Mikulas Patocka wrote:
Hi
The commit 7f1ab9b1e111b9ea9261eec4b7c6fb0f42591eef ("tccgen:
nodata_wanted") breaks tcc, it generates incorrect code where different
local variables are aliasing each other.
It can be tested with this program, if you compile it with broken tcc, it
prints "2".
#include
int main(void)
{
goto there;
if (0) {
int a, b;
there:
a = 1;
b = 2;
printf("%d\n", a);
}
return 0;
}
I think that that nodata_wanted misoptimization should be removed at all -
in the C language, you can jump to any location in the function with goto
or switch-case statement - thus reasoning such as "all the variables
behind if (0) are unreachable" is incorrect.
I see, right.
However NODATA_WANTED does more than that, for example it also suppresses
the "hello" with
if (0) puts("hello");
Therefor I'd suggest a less radical change, such as:
@@ -6916,7 +6916,7 @@ static void decl_initializer_alloc(CType *type,
AttributeDef *ad, int r,
align = 1;
}
-if (NODATA_WANTED)
+if (!v && NODATA_WANTED)
size = 0, align = 1;
if ((r & VT_VALMASK) == VT_LOCAL) {
Thus variable space will be allocated always but initializers are
still suppressed. (Bypassing initializers with goto is not allowed).
Btw, this one might fix the float problem from your previous mail:
@@ -882,9 +882,12 @@ void gfunc_call(int nb_args)
/* movq %xmm0, j*8(%rsp) */
gen_offs_sp(0xd60f66, 0x100, arg*8);
} else {
-/* movaps %xmm0, %xmmN */
-o(0x280f);
-o(0xc0 + (arg << 3));
+if (arg) {
+save_reg(TREG_XMM0 + arg);
+/* movaps %xmm0, %xmmN */
+o(0x280f);
+o(0xc0 + (arg << 3));
+}
d = arg_prepare_reg(arg);
/* mov %xmm0, %rxx */
o(0x66);
Thanks,
-- grischka
If you wanted to do that optimization correctly, you'd need to build
control flow graph, and tcc is just too simple to do that.
Mikulas
Signed-off-by: Mikulas Patocka
---
tccgen.c | 31 ---
tests/tests2/96_nodata_wanted.c | 56 ---
tests/tests2/96_nodata_wanted.expect | 11 --
3 files changed, 7 insertions(+), 91 deletions(-)
Index: tinycc/tccgen.c
===
--- tinycc.orig/tccgen.c2018-02-22 01:42:11.0 +0100
+++ tinycc/tccgen.c 2018-02-22 18:32:33.0 +0100
@@ -51,8 +51,7 @@ ST_DATA SValue __vstack[1+VSTACK_SIZE],
ST_DATA int const_wanted; /* true if constant wanted */
ST_DATA int nocode_wanted; /* no code generation wanted */
-#define NODATA_WANTED (nocode_wanted > 0) /* no static data output wanted
either */
-#define STATIC_DATA_WANTED (nocode_wanted & 0xC000) /* only static data
output */
+#define STATIC_DATA_WANTED (nocode_wanted & 0x8000) /* only static data
output */
ST_DATA int global_expr; /* true if compound literals must be allocated
globally (used during initializers parsing */
ST_DATA CType func_vt; /* current function return type (used by return
instruction) */
ST_DATA int func_var; /* true if current function is variadic (used by return
instruction) */
@@ -1296,8 +1295,6 @@ ST_FUNC int gv(int rc)
/* CPUs usually cannot use float constants, so we store them
generically in data segment */
size = type_size(>type, );
-if (NODATA_WANTED)
-size = 0, align = 1;
offset = section_add(data_section, size, align);
vpush_ref(>type, data_section, offset, size);
vswap();
@@ -4662,10 +4659,8 @@ ST_FUNC void unary(void)
type.t |= VT_ARRAY;
type.ref->c = len;
vpush_ref(, data_section, data_section->data_offset, len);
-if (!NODATA_WANTED) {
-ptr = section_ptr_add(data_section, len);
-memcpy(ptr, funcname, len);
-}
+ptr = section_ptr_add(data_section, len);
+memcpy(ptr, funcname, len);
next();
}
break;
@@ -6423,7 +6418,7 @@ static int decl_designator(CType *type,
vstore();
}
vpop();
-} else if (!NODATA_WANTED) {
+} else {
c_end = c + nb_elems * elem_size;
if (c_end > sec->data_allocated)
section_realloc(sec, c_end);
@@ -6467,11 +6462,6 @@ static void init_putv(CType *type, Secti
)
tcc_error("initializer element is not computable at load time");
-if (NODATA_WANTED) {
-vtop--;
-return;
-}
-
