VLA fix: save stack pointer right after modification

This patch disables the optimization of saving stack pointers lazily,
which didn't fully take into account that control flow might not reach
the stack-saving instructions. I've decided to leave in the extra calls
to vla_sp_save() in case anyone wants to restore this optimization.

Tests added and enabled.

There are two remaining bugs: VLA variables can be modified, and jumping
into the scope of a declared VLA will cause a segfault rather than a
compiler error. Both of these do not affect correct C code, but should
be fixed at some point. Once VLA variables have been made properly
immutable, we can share them with the saved stack pointer and save stack
and instructions.

tccgen.c

@@ -3480,7 +3480,7 @@ static void post_type(CType *type, AttributeDef *ad)
 
             vla_runtime_type_size(type, &align);
             gen_op('*');
-            vset(&int_type, VT_LOCAL|VT_LVAL, loc);
+            vset(&int_type, VT_LOCAL|VT_LVAL, n);
             vswap();
             vstore();
         }
@@ -4809,7 +4809,7 @@ static void block(int *bsym, int *csym, int *case_sym, int *def_sym,
         gsym_addr(b, d);
     } else if (tok == '{') {
         Sym *llabel;
-        int block_vla_sp_loc, *saved_vla_sp_loc, saved_vla_flags;
+        int block_vla_sp_loc, *saved_vla_sp_loc, saved_vla_flags, *orig_vla_sp_loc;
 
         next();
         /* record local declaration stack position */
@@ -4822,7 +4822,8 @@ static void block(int *bsym, int *csym, int *case_sym, int *def_sym,
         /* save VLA state */
         block_vla_sp_loc = *(saved_vla_sp_loc = vla_sp_loc);
         if (saved_vla_sp_loc != &vla_sp_root_loc)
-          vla_sp_loc = &block_vla_sp_loc;
+            vla_sp_loc = &block_vla_sp_loc;
+        orig_vla_sp_loc = vla_sp_loc;
 
         saved_vla_flags = vla_flags;
         vla_flags |= VLA_NEED_NEW_FRAME;
@@ -4878,10 +4879,10 @@ static void block(int *bsym, int *csym, int *case_sym, int *def_sym,
         /* Pop VLA frames and restore stack pointer if required */
         if (saved_vla_sp_loc != &vla_sp_root_loc)
             *saved_vla_sp_loc = block_vla_sp_loc;
-        if (vla_sp_loc != (saved_vla_sp_loc == &vla_sp_root_loc ? &vla_sp_root_loc : &block_vla_sp_loc)) {
+        if (vla_sp_loc != orig_vla_sp_loc) {
-            vla_sp_loc = saved_vla_sp_loc;
+            gen_vla_sp_restore(*saved_vla_sp_loc);
-            gen_vla_sp_restore(*vla_sp_loc);
         }
+        vla_sp_loc = saved_vla_sp_loc;
         vla_flags = (vla_flags & ~VLA_SCOPE_FLAGS) | (saved_vla_flags & VLA_SCOPE_FLAGS);
         
         next();
@@ -5482,6 +5483,8 @@ static void decl_initializer(CType *type, Section *sec, unsigned long c,
         
         vla_runtime_type_size(type, &a);
         gen_vla_alloc(type, a);
+        vla_flags = VLA_IN_SCOPE;
+        vla_sp_save();
         vset(type, VT_LOCAL|VT_LVAL, c);
         vswap();
         vstore();

tests/tests2/79_vla_continue.c

@@ -81,12 +81,36 @@ void test4()
   }
 }
 
+void test5()
+{
+  int count = 10;
+  int a[f()];
+  int c[f()];
+
+  c[0] = 42;
+
+  for(;count--;) {
+    int b[f()];
+    int i;
+    for (i=0; i<f(); i++) {
+      b[i] = count;
+    }
+  }
+
+  if (c[0] == 42) {
+    printf("OK\n");
+  } else {
+    printf("NOT OK\n");
+  }
+}
+
 int main(void)
 {
   test1();
   test2();
   test3();
   test4();
+  test5();
 
   return 0;
 }

tests/tests2/79_vla_continue.expect

@@ -2,3 +2,4 @@ OK
 OK
 OK
 OK
+OK

tests/tests2/Makefile

@@ -96,9 +96,9 @@ TESTS =	\
  74_nocode_wanted.test \
  75_array_in_struct_init.test \
  76_dollars_in_identifiers.test \
- 77_push_pop_macro.test
+ 77_push_pop_macro.test \
-# 78_vla_label.test -- currently broken
+ 78_vla_label.test \
-# 79_vla_continue.test -- currently broken
+ 79_vla_continue.test
 
 # 34_array_assignment.test -- array assignment is not in C standard