
+                return (unsigned)(r >> 3);
+            } else {
+                /* Should not reach this code path */
+                __assume(0);
+            }
 #       elif defined(__GNUC__) && (__GNUC__ >= 3)
             return (unsigned)(__builtin_clzll(val) >> 3);
 #       else
@@ -171,8 +189,14 @@ static unsigned ZDICT_NbCommonBytes (size_t val)
 #       endif
         } else { /* 32 bits */
 #       if defined(_MSC_VER)
-            unsigned long r;
-            return _BitScanReverse(&r, (unsigned long)val) ? (unsigned)(r >> 3) : 0;
+            if (val != 0) {
+                unsigned long r;
+                _BitScanReverse(&r, (unsigned long)val);
+                return (unsigned)(r >> 3);
+            } else {
+                /* Should not reach this code path */
+                __assume(0);
+            }
 #       elif defined(__GNUC__) && (__GNUC__ >= 3)
             return (unsigned)(__builtin_clz((U32)val) >> 3);
 #       else