I don't think we need to change anything to get GCC behaviour, in that
case. alloca() doesn't need to call vla_sp_save because it has
different semantics from VLAs:
while(1) {
int *b = alloca(4);
}
will run out of memory eventually, while
while(1) {
int b[function_returning_1()];
printf("%p\n", b);
}
mustn't run out of memory. So, no, we shouldn't handle VLAs and
alloca() the same, because that would generate incorrect code in cases
like this:
int *p;
if (1) {
p = alloca(4);
}
*p = 0;
About the simplification patch: yes, it's specific to x86_64, should
have mentioned that. Fixed version attached.
(I've also started using the personal mob area at
http://repo.or.cz/w/tinycc.git/shortlog/refs/mob/mob_pipcet/simple-vlas,
which I think you can clone with
git config --add remote.origin.fetch
'+refs/mob/mob_pipcet/*:refs/remotes/origin/mob_pipcet/*'
git checkout origin/mob_pipcet/simple-vlas
I'm currently merging some of my other changes and they'll show up as
branches in that repository, if all goes well. Feel free to have a
look if you're curious.)
On Wed, Apr 29, 2015 at 5:05 AM, Sergey Korshunoff <[email protected]> wrote:
>> handle alloca like VLA regarding SP save/restore
> method 1: perform a call to the val_sp_save() analog from the alloca()
> method 2: define a built function alloca, which replace a call to the
> alloca with the VLA declaration. Is alloca*.S needed in such case?
>
> _______________________________________________
> Tinycc-devel mailing list
> [email protected]
> https://lists.nongnu.org/mailman/listinfo/tinycc-devel
diff --git a/i386-gen.c b/i386-gen.c
index b9dec83..a1ce4c5 100644
--- a/i386-gen.c
+++ b/i386-gen.c
@@ -1126,11 +1126,7 @@ ST_FUNC void gen_vla_alloc(CType *type, int align) {
/* We align to 16 bytes rather than align */
/* and ~15, %esp */
o(0xf0e483);
- /* mov %esp, r */
- o(0x89);
- o(0xe0 | r);
vpop();
- vset(type, r, 0);
#endif
}
diff --git a/tcc.h b/tcc.h
index 384e8de..f63d83c 100644
--- a/tcc.h
+++ b/tcc.h
@@ -464,12 +464,6 @@ typedef struct DLLReference {
#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 */
diff --git a/tccgen.c b/tccgen.c
index 8c1165f..9df285b 100644
--- a/tccgen.c
+++ b/tccgen.c
@@ -55,10 +55,9 @@ ST_DATA Sym *define_stack;
ST_DATA Sym *global_label_stack;
ST_DATA Sym *local_label_stack;
-ST_DATA int vla_sp_loc_tmp; /* vla_sp_loc is set to this when the value won't
be needed later */
+ST_DATA int vlas_in_scope; /* number of VLAs that are currently in scope */
ST_DATA int vla_sp_root_loc; /* vla_sp_loc for SP before any VLAs were pushed
*/
-ST_DATA int *vla_sp_loc; /* Pointer to variable holding location to store
stack pointer on the stack when modifying stack pointer */
-ST_DATA int vla_flags; /* VLA_* flags */
+ST_DATA int vla_sp_loc; /* Pointer to variable holding location to store stack
pointer on the stack when modifying stack pointer */
ST_DATA SValue __vstack[1+VSTACK_SIZE], *vtop;
@@ -87,7 +86,8 @@ static int decl0(int l, int is_for_loop_init);
static void expr_eq(void);
static void unary_type(CType *type);
static void vla_runtime_type_size(CType *type, int *a);
-static void vla_sp_save(void);
+static void vla_sp_restore(void);
+static void vla_sp_restore_root(void);
static int is_compatible_parameter_types(CType *type1, CType *type2);
static void expr_type(CType *type);
ST_FUNC void vpush64(int ty, unsigned long long v);
@@ -2223,14 +2223,15 @@ ST_FUNC void vla_runtime_type_size(CType *type, int *a)
}
}
-static void vla_sp_save(void) {
- if (!(vla_flags & VLA_SP_LOC_SET)) {
- *vla_sp_loc = (loc -= PTR_SIZE);
- vla_flags |= VLA_SP_LOC_SET;
+static void vla_sp_restore(void) {
+ if (vlas_in_scope) {
+ gen_vla_sp_restore(vla_sp_loc);
}
- if (!(vla_flags & VLA_SP_SAVED)) {
- gen_vla_sp_save(*vla_sp_loc);
- vla_flags |= VLA_SP_SAVED;
+}
+
+static void vla_sp_restore_root(void) {
+ if (vlas_in_scope) {
+ gen_vla_sp_restore(vla_sp_root_loc);
}
}
@@ -4794,10 +4795,7 @@ static void block(int *bsym, int *csym, int *case_sym,
int *def_sym,
} else if (tok == TOK_WHILE) {
next();
d = ind;
- if (vla_flags & VLA_IN_SCOPE) {
- gen_vla_sp_restore(*vla_sp_loc);
- vla_flags |= VLA_NEED_NEW_FRAME;
- }
+ vla_sp_restore();
skip('(');
gexpr();
skip(')');
@@ -4809,7 +4807,7 @@ 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,
*orig_vla_sp_loc;
+ int block_vla_sp_loc = vla_sp_loc, saved_vlas_in_scope = vlas_in_scope;
next();
/* record local declaration stack position */
@@ -4819,15 +4817,6 @@ static void block(int *bsym, int *csym, int *case_sym,
int *def_sym,
scope_stack_bottom = frame_bottom;
llabel = local_label_stack;
- /* 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;
- orig_vla_sp_loc = vla_sp_loc;
-
- saved_vla_flags = vla_flags;
- vla_flags |= VLA_NEED_NEW_FRAME;
-
/* handle local labels declarations */
if (tok == TOK_LABEL) {
next();
@@ -4877,13 +4866,11 @@ static void block(int *bsym, int *csym, int *case_sym,
int *def_sym,
sym_pop(&local_stack, s);
/* 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 != orig_vla_sp_loc) {
- gen_vla_sp_restore(*saved_vla_sp_loc);
+ if (vlas_in_scope > saved_vlas_in_scope) {
+ vla_sp_loc = saved_vlas_in_scope ? block_vla_sp_loc :
vla_sp_root_loc;
+ vla_sp_restore();
}
- vla_sp_loc = saved_vla_sp_loc;
- vla_flags = (vla_flags & ~VLA_SCOPE_FLAGS) | (saved_vla_flags &
VLA_SCOPE_FLAGS);
+ vlas_in_scope = saved_vlas_in_scope;
next();
} else if (tok == TOK_RETURN) {
@@ -4963,13 +4950,7 @@ static void block(int *bsym, int *csym, int *case_sym,
int *def_sym,
/* compute jump */
if (!csym)
tcc_error("cannot continue");
- if (vla_flags & VLA_IN_SCOPE) {
- /* If VLAs are in use, save the current stack pointer and
- reset the stack pointer to what it was at function entry
- (label will restore stack pointer in inner scopes) */
- vla_sp_save();
- gen_vla_sp_restore(vla_sp_root_loc);
- }
+ vla_sp_restore_root();
*csym = gjmp(*csym);
next();
skip(';');
@@ -4992,10 +4973,7 @@ static void block(int *bsym, int *csym, int *case_sym,
int *def_sym,
skip(';');
d = ind;
c = ind;
- if (vla_flags & VLA_IN_SCOPE) {
- gen_vla_sp_restore(*vla_sp_loc);
- vla_flags |= VLA_NEED_NEW_FRAME;
- }
+ vla_sp_restore();
a = 0;
b = 0;
if (tok != ';') {
@@ -5006,10 +4984,7 @@ static void block(int *bsym, int *csym, int *case_sym,
int *def_sym,
if (tok != ')') {
e = gjmp(0);
c = ind;
- if (vla_flags & VLA_IN_SCOPE) {
- gen_vla_sp_restore(*vla_sp_loc);
- vla_flags |= VLA_NEED_NEW_FRAME;
- }
+ vla_sp_restore();
gexpr();
vpop();
gjmp_addr(d);
@@ -5028,10 +5003,7 @@ static void block(int *bsym, int *csym, int *case_sym,
int *def_sym,
a = 0;
b = 0;
d = ind;
- if (vla_flags & VLA_IN_SCOPE) {
- gen_vla_sp_restore(*vla_sp_loc);
- vla_flags |= VLA_NEED_NEW_FRAME;
- }
+ vla_sp_restore();
block(&a, &b, case_sym, def_sym, case_reg, 0);
skip(TOK_WHILE);
skip('(');
@@ -5129,14 +5101,7 @@ static void block(int *bsym, int *csym, int *case_sym,
int *def_sym,
if (s->r == LABEL_DECLARED)
s->r = LABEL_FORWARD;
}
- /* label already defined */
- if (vla_flags & VLA_IN_SCOPE) {
- /* If VLAs are in use, save the current stack pointer and
- reset the stack pointer to what it was at function entry
- (label will restore stack pointer in inner scopes) */
- vla_sp_save();
- gen_vla_sp_restore(vla_sp_root_loc);
- }
+ vla_sp_restore_root();
if (s->r & LABEL_FORWARD)
s->jnext = gjmp(s->jnext);
else
@@ -5152,12 +5117,6 @@ static void block(int *bsym, int *csym, int *case_sym,
int *def_sym,
b = is_label();
if (b) {
/* label case */
- if (vla_flags & VLA_IN_SCOPE) {
- /* save/restore stack pointer across label
- this is a no-op when combined with the load immediately
- after the label unless we arrive via goto */
- vla_sp_save();
- }
s = label_find(b);
if (s) {
if (s->r == LABEL_DEFINED)
@@ -5168,10 +5127,7 @@ static void block(int *bsym, int *csym, int *case_sym,
int *def_sym,
s = label_push(&global_label_stack, b, LABEL_DEFINED);
}
s->jnext = ind;
- if (vla_flags & VLA_IN_SCOPE) {
- gen_vla_sp_restore(*vla_sp_loc);
- vla_flags |= VLA_NEED_NEW_FRAME;
- }
+ vla_sp_restore();
/* we accept this, but it is a mistake */
block_after_label:
if (tok == '}') {
@@ -5475,20 +5431,17 @@ static void decl_initializer(CType *type, Section *sec,
unsigned long c,
int a;
/* save current stack pointer */
- if (vla_flags & VLA_NEED_NEW_FRAME) {
- vla_sp_save();
- vla_flags = VLA_IN_SCOPE;
- vla_sp_loc = &vla_sp_loc_tmp;
+ if (vlas_in_scope == 0) {
+ if (vla_sp_root_loc == -1)
+ vla_sp_root_loc = (loc -= PTR_SIZE);
+ gen_vla_sp_save(vla_sp_root_loc);
}
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();
- vpop();
+ gen_vla_sp_save(c);
+ vla_sp_loc = c;
+ vlas_in_scope++;
} else if (type->t & VT_ARRAY) {
s = type->ref;
n = s->c;
@@ -6071,8 +6024,8 @@ static void gen_function(Sym *sym)
funcname = get_tok_str(sym->v, NULL);
func_ind = ind;
/* Initialize VLA state */
- vla_sp_loc = &vla_sp_root_loc;
- vla_flags = VLA_NEED_NEW_FRAME;
+ vla_sp_loc = -1;
+ vla_sp_root_loc = -1;
/* put debug symbol */
if (tcc_state->do_debug)
put_func_debug(sym);
diff --git a/x86_64-gen.c b/x86_64-gen.c
index c7a35d8..5a080af 100644
--- a/x86_64-gen.c
+++ b/x86_64-gen.c
@@ -2240,11 +2240,7 @@ ST_FUNC void gen_vla_alloc(CType *type, int align) {
/* We align to 16 bytes rather than align */
/* and ~15, %rsp */
o(0xf0e48348);
- /* mov %rsp, r */
- o(0x8948);
- o(0xe0 | REG_VALUE(r));
vpop();
- vset(type, r, 0);
#endif
}
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