Fix null pointer constants

an expression like 'i*0', even though it's value is constant and
can be evaluated at compile time is not an integer constant expression,
and hence no null pointer constant, and therefore the conditional
operator doesn't select the other type.

tcc.h

@@ -1029,6 +1029,8 @@ struct filespec {
 #define VT_SYM       0x0200  /* a symbol value is added */
 #define VT_MUSTCAST  0x0C00  /* value must be casted to be correct (used for
                                 char/short stored in integer registers) */
+#define VT_NONCONST  0x1000  /* VT_CONST, but not an (C standard) integer
+                                constant expression */
 #define VT_MUSTBOUND 0x4000  /* bound checking must be done before
                                 dereferencing value */
 #define VT_BOUNDED   0x8000  /* value is bounded. The address of the

tccgen.c

@@ -2187,6 +2187,7 @@ static void gen_opic(int op)
     int t2 = v2->type.t & VT_BTYPE;
     int c1 = (v1->r & (VT_VALMASK | VT_LVAL | VT_SYM)) == VT_CONST;
     int c2 = (v2->r & (VT_VALMASK | VT_LVAL | VT_SYM)) == VT_CONST;
+    int nonconst = (v1->r | v2->r) & VT_NONCONST;
     uint64_t l1 = c1 ? v1->c.i : 0;
     uint64_t l2 = c2 ? v2->c.i : 0;
     int shm = (t1 == VT_LLONG) ? 63 : 31;
@@ -2253,6 +2254,7 @@ static void gen_opic(int op)
         v1->c.i = l1;
         vtop--;
     } else {
+        nonconst = VT_NONCONST;
         /* if commutative ops, put c2 as constant */
         if (c1 && (op == '+' || op == '&' || op == '^' || 
                    op == '|' || op == '*' || op == TOK_EQ || op == TOK_NE)) {
@@ -2326,6 +2328,8 @@ static void gen_opic(int op)
                     gen_opi(op);
         }
     }
+    if (vtop->r == VT_CONST)
+      vtop->r |= nonconst;
 }
 
 #if defined TCC_TARGET_X86_64 || defined TCC_TARGET_I386
@@ -2609,7 +2613,7 @@ static int pointed_size(CType *type)
 
 static inline int is_null_pointer(SValue *p)
 {
-    if ((p->r & (VT_VALMASK | VT_LVAL | VT_SYM)) != VT_CONST)
+    if ((p->r & (VT_VALMASK | VT_LVAL | VT_SYM | VT_NONCONST)) != VT_CONST)
         return 0;
     return ((p->type.t & VT_BTYPE) == VT_INT && (uint32_t)p->c.i == 0) ||
         ((p->type.t & VT_BTYPE) == VT_LLONG && p->c.i == 0) ||

tests/tests2/94_generic.c

@@ -92,6 +92,9 @@ int main()
 
 	//void ptrs get chosen preferentially; qualifs still combine
 	_Generic( 0?(int volatile*)0: (void const*)1, void volatile const*: (void)0);
+        //but this is no null-ptr constant, so fallback to void-choice
+        i = 0;
+        _Generic( 1?(void*)(i*0LL):&i, void*:0);
 	//like gcc but not clang, don't treat (void* const as the null-ptr constant)
 	_Generic( 0?(int volatile*)0: (void const*)0, void volatile const*: (void)0);