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.

Philip committed 11 years ago

Commit 44c330d1 parent d2dd6fd4 files · +37 −9Browse files

Unified · Split

4 files

tccgen.c +9 −6
tests/tests2/79_vla_continue.c +24 −0
tests/tests2/79_vla_continue.expect +1 −0
tests/tests2/Makefile +3 −3

tccgen.c+9−6

             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();
         }
         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 */
         /* 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;
         /* 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();
         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+24−0

@@ -81,12 +81,36 @@ void test4() · 80 unmodified lines
81	}	81	}
82	}	82	}
83		83
		84	void test5()
		85	{
		86	int count = 10;
		87	int a[f()];
		88	int c[f()];
		89
		90	c[0] = 42;
		91
		92	for(;count--;) {
		93	int b[f()];
		94	int i;
		95	for (i=0; i<f(); i++) {
		96	b[i] = count;
		97	}
		98	}
		99
		100	if (c[0] == 42) {
		101	printf("OK\n");
		102	} else {
		103	printf("NOT OK\n");
		104	}
		105	}
		106
84	int main(void)	107	int main(void)
85	{	108	{
86	test1();	109	test1();
87	test2();	110	test2();
88	test3();	111	test3();
89	test4();	112	test4();
		113	test5();
90		114
91	return 0;	115	return 0;
92	}	116	}

tests/tests2/79_vla_continue.expect+1−0

@@ -2,3 +2,4 @@ OK · 1 unmodified line
2	OK	2	OK
3	OK	3	OK
4	OK	4	OK
		5	OK

tests/tests2/Makefile+3−3

@@ -96,9 +96,9 @@ TESTS = \ · 95 unmodified lines
96	74_nocode_wanted.test \	96	74_nocode_wanted.test \
97	75_array_in_struct_init.test \	97	75_array_in_struct_init.test \
98	76_dollars_in_identifiers.test \	98	76_dollars_in_identifiers.test \
99	77_push_pop_macro.test	99	77_push_pop_macro.test \
100	# 78_vla_label.test -- currently broken	100	78_vla_label.test \
101	# 79_vla_continue.test -- currently broken	101	79_vla_continue.test
102		102
103	# 34_array_assignment.test -- array assignment is not in C standard	103	# 34_array_assignment.test -- array assignment is not in C standard
104		104

VLA fix: save stack pointer right after modification

Keyboard shortcuts

General

Issues and pull requests

Issues, pull requests and Inbox

Repository code