Permit certain pointer assignments (grischka-2005-09-25 case_7)
This patch was originally posted in grischka's 2005-09-25 email as
"required fix" case_7 to compile gcc 2.95. It was tweaked by
David A. Wheeler to merge the test case into the standard tcc test suite.

The C99 spec involving this is complicated; see section 6.5.16
(assignment), section 6.2.7 (compatible type and composite type),
and section 6.7.2 (type specifiers). In C99, when they're in separate
translation units, the tag names (if given) must match.

In practice, given:
    struct _s1 { int a, b, c; } *p1 = NULL;
gcc will accept the following assignment without even a warning:
    struct _s2 { int a, b, c; } *p2 = p1;
(Notice that the struct tags are different, but no warning is given.)
This kind of assignment is likely in C programs using OO techniques,
so forbidding them (as tcc currently does) is undesirable.
Note that this patch gives warnings in cases where gcc would not even
give a warning.  The warning is plausible (and highly recommended
in some situations), so it's retained.


diff -ur tinycc-rl-1.0.0/tcc.c tinycc-grischka7/tcc.c
--- tinycc-rl-1.0.0/tcc.c	2007-04-18 14:52:22.000000000 -0400
+++ tinycc-grischka7/tcc.c	2007-05-03 09:26:49.000000000 -0400
@@ -5406,7 +5406,7 @@
             tmp_type1.t &= ~(VT_UNSIGNED | VT_CONSTANT | VT_VOLATILE);
             tmp_type2.t &= ~(VT_UNSIGNED | VT_CONSTANT | VT_VOLATILE);
             if (!is_compatible_types(&tmp_type1, &tmp_type2))
-                goto error;
+                warning("assignment from incompatible pointer type");
         }
         /* check const and volatile */
         if ((!(type1->t & VT_CONSTANT) && (type2->t & VT_CONSTANT)) ||
diff -ur tinycc-rl-1.0.0/tests/tcctest.c tinycc-grischka7/tests/tcctest.c
--- tinycc-rl-1.0.0/tests/tcctest.c	2007-04-18 14:52:22.000000000 -0400
+++ tinycc-grischka7/tests/tcctest.c	2007-05-03 08:22:53.000000000 -0400
@@ -1034,6 +1034,14 @@
     return s1;
 }
 
+void struct_assign_test3(void)
+{
+    // incompatible assigment
+    struct _s1 { int a, b, c; } *p1 = NULL;
+    struct _s2 { int a, b, c; } *p2 = p1; //warning
+    printf("struct assign, 0 -> %x\n", p2);
+}
+
 void struct_assign_test(void)
 {
     struct structa1 lsta1, lsta2;
@@ -1055,6 +1063,7 @@
     printf("before call: %d %d\n", lsta2.f1, lsta2.f2);
     lsta2 = struct_assign_test2(lsta2, 4);
     printf("after call: %d %d\n", lsta2.f1, lsta2.f2);
+    struct_assign_test3();
 }
 
 /* casts to short/char */