nasm_assert(): try to run at compile time if possible

Try to make nasm_assert() do a static assert if the argument can be
evaluated at compile time by any particular compiler. We also provide
nasm_try_static_assert() which will assert a compile-time expression
if and only if we can determine we have a constant at compile time
*and* we know that the compiler has a way to handle it.

Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>

configure.ac

@@ -207,9 +207,10 @@ PA_HAVE_FUNC(_byteswap_ulong, (0))
 PA_HAVE_FUNC(_byteswap_uint64, (0))
 
 dnl
-dnl Check for __builtin_constant_p()
+dnl Some rather useful gcc extensions...
 dnl
 PA_HAVE_FUNC(__builtin_constant_p, (0))
+PA_HAVE_FUNC(__builtin_choose_expr, (0,1,2))
 
 dnl
 dnl Check for supported gcc attributes; some compilers (e.g. Sun CC)

include/compiler.h

@@ -358,6 +358,27 @@ size_t strnlen(const char *s, size_t maxlen);
 # define is_constant(x) false
 #endif
 
+/*
+ * If we can guarantee that a particular expression is constant, use it,
+ * otherwise use a different version.
+ */
+#if defined(__GNUC__) && (__GNUC__ >= 3)
+# define not_pedantic_start                             \
+    _Pragma("GCC diagnostic push")                      \
+    _Pragma("GCC diagnostic ignored \"-Wpedantic\"")
+# define not_pedantic_end                       \
+    _Pragma("GCC diagnostic pop")
+#else
+# define not_pedantic_start
+# define not_pedantic_end
+#endif
+
+#ifdef HAVE___BUILTIN_CHOOSE_EXPR
+# define if_constant(x,y) __builtin_choose_expr(is_constant(x),(x),(y))
+#else
+# define if_constant(x,y) (y)
+#endif
+
 /*
  * The autoconf documentation states:
  *

include/nasmlib.h

@@ -113,34 +113,62 @@ static inline size_t nasm_aprintf_size(void)
 void nasm_read(void *, size_t, FILE *);
 void nasm_write(const void *, size_t, FILE *);
 
-/*
- * NASM assert failure
- */
-fatal_func nasm_assert_failed(const char *, int, const char *);
-#define nasm_assert(x)                                          \
-    do {                                                        \
-        if (unlikely(!(x)))                                     \
-            nasm_assert_failed(__FILE__,__LINE__,#x);           \
-    } while (0)
-
 /*
  * NASM failure at build time if the argument is false
  */
 #ifdef static_assert
-# define nasm_static_assert(x) static_assert(x, #x)
+# define nasm_static_assert(x) static_assert((x), #x)
 #elif defined(HAVE_FUNC_ATTRIBUTE_ERROR) && defined(__OPTIMIZE__)
 # define nasm_static_assert(x)						\
+    do {								\
         if (!(x)) {                                                     \
             extern void __attribute__((error("assertion " #x " failed")))   \
                 _nasm_static_fail(void);				\
             _nasm_static_fail();                                        \
-    }
+	}								\
+    } while (0)
 #else
 /* See http://www.drdobbs.com/compile-time-assertions/184401873 */
 # define nasm_static_assert(x) \
     do { enum { _static_assert_failed = 1/(!!(x)) }; } while (0)
 #endif
 
+/*
+ * conditional static assert, if we know it is possible to determine
+ * the assert value at compile time. Since if_constant triggers
+ * pedantic warnings on gcc, turn them off explicitly around this code.
+ */
+#ifdef static_assert
+# define nasm_try_static_assert(x)					\
+    do {								\
+        not_pedantic_start						\
+	static_assert(if_constant(x, true), #x);			\
+	not_pedantic_end						\
+    } while (0)
+#elif defined(HAVE_FUNC_ATTRIBUTE_ERROR) && defined(__OPTIMIZE__)
+# define nasm_try_static_assert(x)                                      \
+    do {								\
+        if (!if_constant(x, true)) {					\
+	    extern void __attribute__((error("assertion " #x " failed"))) \
+		_nasm_static_fail(void);				\
+	    _nasm_static_fail();					\
+	}								\
+    } while (0)
+#else
+# define nasm_try_static_assert(x) ((void)0)
+#endif
+
+/*
+ * NASM assert failure
+ */
+fatal_func nasm_assert_failed(const char *, int, const char *);
+#define nasm_assert(x)                                          \
+    do {                                                        \
+        nasm_try_static_assert(x);                              \
+        if (unlikely(!(x)))                                     \
+            nasm_assert_failed(__FILE__,__LINE__,#x);           \
+    } while (0)
+
 /* Utility function to generate a string for an invalid enum */
 const char *invalid_enum_str(int);
 

output/codeview.c

@@ -654,7 +654,7 @@ static uint16_t write_symbolinfo_properties(struct coff_Section *sect,
     else if (win32)
         section_write16(sect, 0x0006); /* machine */
     else
-        nasm_assert(!"neither win32 nor win64 are set!");
+        nasm_panic("neither win32 nor win64 are set!");
     section_write16(sect, 0); /* verFEMajor */
     section_write16(sect, 0); /* verFEMinor */
     section_write16(sect, 0); /* verFEBuild */
@@ -711,7 +711,7 @@ static uint16_t write_symbolinfo_symbols(struct coff_Section *sect)
             section_write8(sect, 0); /* FLAG */
             break;
         default:
-            nasm_assert(!"unknown symbol type");
+            nasm_panic("unknown symbol type");
         }
 
         section_wbytes(sect, sym->name, strlen(sym->name) + 1);

output/outbin.c

@@ -1507,7 +1507,7 @@ static void write_srecord(unsigned int len,  unsigned int alen,
     case 4:
 	break;
     default:
-	nasm_assert(0);
+	panic();
 	break;
     }