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

@@ -3480,7 +3480,7 @@ static void post_type(CType type, AttributeDef ad) · 3479 unmodified lines
3480	3480
3481	3481	vla_runtime_type_size(type, &align);
3482	3482	gen_op('*');
3483		− vset(&int_type, VT_LOCAL\|VT_LVAL, loc);
	3483	+ vset(&int_type, VT_LOCAL\|VT_LVAL, n);
3484	3484	vswap();
3485	3485	vstore();
3486	3486	}
@@ -4809,7 +4809,7 @@ static void block(int bsym, int csym, int case_sym, int def_sym, · 1322 unmodified lines
4809	4809	gsym_addr(b, d);
4810	4810	} else if (tok == '{') {
4811	4811	Sym *llabel;
4812		− int block_vla_sp_loc, *saved_vla_sp_loc, saved_vla_flags;
	4812	+ int block_vla_sp_loc, saved_vla_sp_loc, saved_vla_flags, orig_vla_sp_loc;
4813	4813
4814	4814	next();
4815	4815	/* record local declaration stack position */
@@ -4822,7 +4822,8 @@ static void block(int bsym, int csym, int case_sym, int def_sym, · 6 unmodified lines
4822	4822	/* save VLA state */
4823	4823	block_vla_sp_loc = *(saved_vla_sp_loc = vla_sp_loc);
4824	4824	if (saved_vla_sp_loc != &vla_sp_root_loc)
4825		− vla_sp_loc = &block_vla_sp_loc;
	4825	+ vla_sp_loc = &block_vla_sp_loc;
	4826	+ orig_vla_sp_loc = vla_sp_loc;
4826	4827
4827	4828	saved_vla_flags = vla_flags;
4828	4829	vla_flags \|= VLA_NEED_NEW_FRAME;
@@ -4878,10 +4879,10 @@ static void block(int bsym, int csym, int case_sym, int def_sym, · 49 unmodified lines
4878	4879	/* Pop VLA frames and restore stack pointer if required */
4879	4880	if (saved_vla_sp_loc != &vla_sp_root_loc)
4880	4881	*saved_vla_sp_loc = block_vla_sp_loc;
4881		− if (vla_sp_loc != (saved_vla_sp_loc == &vla_sp_root_loc ? &vla_sp_root_loc : &block_vla_sp_loc)) {
4882		− vla_sp_loc = saved_vla_sp_loc;
4883		− gen_vla_sp_restore(*vla_sp_loc);
	4882	+ if (vla_sp_loc != orig_vla_sp_loc) {
	4883	+ gen_vla_sp_restore(*saved_vla_sp_loc);
4884	4884	}
	4885	+ vla_sp_loc = saved_vla_sp_loc;
4885	4886	vla_flags = (vla_flags & ~VLA_SCOPE_FLAGS) \| (saved_vla_flags & VLA_SCOPE_FLAGS);
4886	4887
4887	4888	next();
@@ -5482,6 +5483,8 @@ static void decl_initializer(CType type, Section sec, unsigned long c, · 594 unmodified lines
5482	5483
5483	5484	vla_runtime_type_size(type, &a);
5484	5485	gen_vla_alloc(type, a);
	5486	+ vla_flags = VLA_IN_SCOPE;
	5487	+ vla_sp_save();
5485	5488	vset(type, VT_LOCAL\|VT_LVAL, c);
5486	5489	vswap();
5487	5490	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	107	int main(void)
85	108	{
86	109	test1();
87	110	test2();
88	111	test3();
89	112	test4();
	113	+ test5();
90	114
91	115	return 0;
92	116	}

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

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

tests/tests2/Makefile+3−3

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

VLA fix: save stack pointer right after modification

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