tccgen: update "Fix invalid load generated by gfunc_return()"

tccgen.c:
- new function incr_offset(int) to increment a lvalue
- use it in gv/vstore to load/store from/to two-word types
- use it to advance the pointer to struct fields
- use it to load/store structs passed in registers
- structs: always assume that reg-classes of registers are 2^n
- adjust stack space when regsize > sizeof the_struct

x86_64-gen.c:
- return regsize=16 for VT_QLONG/QFLOAT

i386-gen.c:
- pass structs of size(8) as two VT_INT rather than one VT_LLONG
  (both should work now)

fixes a82aff3337
fixes fd6d2180c5 (slightly)

tests/tests2/131_return_struct_in_reg.c

@@ -1,49 +1,70 @@
 #include<stdio.h>
 
-#define DATA 0x1234567890abcdll, 0x5a5aa5a5f0f00f0fll
+struct s1 {
+    unsigned char a:4, b:4;
+} g1 = { 0x05, 0x0a };
 
-struct s {
-	long long int a;
-	long long int b;
-};
+struct s2 {
+    unsigned char a, b;
+} g2 = { 0x12, 0x34 };
 
-struct {
-	struct s d;
-} g = { { DATA } }, *gp = &g;
+struct s4 {
+    unsigned short a, b;
+} g4 = { 0x1245, 0x5678 };
 
-struct s
-foo1(void)
-{
-	struct s d = { DATA };
-	struct s *p = &d;
-	long long int x = 0;
-	return *p;
+struct s8 {
+    unsigned a, b;
+} g8 = { 0x12345678, 0x9abcdef0 };
+
+/* returned in 2 registers on riscv64 */
+struct s16 {
+    unsigned long long a, b;
+} g16 = { 0x123456789abcdef0ULL, 0xfedcba9876543210ULL };
+
+/* Homogeneous float aggregate on ARM hard-float */
+struct s_f4 {
+    double a, b, c, d;
+} g_f4 = { 1,2,3,4 };
+
+#define def(S) \
+struct s##S f##S(int x) \
+{ \
+    struct s##S l##S = g##S, *p##S = &l##S; \
+    if (x == 0) \
+        return g##S; \
+    else if (x == 1) \
+        return l##S; \
+    else \
+        return *p##S; \
 }
 
-struct s
-foo2(void)
-{
-	long long int unused = 0;
-	return gp->d;
-}
+def(1)
+def(2)
+def(4)
+def(8)
+def(16)
+def(_f4)
 
-struct s
-foo3(void)
-{
-	struct s d = { DATA };
-	long long int unused = 0;
-	return d;
-}
+#define chk(S,x) \
+    struct s##S l##S = f##S(x); \
+    printf("%02llx %02llx\n", \
+        (unsigned long long)l##S.a, \
+        (unsigned long long)l##S.b \
+        );
 
-int
-main(void)
+int main()
 {
-	struct s d;
-	d = foo1();
-	printf("%llx %llx\n", d.a, d.b);
-	d = foo2();
-	printf("%llx %llx\n", d.a, d.b);
-	d = foo3();
-	printf("%llx %llx\n", d.a, d.b);
-	return 0;
+    for (int x = 0;;) {
+        chk(1,x);
+        chk(2,x);
+        chk(4,x);
+        chk(8,x);
+        chk(16,x);
+        struct s_f4 l_f4 = f_f4(x);
+        printf("%.1f %.1f %.1f %.1f\n", l_f4.a, l_f4.b, l_f4.c, l_f4.d);
+        if (++x > 2)
+            break;
+        printf("\n");
+    }
+    return 0;
 }

tests/tests2/131_return_struct_in_reg.expect

@@ -1,3 +1,20 @@
-1234567890abcd 5a5aa5a5f0f00f0f
-1234567890abcd 5a5aa5a5f0f00f0f
-1234567890abcd 5a5aa5a5f0f00f0f
+05 0a
+12 34
+1245 5678
+12345678 9abcdef0
+123456789abcdef0 fedcba9876543210
+1.0 2.0 3.0 4.0
+
+05 0a
+12 34
+1245 5678
+12345678 9abcdef0
+123456789abcdef0 fedcba9876543210
+1.0 2.0 3.0 4.0
+
+05 0a
+12 34
+1245 5678
+12345678 9abcdef0
+123456789abcdef0 fedcba9876543210
+1.0 2.0 3.0 4.0