bitfields: promote to signed int

For integer promotion with for example arithmetics or
expr_cond (x ? y : z), integral types need to be promoted
to signed if they fit.

According to latest standards, this also applies to bit-field
types taking into account their specific width.

In tcc, VT_BITFIELD set means width < original type width
Field-widths between 33 and 63 are promoted to signed long long
accordingly.

    struct { unsigned long long ullb:35; } s = { 1 };
    #define X (s.ullb - 2)

    int main (void)
    {
        long long Y = X;
        printf("%d %016llx %016llx\n", X < 0, -X, -Y);
        return 0;
    }

Results:
    GCC 4.7 : 0 0000000000000001 FFFFFFF800000001
    MSVC    : 1 0000000000000001 0000000000000001
    TCC     : 1 0000000000000001 0000000000000001

Also, gcc would promote long long bitfields of size < 32
to int as well.  Example:

    struct { unsigned long long x:20; } t = { 123 };
    /* with gcc: */ printf("%d %d\n", t.x, 456);
    /* with tcc: */ printf("%lld %d\n", t.x, 456);

1 files changed, 71 insertions, 0 deletions

diff --git a/tests/tests2/93_integer_promotion.c b/tests/tests2/93_integer_promotion.c
new file mode 100644
index 0000000..a1176fc
--- /dev/null
+++ b/tests/tests2/93_integer_promotion.c
@@ -0,0 +1,71 @@
+/* integer promotion */
+
+int printf(const char*, ...);
+#define promote(s) printf(" %ssigned : %s\n", (s) - 100 < 0 ? "  " : "un", #s);
+
+int main (void)
+{
+    struct {
+        unsigned ub:3;
+        unsigned u:32;
+        unsigned long long ullb:35;
+        unsigned long long ull:64;
+        unsigned char c;
+    } s = { 1, 1, 1 };
+
+    promote(s.ub);
+    promote(s.u);
+    promote(s.ullb);
+    promote(s.ull);
+    promote(s.c);
+    printf("\n");
+
+    promote((1 ? s.ub : 1));
+    promote((1 ? s.u : 1));
+    promote((1 ? s.ullb : 1));
+    promote((1 ? s.ull : 1));
+    promote((1 ? s.c : 1));
+    printf("\n");
+
+    promote(s.ub << 1);
+    promote(s.u << 1);
+    promote(s.ullb << 1);
+    promote(s.ull << 1);
+    promote(s.c << 1);
+    printf("\n");
+
+    promote(+s.ub);
+    promote(+s.u);
+    promote(+s.ullb);
+    promote(+s.ull);
+    promote(+s.c);
+    printf("\n");
+
+    promote(-s.ub);
+    promote(-s.u);
+    promote(-s.ullb);
+    promote(-s.ull);
+    promote(-s.c);
+    printf("\n");
+
+    promote(~s.ub);
+    promote(~s.u);
+    promote(~s.ullb);
+    promote(~s.ull);
+    promote(~s.c);
+    printf("\n");
+
+    promote(!s.ub);
+    promote(!s.u);
+    promote(!s.ullb);
+    promote(!s.ull);
+    promote(!s.c);
+    printf("\n");
+
+    promote(+(unsigned)s.ub);
+    promote(-(unsigned)s.ub);
+    promote(~(unsigned)s.ub);
+    promote(!(unsigned)s.ub);
+
+    return 0;
+}