Improved variable length array support.

VLA storage is now freed when it goes out of scope. This makes it
possible to use a VLA inside a loop without consuming an unlimited
amount of memory.

Combining VLAs with alloca() should work as in GCC - when a VLA is
freed, memory allocated by alloca() after the VLA was created is also
freed. There are some exceptions to this rule when using goto: if a VLA
is in scope at the goto, jumping to a label will reset the stack pointer
to where it was immediately after the last VLA was created prior to the
label, or to what it was before the first VLA was created if the label
is outside the scope of any VLA. This means that in some cases combining
alloca() and VLAs will free alloca() memory where GCC would not.

tcc.h

@@ -40,6 +40,13 @@
 #include <setjmp.h>
 #include <time.h>
 
+#ifdef CONFIG_TCCASSERT
+#include <assert.h>
+#define TCC_ASSERT(ex) assert(ex)
+#else
+#define TCC_ASSERT(ex)
+#endif
+
 #ifndef _WIN32
 # include <unistd.h>
 # include <sys/time.h>
@@ -404,6 +411,12 @@ typedef struct AttributeDef {
 #define SYM_FIELD      0x20000000 /* struct/union field symbol space */
 #define SYM_FIRST_ANOM 0x10000000 /* first anonymous sym */
 
+#define VLA_SP_LOC_SET     0x01 /* Location of SP on stack has been allocated */
+#define VLA_SP_SAVED       0x02 /* SP has been saved to slot already */
+#define VLA_NEED_NEW_FRAME 0x04 /* Needs new frame for next VLA */
+#define VLA_IN_SCOPE       0x08 /* One or more VLAs are in scope */
+#define VLA_SCOPE_FLAGS    (VLA_SP_SAVED|VLA_NEED_NEW_FRAME|VLA_IN_SCOPE) /* Flags which are saved and restored upon entering and exiting a block */
+
 /* stored in 'Sym.c' field */
 #define FUNC_NEW       1 /* ansi function prototype */
 #define FUNC_OLD       2 /* old function prototype */
@@ -1201,7 +1214,7 @@ ST_FUNC void decl(int l);
 #if defined CONFIG_TCC_BCHECK || defined TCC_TARGET_C67
 ST_FUNC Sym *get_sym_ref(CType *type, Section *sec, unsigned long offset, unsigned long size);
 #endif
-#ifdef TCC_TARGET_X86_64
+#if defined TCC_TARGET_X86_64 && !defined TCC_TARGET_PE
 ST_FUNC int classify_x86_64_va_arg(CType *ty);
 #endif
 
@@ -1286,6 +1299,9 @@ ST_FUNC void o(unsigned int c);
 #ifndef TCC_TARGET_ARM
 ST_FUNC void gen_cvt_itof(int t);
 #endif
+ST_FUNC void gen_vla_sp_save(int addr);
+ST_FUNC void gen_vla_sp_restore(int addr);
+ST_FUNC void gen_vla_alloc(CType *type, int align);
 
 /* ------------ i386-gen.c ------------ */
 #if defined TCC_TARGET_I386 || defined TCC_TARGET_X86_64