Fix handling of unevaluated subexpression of const

we were emitting error messages for something like
'static int i = 2 || 1/0', even though the exception would be in
the unevaluated part.  This doesn't destroy const-ness, so we must
accept it.  This requires splitting the nocode_wanted values a bit more,
so that nocode_wanted due to const_wanted can be differentiated from
nocode_wanted due to non-evaluation.

tccgen.c

@@ -53,6 +53,7 @@ static SValue _vstack[1 + VSTACK_SIZE];
 
 ST_DATA int const_wanted; /* true if constant wanted */
 ST_DATA int nocode_wanted; /* no code generation wanted */
+#define unevalmask 0xffff /* unevaluated subexpression */
 #define NODATA_WANTED (nocode_wanted > 0) /* no static data output wanted either */
 #define STATIC_DATA_WANTED (nocode_wanted & 0xC0000000) /* only static data output */
 
@@ -2273,7 +2274,7 @@ static void gen_opic(int op)
         case TOK_UMOD:
             /* if division by zero, generate explicit division */
             if (l2 == 0) {
-                if (const_wanted)
+                if (const_wanted && !(nocode_wanted & unevalmask))
                     tcc_error("division by zero in constant");
                 goto general_case;
             }
@@ -5104,7 +5105,7 @@ ST_FUNC void unary(void)
             }
         } else if (tok == '{') {
 	    int saved_nocode_wanted = nocode_wanted;
-            if (const_wanted)
+            if (const_wanted && !(nocode_wanted & unevalmask))
                 tcc_error("expected constant");
             /* save all registers */
             save_regs(0);
@@ -6152,9 +6153,9 @@ ST_FUNC void gexpr(void)
 static void expr_const1(void)
 {
     const_wanted++;
-    nocode_wanted++;
+    nocode_wanted += unevalmask + 1;
     expr_cond();
-    nocode_wanted--;
+    nocode_wanted -= unevalmask + 1;
     const_wanted--;
 }
 

tests/tcctest.c

@@ -950,6 +950,8 @@ void expr2_test()
     printf("res= %d %d\n", a, b);
 }
 
+int const_len_ar[sizeof(1/0)]; /* div-by-zero, but in unevaluated context */
+
 void constant_expr_test()
 {
     int a;
@@ -958,6 +960,7 @@ void constant_expr_test()
     printf("%d\n", a * 16);
     printf("%d\n", a * 1);
     printf("%d\n", a + 0);
+    printf("%d\n", sizeof(const_len_ar));
 }
 
 int tab4[10];
@@ -1845,6 +1848,8 @@ arrtype2 sinit22 = {5,6,7};
 int sinit23[2] = { "astring" ? sizeof("astring") : -1,
 		   &sinit23 ? 42 : -1 };
 
+int sinit24 = 2 || 1 / 0; /* exception in constant but unevaluated context */
+
 extern int external_inited = 42;
 
 void init_test(void)
@@ -1959,6 +1964,7 @@ void init_test(void)
     printf("arrtype6: %d\n", sizeof(arrtype2));
 
     printf("sinit23= %d %d\n", sinit23[0], sinit23[1]);
+    printf("sinit24=%d\n", sinit24);
     printf("linit18= %d %d\n", linit18[0], linit18[1]);
 }
 

tests/tests2/60_errors_and_warnings.c

@@ -151,6 +151,10 @@ int ga = 0.42 { 2 };
 struct S { int a, b; };
 struct T { struct S x; };
 struct T gt = { 42 a: 1, 43 };
+#elif defined test_invalid_4
+enum E {
+    x = 1 / 0
+};
 #elif defined test_conflicting_types
 int i;
 void foo(void) {

tests/tests2/60_errors_and_warnings.expect

@@ -72,37 +72,40 @@
 [test_invalid_3]
 60_errors_and_warnings.c:153: error: ',' expected (got "a")
 
+[test_invalid_4]
+60_errors_and_warnings.c:157: error: division by zero in constant
+
 [test_conflicting_types]
-60_errors_and_warnings.c:159: error: incompatible types for redefinition of 'i'
+60_errors_and_warnings.c:163: error: incompatible types for redefinition of 'i'
 
 [test_nested_types]
-60_errors_and_warnings.c:166: error: struct/union/enum already defined
+60_errors_and_warnings.c:170: error: struct/union/enum already defined
 
 [test_vla_1]
-60_errors_and_warnings.c:173: error: need explicit inner array size in VLAs
+60_errors_and_warnings.c:177: error: need explicit inner array size in VLAs
 
 [test_invalid_alignas]
-60_errors_and_warnings.c:177: error: identifier expected
+60_errors_and_warnings.c:181: error: identifier expected
 
 [test_static_assert]
-60_errors_and_warnings.c:183: error: "ONE is not 1"
+60_errors_and_warnings.c:187: error: "ONE is not 1"
 
 [test_void_array]
-60_errors_and_warnings.c:186: error: declaration of an array of incomplete type elements
+60_errors_and_warnings.c:190: error: declaration of an array of incomplete type elements
 
 [test_incomplete_enum_array]
-60_errors_and_warnings.c:189: error: declaration of an array of incomplete type elements
+60_errors_and_warnings.c:193: error: declaration of an array of incomplete type elements
 
 [test_incomplete_struct_array]
-60_errors_and_warnings.c:192: error: declaration of an array of incomplete type elements
+60_errors_and_warnings.c:196: error: declaration of an array of incomplete type elements
 
 [test_const_fun_array]
-60_errors_and_warnings.c:196: error: declaration of an array of functions
+60_errors_and_warnings.c:200: error: declaration of an array of functions
 
 [test_incomplete_array_array]
 
 [test_extern_array]
-60_errors_and_warnings.c:212: error: incompatible types for redefinition of 'x'
+60_errors_and_warnings.c:216: error: incompatible types for redefinition of 'x'
 
 [test_func_1]
 hello: a = 123
@@ -111,17 +114,17 @@ hello: a = 123
 hello: a = 123
 
 [test_func_3]
-60_errors_and_warnings.c:242: warning: static storage ignored for redefinition of 'hello'
+60_errors_and_warnings.c:246: warning: static storage ignored for redefinition of 'hello'
 hello: a = 123
 
 [test_func_4]
 hello: a = 123
 
 [test_func_5]
-60_errors_and_warnings.c:242: error: incompatible types for redefinition of 'hello'
+60_errors_and_warnings.c:246: error: incompatible types for redefinition of 'hello'
 
 [test_func_6]
-60_errors_and_warnings.c:230: error: function without file scope cannot be static
+60_errors_and_warnings.c:234: error: function without file scope cannot be static
 
 [test_var_1]
 main : 1 ; 1
@@ -134,6 +137,6 @@ main : 2 ; 2
 bar  : 3 ; 3
 
 [test_var_3]
-60_errors_and_warnings.c:274: error: incompatible types for redefinition of 'xxx'
+60_errors_and_warnings.c:278: error: incompatible types for redefinition of 'xxx'
 
 [test_var_4]