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c++: Add __builtin_clear_padding builtin - C++20 P0528R3 compiler side [PR88101]

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The following patch implements __builtin_clear_padding builtin that clears
the padding bits in object representation (but preserves value
representation).  Inside of unions it clears only those padding bits that
are padding for all the union members (so that it never alters value
representation).

It handles trailing padding, padding in the middle of structs including
bitfields (PDP11 unhandled, I've never figured out how those bitfields
work), VLAs (doesn't handle variable length structures, but I think almost
nobody uses them and it isn't worth the extra complexity).  For VLAs and
sufficiently large arrays it uses runtime clearing loop instead of emitting
straight-line code (unless arrays are inside of a union).

The way I think this can be used for atomics is e.g. if the structures
are power of two sized and small enough that we use the hw atomics
for say compare_exchange __builtin_clear_padding could be called first on
the address of expected and desired arguments (for desired only if we want
to ensure that most of the time the atomic memory will have padding bits
cleared), then perform the weak cmpxchg and if that fails, we got the
value from the atomic memory; we can call __builtin_clear_padding on a copy
of that and then compare it with expected, and if it is the same with the
padding bits masked off, we can use the original with whatever random
padding bits in it as the new expected for next cmpxchg.
__builtin_clear_padding itself is not atomic and therefore it shouldn't
be called on the atomic memory itself, but compare_exchange*'s expected
argument is a reference and normally the implementation may store there
the current value from memory, so padding bits can be cleared in that,
and desired is passed by value rather than reference, so clearing is fine
too.
When using libatomic, we can use it either that way, or add new libatomic
APIs that accept another argument, pointer to the padding bit bitmask,
and construct that in the template as
  alignas (_T) unsigned char _mask[sizeof (_T)];
  std::memset (_mask, ~0, sizeof (_mask));
  __builtin_clear_padding ((_T *) _mask);
which will have bits cleared for padding bits and set for bits taking part
in the value representation.  Then libatomic could internally instead
of using memcmp compare
for (i = 0; i < N; i++) if ((val1[i] & mask[i]) != (val2[i] & mask[i]))

2020-11-20  Jakub Jelinek  <jakub@redhat.com>

	PR libstdc++/88101
gcc/
	* builtins.def (BUILT_IN_CLEAR_PADDING): New built-in function.
	* gimplify.c (gimplify_call_expr): Rewrite single argument
	BUILT_IN_CLEAR_PADDING into two-argument variant.
	* gimple-fold.c (clear_padding_unit, clear_padding_buf_size): New
	const variables.
	(struct clear_padding_struct): New type.
	(clear_padding_flush, clear_padding_add_padding,
	clear_padding_emit_loop, clear_padding_type,
	clear_padding_union, clear_padding_real_needs_padding_p,
	clear_padding_type_may_have_padding_p,
	gimple_fold_builtin_clear_padding): New functions.
	(gimple_fold_builtin): Handle BUILT_IN_CLEAR_PADDING.
	* doc/extend.texi (__builtin_clear_padding): Document.
gcc/c-family/
	* c-common.c (check_builtin_function_arguments): Handle
	BUILT_IN_CLEAR_PADDING.
gcc/testsuite/
	* c-c++-common/builtin-clear-padding-1.c: New test.
	* c-c++-common/torture/builtin-clear-padding-1.c: New test.
	* c-c++-common/torture/builtin-clear-padding-2.c: New test.
	* c-c++-common/torture/builtin-clear-padding-3.c: New test.
	* c-c++-common/torture/builtin-clear-padding-4.c: New test.
	* c-c++-common/torture/builtin-clear-padding-5.c: New test.
	* g++.dg/torture/builtin-clear-padding-1.C: New test.
	* g++.dg/torture/builtin-clear-padding-2.C: New test.
	* gcc.dg/builtin-clear-padding-1.c: New test.
This commit is contained in:
Jakub Jelinek 2020-11-20 12:28:34 +01:00
parent 410b8f6f41
commit 1bea0d0aa5
14 changed files with 1094 additions and 0 deletions
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1
gcc/builtins.def
View file

@ -839,6 +839,7 @@ DEF_EXT_LIB_BUILTIN (BUILT_IN_CLEAR_CACHE, "__clear_cache", BT_FN_VOID_PTR_PT
/* [trans-mem]: Adjust BUILT_IN_TM_CALLOC if BUILT_IN_CALLOC is changed. */
DEF_LIB_BUILTIN (BUILT_IN_CALLOC, "calloc", BT_FN_PTR_SIZE_SIZE, ATTR_MALLOC_WARN_UNUSED_RESULT_SIZE_1_2_NOTHROW_LEAF_LIST)
DEF_GCC_BUILTIN (BUILT_IN_CLASSIFY_TYPE, "classify_type", BT_FN_INT_VAR, ATTR_LEAF_LIST)
DEF_GCC_BUILTIN (BUILT_IN_CLEAR_PADDING, "clear_padding", BT_FN_VOID_VAR, ATTR_NOTHROW_NONNULL_TYPEGENERIC_LEAF)
DEF_GCC_BUILTIN (BUILT_IN_CLZ, "clz", BT_FN_INT_UINT, ATTR_CONST_NOTHROW_LEAF_LIST)
DEF_GCC_BUILTIN (BUILT_IN_CLZIMAX, "clzimax", BT_FN_INT_UINTMAX, ATTR_CONST_NOTHROW_LEAF_LIST)
DEF_GCC_BUILTIN (BUILT_IN_CLZL, "clzl", BT_FN_INT_ULONG, ATTR_CONST_NOTHROW_LEAF_LIST)

33
gcc/c-family/c-common.c
View file

@ -6178,6 +6178,39 @@ check_builtin_function_arguments (location_t loc, vec<location_t> arg_loc,
}
return false;
case BUILT_IN_CLEAR_PADDING:
if (builtin_function_validate_nargs (loc, fndecl, nargs, 1))
{
if (!POINTER_TYPE_P (TREE_TYPE (args[0])))
{
error_at (ARG_LOCATION (0), "argument %u in call to function "
"%qE does not have pointer type", 1, fndecl);
return false;
}
else if (!COMPLETE_TYPE_P (TREE_TYPE (TREE_TYPE (args[0]))))
{
error_at (ARG_LOCATION (0), "argument %u in call to function "
"%qE points to incomplete type", 1, fndecl);
return false;
}
else if (TYPE_READONLY (TREE_TYPE (TREE_TYPE (args[0]))))
{
error_at (ARG_LOCATION (0), "argument %u in call to function %qE "
"has pointer to %qs type (%qT)", 1, fndecl, "const",
TREE_TYPE (args[0]));
return false;
}
else if (TYPE_ATOMIC (TREE_TYPE (TREE_TYPE (args[0]))))
{
error_at (ARG_LOCATION (0), "argument %u in call to function %qE "
"has pointer to %qs type (%qT)", 1, fndecl,
"_Atomic", TREE_TYPE (args[0]));
return false;
}
return true;
}
return false;
default:
return true;
}

13
gcc/doc/extend.texi
View file

@ -13564,6 +13564,19 @@ initializers of variables usable in constant expressions. For more details
refer to the latest revision of the C++ standard.
@end deftypefn
@deftypefn {Built-in Function} void __builtin_clear_padding (@var{ptr})
The built-in function @code{__builtin_clear_padding} function clears
padding bits inside of the object representation of object pointed by
@var{ptr}, which has to be a pointer. The value representation of the
object is not affected. The type of the object is assumed to be the type
the pointer points to. Inside of a union, the only cleared bits are
bits that are padding bits for all the union members.
This built-in-function is useful if the padding bits of an object might
have intederminate values and the object representation needs to be
bitwise compared to some other object, for example for atomic operations.
@end deftypefn
@deftypefn {Built-in Function} long __builtin_expect (long @var{exp}, long @var{c})
@opindex fprofile-arcs
You may use @code{__builtin_expect} to provide the compiler with

695
gcc/gimple-fold.c
View file

@ -3948,6 +3948,698 @@ gimple_fold_builtin_realloc (gimple_stmt_iterator *gsi)
return false;
}
/* Number of bytes into which any type but aggregate or vector types
should fit. */
static constexpr size_t clear_padding_unit
= MAX_BITSIZE_MODE_ANY_MODE / BITS_PER_UNIT;
/* Buffer size on which __builtin_clear_padding folding code works. */
static const size_t clear_padding_buf_size = 32 * clear_padding_unit;
/* Data passed through __builtin_clear_padding folding. */
struct clear_padding_struct {
location_t loc;
tree base;
tree alias_type;
gimple_stmt_iterator *gsi;
/* Alignment of buf->base + 0. */
unsigned align;
/* Offset from buf->base. Should be always a multiple of UNITS_PER_WORD. */
HOST_WIDE_INT off;
/* Number of padding bytes before buf->off that don't have padding clear
code emitted yet. */
HOST_WIDE_INT padding_bytes;
/* The size of the whole object. Never emit code to touch
buf->base + buf->sz or following bytes. */
HOST_WIDE_INT sz;
/* Number of bytes recorded in buf->buf. */
size_t size;
/* When inside union, instead of emitting code we and bits inside of
the union_ptr array. */
unsigned char *union_ptr;
/* Set bits mean padding bits that need to be cleared by the builtin. */
unsigned char buf[clear_padding_buf_size + clear_padding_unit];
};
/* Emit code to clear padding requested in BUF->buf - set bits
in there stand for padding that should be cleared. FULL is true
if everything from the buffer should be flushed, otherwise
it can leave up to 2 * clear_padding_unit bytes for further
processing. */
static void
clear_padding_flush (clear_padding_struct *buf, bool full)
{
gcc_assert ((clear_padding_unit % UNITS_PER_WORD) == 0);
if (!full && buf->size < 2 * clear_padding_unit)
return;
gcc_assert ((buf->off % UNITS_PER_WORD) == 0);
size_t end = buf->size;
if (!full)
end = ((end - clear_padding_unit - 1) / clear_padding_unit
* clear_padding_unit);
size_t padding_bytes = buf->padding_bytes;
if (buf->union_ptr)
{
/* Inside of a union, instead of emitting any code, instead
clear all bits in the union_ptr buffer that are clear
in buf. Whole padding bytes don't clear anything. */
for (size_t i = 0; i < end; i++)
{
if (buf->buf[i] == (unsigned char) ~0)
padding_bytes++;
else
{
padding_bytes = 0;
buf->union_ptr[buf->off + i] &= buf->buf[i];
}
}
if (full)
{
buf->off = 0;
buf->size = 0;
buf->padding_bytes = 0;
}
else
{
memmove (buf->buf, buf->buf + end, buf->size - end);
buf->off += end;
buf->size -= end;
buf->padding_bytes = padding_bytes;
}
return;
}
size_t wordsize = UNITS_PER_WORD;
for (size_t i = 0; i < end; i += wordsize)
{
size_t nonzero_first = wordsize;
size_t nonzero_last = 0;
bool all_ones = true;
if ((unsigned HOST_WIDE_INT) (buf->off + i + wordsize)
> (unsigned HOST_WIDE_INT) buf->sz)
{
gcc_assert (wordsize > 1);
wordsize /= 2;
i -= wordsize;
continue;
}
for (size_t j = i; j < i + wordsize && j < end; j++)
{
if (buf->buf[j])
{
if (nonzero_first == wordsize)
{
nonzero_first = j - i;
nonzero_last = j - i;
}
if (nonzero_last != j - i)
all_ones = false;
nonzero_last = j + 1 - i;
}
if (buf->buf[j] != 0 && buf->buf[j] != (unsigned char) ~0)
all_ones = false;
}
if (padding_bytes)
{
if (nonzero_first == 0
&& nonzero_last == wordsize
&& all_ones)
{
/* All bits are padding and we had some padding
before too. Just extend it. */
padding_bytes += wordsize;
continue;
}
size_t padding_end = i;
if (all_ones && nonzero_first == 0)
{
padding_bytes += nonzero_last;
padding_end += nonzero_last;
nonzero_first = wordsize;
nonzero_last = 0;
}
tree atype = build_array_type_nelts (char_type_node, padding_bytes);
tree dst = build2_loc (buf->loc, MEM_REF, atype, buf->base,
build_int_cst (buf->alias_type,
buf->off + padding_end
- padding_bytes));
tree src = build_constructor (atype, NULL);
gimple *g = gimple_build_assign (dst, src);
gimple_set_location (g, buf->loc);
gsi_insert_before (buf->gsi, g, GSI_SAME_STMT);
padding_bytes = 0;
buf->padding_bytes = 0;
}
if (nonzero_first == wordsize)
/* All bits in a word are 0, there are no padding bits. */
continue;
if (all_ones && nonzero_last == wordsize)
{
/* All bits between nonzero_first and end of word are padding
bits, start counting padding_bytes. */
padding_bytes = nonzero_last - nonzero_first;
continue;
}
for (size_t eltsz = 1; eltsz <= wordsize; eltsz <<= 1)
{
if (nonzero_last - nonzero_first <= eltsz
&& ((nonzero_first & ~(eltsz - 1))
== ((nonzero_last - 1) & ~(eltsz - 1))))
{
tree type;
if (eltsz == 1)
type = char_type_node;
else
type = lang_hooks.types.type_for_size (eltsz * BITS_PER_UNIT,
0);
size_t start = nonzero_first & ~(eltsz - 1);
HOST_WIDE_INT off = buf->off + i + start;
tree atype = type;
if (eltsz > 1 && buf->align < TYPE_ALIGN (type))
atype = build_aligned_type (type, buf->align);
tree dst = build2_loc (buf->loc, MEM_REF, atype, buf->base,
build_int_cst (buf->alias_type, off));
tree src;
gimple *g;
if (all_ones
&& nonzero_first == start
&& nonzero_last == start + eltsz)
src = build_zero_cst (type);
else
{
src = make_ssa_name (type);
g = gimple_build_assign (src, unshare_expr (dst));
gimple_set_location (g, buf->loc);
gsi_insert_before (buf->gsi, g, GSI_SAME_STMT);
tree mask = native_interpret_expr (type,
buf->buf + i + start,
eltsz);
gcc_assert (mask && TREE_CODE (mask) == INTEGER_CST);
mask = fold_build1 (BIT_NOT_EXPR, type, mask);
tree src_masked = make_ssa_name (type);
g = gimple_build_assign (src_masked, BIT_AND_EXPR,
src, mask);
gimple_set_location (g, buf->loc);
gsi_insert_before (buf->gsi, g, GSI_SAME_STMT);
src = src_masked;
}
g = gimple_build_assign (dst, src);
gimple_set_location (g, buf->loc);
gsi_insert_before (buf->gsi, g, GSI_SAME_STMT);
break;
}
}
}
if (full)
{
if (padding_bytes)
{
tree atype = build_array_type_nelts (char_type_node, padding_bytes);
tree dst = build2_loc (buf->loc, MEM_REF, atype, buf->base,
build_int_cst (buf->alias_type,
buf->off + end
- padding_bytes));
tree src = build_constructor (atype, NULL);
gimple *g = gimple_build_assign (dst, src);
gimple_set_location (g, buf->loc);
gsi_insert_before (buf->gsi, g, GSI_SAME_STMT);
}
size_t end_rem = end % UNITS_PER_WORD;
buf->off += end - end_rem;
buf->size = end_rem;
memset (buf->buf, 0, buf->size);
buf->padding_bytes = 0;
}
else
{
memmove (buf->buf, buf->buf + end, buf->size - end);
buf->off += end;
buf->size -= end;
buf->padding_bytes = padding_bytes;
}
}
/* Append PADDING_BYTES padding bytes. */
static void
clear_padding_add_padding (clear_padding_struct *buf,
HOST_WIDE_INT padding_bytes)
{
if (padding_bytes == 0)
return;
if ((unsigned HOST_WIDE_INT) padding_bytes + buf->size
> (unsigned HOST_WIDE_INT) clear_padding_buf_size)
clear_padding_flush (buf, false);
if ((unsigned HOST_WIDE_INT) padding_bytes + buf->size
> (unsigned HOST_WIDE_INT) clear_padding_buf_size)
{
memset (buf->buf + buf->size, ~0, clear_padding_buf_size - buf->size);
padding_bytes -= clear_padding_buf_size - buf->size;
buf->size = clear_padding_buf_size;
clear_padding_flush (buf, false);
gcc_assert (buf->padding_bytes);
/* At this point buf->buf[0] through buf->buf[buf->size - 1]
is guaranteed to be all ones. */
padding_bytes += buf->size;
buf->size = padding_bytes % UNITS_PER_WORD;
memset (buf->buf, ~0, buf->size);
buf->off += padding_bytes - buf->size;
buf->padding_bytes += padding_bytes - buf->size;
}
else
{
memset (buf->buf + buf->size, ~0, padding_bytes);
buf->size += padding_bytes;
}
}
static void clear_padding_type (clear_padding_struct *, tree, HOST_WIDE_INT);
/* Clear padding bits of union type TYPE. */
static void
clear_padding_union (clear_padding_struct *buf, tree type, HOST_WIDE_INT sz)
{
clear_padding_struct *union_buf;
HOST_WIDE_INT start_off = 0, next_off = 0;
size_t start_size = 0;
if (buf->union_ptr)
{
start_off = buf->off + buf->size;
next_off = start_off + sz;
start_size = start_off % UNITS_PER_WORD;
start_off -= start_size;
clear_padding_flush (buf, true);
union_buf = buf;
}
else
{
if (sz + buf->size > clear_padding_buf_size)
clear_padding_flush (buf, false);
union_buf = XALLOCA (clear_padding_struct);
union_buf->loc = buf->loc;
union_buf->base = NULL_TREE;
union_buf->alias_type = NULL_TREE;
union_buf->gsi = NULL;
union_buf->align = 0;
union_buf->off = 0;
union_buf->padding_bytes = 0;
union_buf->sz = sz;
union_buf->size = 0;
if (sz + buf->size <= clear_padding_buf_size)
union_buf->union_ptr = buf->buf + buf->size;
else
union_buf->union_ptr = XNEWVEC (unsigned char, sz);
memset (union_buf->union_ptr, ~0, sz);
}
for (tree field = TYPE_FIELDS (type); field; field = DECL_CHAIN (field))
if (TREE_CODE (field) == FIELD_DECL)
{
HOST_WIDE_INT fldsz = tree_to_shwi (DECL_SIZE_UNIT (field));
gcc_assert (union_buf->size == 0);
union_buf->off = start_off;
union_buf->size = start_size;
memset (union_buf->buf, ~0, start_size);
clear_padding_type (union_buf, TREE_TYPE (field), fldsz);
clear_padding_add_padding (union_buf, sz - fldsz);
clear_padding_flush (union_buf, true);
}
if (buf == union_buf)
{
buf->off = next_off;
buf->size = next_off % UNITS_PER_WORD;
buf->off -= buf->size;
memset (buf->buf, ~0, buf->size);
}
else if (sz + buf->size <= clear_padding_buf_size)
buf->size += sz;
else
{
unsigned char *union_ptr = union_buf->union_ptr;
while (sz)
{
clear_padding_flush (buf, false);
HOST_WIDE_INT this_sz
= MIN ((unsigned HOST_WIDE_INT) sz,
clear_padding_buf_size - buf->size);
memcpy (buf->buf + buf->size, union_ptr, this_sz);
buf->size += this_sz;
union_ptr += this_sz;
sz -= this_sz;
}
XDELETE (union_buf->union_ptr);
}
}
/* The only known floating point formats with padding bits are the
IEEE extended ones. */
static bool
clear_padding_real_needs_padding_p (tree type)
{
const struct real_format *fmt = REAL_MODE_FORMAT (TYPE_MODE (type));
return (fmt->b == 2
&& fmt->signbit_ro == fmt->signbit_rw
&& (fmt->signbit_ro == 79 || fmt->signbit_ro == 95));
}
/* Return true if TYPE might contain any padding bits. */
static bool
clear_padding_type_may_have_padding_p (tree type)
{
switch (TREE_CODE (type))
{
case RECORD_TYPE:
case UNION_TYPE:
return true;
case ARRAY_TYPE:
case COMPLEX_TYPE:
case VECTOR_TYPE:
return clear_padding_type_may_have_padding_p (TREE_TYPE (type));
case REAL_TYPE:
return clear_padding_real_needs_padding_p (type);
default:
return false;
}
}
/* Emit a runtime loop:
for (; buf.base != end; buf.base += sz)
__builtin_clear_padding (buf.base); */
static void
clear_padding_emit_loop (clear_padding_struct *buf, tree type, tree end)
{
tree l1 = create_artificial_label (buf->loc);
tree l2 = create_artificial_label (buf->loc);
tree l3 = create_artificial_label (buf->loc);
gimple *g = gimple_build_goto (l2);
gimple_set_location (g, buf->loc);
gsi_insert_before (buf->gsi, g, GSI_SAME_STMT);
g = gimple_build_label (l1);
gimple_set_location (g, buf->loc);
gsi_insert_before (buf->gsi, g, GSI_SAME_STMT);
clear_padding_type (buf, type, buf->sz);
clear_padding_flush (buf, true);
g = gimple_build_assign (buf->base, POINTER_PLUS_EXPR, buf->base,
size_int (buf->sz));
gimple_set_location (g, buf->loc);
gsi_insert_before (buf->gsi, g, GSI_SAME_STMT);
g = gimple_build_label (l2);
gimple_set_location (g, buf->loc);
gsi_insert_before (buf->gsi, g, GSI_SAME_STMT);
g = gimple_build_cond (NE_EXPR, buf->base, end, l1, l3);
gimple_set_location (g, buf->loc);
gsi_insert_before (buf->gsi, g, GSI_SAME_STMT);
g = gimple_build_label (l3);
gimple_set_location (g, buf->loc);
gsi_insert_before (buf->gsi, g, GSI_SAME_STMT);
}
/* Clear padding bits for TYPE. Called recursively from
gimple_fold_builtin_clear_padding. */
static void
clear_padding_type (clear_padding_struct *buf, tree type, HOST_WIDE_INT sz)
{
switch (TREE_CODE (type))
{
case RECORD_TYPE:
HOST_WIDE_INT cur_pos;
cur_pos = 0;
for (tree field = TYPE_FIELDS (type); field; field = DECL_CHAIN (field))
if (TREE_CODE (field) == FIELD_DECL)
{
if (DECL_BIT_FIELD (field))
{
if (DECL_NAME (field) == NULL_TREE)
continue;
HOST_WIDE_INT fldsz = TYPE_PRECISION (TREE_TYPE (field));
if (fldsz == 0)
continue;
HOST_WIDE_INT pos = int_byte_position (field);
HOST_WIDE_INT bpos
= tree_to_uhwi (DECL_FIELD_BIT_OFFSET (field));
bpos %= BITS_PER_UNIT;
HOST_WIDE_INT end
= ROUND_UP (bpos + fldsz, BITS_PER_UNIT) / BITS_PER_UNIT;
if (pos + end > cur_pos)
{
clear_padding_add_padding (buf, pos + end - cur_pos);
cur_pos = pos + end;
}
gcc_assert (cur_pos > pos
&& ((unsigned HOST_WIDE_INT) buf->size
>= (unsigned HOST_WIDE_INT) cur_pos - pos));
unsigned char *p = buf->buf + buf->size - (cur_pos - pos);
if (BYTES_BIG_ENDIAN != WORDS_BIG_ENDIAN)
sorry_at (buf->loc, "PDP11 bit-field handling unsupported"
" in %qs", "__builtin_clear_padding");
else if (BYTES_BIG_ENDIAN)
{
/* Big endian. */
if (bpos + fldsz <= BITS_PER_UNIT)
*p &= ~(((1 << fldsz) - 1)
<< (BITS_PER_UNIT - bpos - fldsz));
else
{
if (bpos)
{
*p &= ~(((1U << BITS_PER_UNIT) - 1) >> bpos);
p++;
fldsz -= BITS_PER_UNIT - bpos;
}
memset (p, 0, fldsz / BITS_PER_UNIT);
p += fldsz / BITS_PER_UNIT;
fldsz %= BITS_PER_UNIT;
if (fldsz)
*p &= ((1U << BITS_PER_UNIT) - 1) >> fldsz;
}
}
else
{
/* Little endian. */
if (bpos + fldsz <= BITS_PER_UNIT)
*p &= ~(((1 << fldsz) - 1) << bpos);
else
{
if (bpos)
{
*p &= ~(((1 << BITS_PER_UNIT) - 1) << bpos);
p++;
fldsz -= BITS_PER_UNIT - bpos;
}
memset (p, 0, fldsz / BITS_PER_UNIT);
p += fldsz / BITS_PER_UNIT;
fldsz %= BITS_PER_UNIT;
if (fldsz)
*p &= ~((1 << fldsz) - 1);
}
}
}
else
{
HOST_WIDE_INT pos = int_byte_position (field);
HOST_WIDE_INT fldsz = tree_to_shwi (DECL_SIZE_UNIT (field));
gcc_assert (pos >= 0 && fldsz >= 0 && pos >= cur_pos);
clear_padding_add_padding (buf, pos - cur_pos);
cur_pos = pos;
clear_padding_type (buf, TREE_TYPE (field), fldsz);
cur_pos += fldsz;
}
}
gcc_assert (sz >= cur_pos);
clear_padding_add_padding (buf, sz - cur_pos);
break;
case ARRAY_TYPE:
HOST_WIDE_INT nelts, fldsz;
fldsz = int_size_in_bytes (TREE_TYPE (type));
nelts = sz / fldsz;
if (nelts > 1
&& sz > 8 * UNITS_PER_WORD
&& buf->union_ptr == NULL
&& clear_padding_type_may_have_padding_p (TREE_TYPE (type)))
{
/* For sufficiently large array of more than one elements,
emit a runtime loop to keep code size manageable. */
tree base = buf->base;
unsigned int prev_align = buf->align;
HOST_WIDE_INT off = buf->off + buf->size;
HOST_WIDE_INT prev_sz = buf->sz;
clear_padding_flush (buf, true);
tree elttype = TREE_TYPE (type);
buf->base = create_tmp_var (build_pointer_type (elttype));
tree end = make_ssa_name (TREE_TYPE (buf->base));
gimple *g = gimple_build_assign (buf->base, POINTER_PLUS_EXPR,
base, size_int (off));
gimple_set_location (g, buf->loc);
gsi_insert_before (buf->gsi, g, GSI_SAME_STMT);
g = gimple_build_assign (end, POINTER_PLUS_EXPR, buf->base,
size_int (sz));
gimple_set_location (g, buf->loc);
gsi_insert_before (buf->gsi, g, GSI_SAME_STMT);
buf->sz = fldsz;
buf->align = TYPE_ALIGN (elttype);
buf->off = 0;
buf->size = 0;
clear_padding_emit_loop (buf, elttype, end);
buf->base = base;
buf->sz = prev_sz;
buf->align = prev_align;
buf->size = off % UNITS_PER_WORD;
buf->off = off - buf->size;
memset (buf->buf, 0, buf->size);
break;
}
for (HOST_WIDE_INT i = 0; i < nelts; i++)
clear_padding_type (buf, TREE_TYPE (type), fldsz);
break;
case UNION_TYPE:
clear_padding_union (buf, type, sz);
break;
case REAL_TYPE:
gcc_assert ((size_t) sz <= clear_padding_unit);
if ((unsigned HOST_WIDE_INT) sz + buf->size > clear_padding_buf_size)
clear_padding_flush (buf, false);
if (clear_padding_real_needs_padding_p (type))
{
/* Use native_interpret_expr + native_encode_expr to figure out
which bits are padding. */
memset (buf->buf + buf->size, ~0, sz);
tree cst = native_interpret_expr (type, buf->buf + buf->size, sz);
gcc_assert (cst && TREE_CODE (cst) == REAL_CST);
int len = native_encode_expr (cst, buf->buf + buf->size, sz);
gcc_assert (len > 0 && (size_t) len == (size_t) sz);
for (size_t i = 0; i < (size_t) sz; i++)
buf->buf[buf->size + i] ^= ~0;
}
else
memset (buf->buf + buf->size, 0, sz);
buf->size += sz;
break;
case COMPLEX_TYPE:
fldsz = int_size_in_bytes (TREE_TYPE (type));
clear_padding_type (buf, TREE_TYPE (type), fldsz);
clear_padding_type (buf, TREE_TYPE (type), fldsz);
break;
case VECTOR_TYPE:
nelts = TYPE_VECTOR_SUBPARTS (type).to_constant ();
fldsz = int_size_in_bytes (TREE_TYPE (type));
for (HOST_WIDE_INT i = 0; i < nelts; i++)
clear_padding_type (buf, TREE_TYPE (type), fldsz);
break;
case NULLPTR_TYPE:
gcc_assert ((size_t) sz <= clear_padding_unit);
if ((unsigned HOST_WIDE_INT) sz + buf->size > clear_padding_buf_size)
clear_padding_flush (buf, false);
memset (buf->buf + buf->size, ~0, sz);
buf->size += sz;
break;
default:
gcc_assert ((size_t) sz <= clear_padding_unit);
if ((unsigned HOST_WIDE_INT) sz + buf->size > clear_padding_buf_size)
clear_padding_flush (buf, false);
memset (buf->buf + buf->size, 0, sz);
buf->size += sz;
break;
}
}
/* Fold __builtin_clear_padding builtin. */
static bool
gimple_fold_builtin_clear_padding (gimple_stmt_iterator *gsi)
{
gimple *stmt = gsi_stmt (*gsi);
gcc_assert (gimple_call_num_args (stmt) == 2);
tree ptr = gimple_call_arg (stmt, 0);
tree typearg = gimple_call_arg (stmt, 1);
tree type = TREE_TYPE (TREE_TYPE (typearg));
location_t loc = gimple_location (stmt);
clear_padding_struct buf;
gimple_stmt_iterator gsiprev = *gsi;
/* This should be folded during the lower pass. */
gcc_assert (!gimple_in_ssa_p (cfun) && cfun->cfg == NULL);
gcc_assert (COMPLETE_TYPE_P (type));
gsi_prev (&gsiprev);
buf.loc = loc;
buf.base = ptr;
buf.alias_type = NULL_TREE;
buf.gsi = gsi;
buf.align = get_pointer_alignment (ptr);
unsigned int talign = min_align_of_type (type) * BITS_PER_UNIT;
buf.align = MAX (buf.align, talign);
buf.off = 0;
buf.padding_bytes = 0;
buf.size = 0;
buf.sz = int_size_in_bytes (type);
buf.union_ptr = NULL;
if (buf.sz < 0 && int_size_in_bytes (strip_array_types (type)) < 0)
sorry_at (loc, "%s not supported for variable length aggregates",
"__builtin_clear_padding");
/* The implementation currently assumes 8-bit host and target
chars which is the case for all currently supported targets
and hosts and is required e.g. for native_{encode,interpret}* APIs. */
else if (CHAR_BIT != 8 || BITS_PER_UNIT != 8)
sorry_at (loc, "%s not supported on this target",
"__builtin_clear_padding");
else if (!clear_padding_type_may_have_padding_p (type))
;
else if (TREE_CODE (type) == ARRAY_TYPE && buf.sz < 0)
{
tree sz = TYPE_SIZE_UNIT (type);
tree elttype = type;
/* Only supports C/C++ VLAs and flattens all the VLA levels. */
while (TREE_CODE (elttype) == ARRAY_TYPE
&& int_size_in_bytes (elttype) < 0)
elttype = TREE_TYPE (elttype);
HOST_WIDE_INT eltsz = int_size_in_bytes (elttype);
gcc_assert (eltsz >= 0);
if (eltsz)
{
buf.base = create_tmp_var (build_pointer_type (elttype));
tree end = make_ssa_name (TREE_TYPE (buf.base));
gimple *g = gimple_build_assign (buf.base, ptr);
gimple_set_location (g, loc);
gsi_insert_before (gsi, g, GSI_SAME_STMT);
g = gimple_build_assign (end, POINTER_PLUS_EXPR, buf.base, sz);
gimple_set_location (g, loc);
gsi_insert_before (gsi, g, GSI_SAME_STMT);
buf.sz = eltsz;
buf.align = TYPE_ALIGN (elttype);
buf.alias_type = build_pointer_type (elttype);
clear_padding_emit_loop (&buf, elttype, end);
}
}
else
{
if (!is_gimple_mem_ref_addr (buf.base))
{
buf.base = make_ssa_name (TREE_TYPE (ptr));
gimple *g = gimple_build_assign (buf.base, ptr);
gimple_set_location (g, loc);
gsi_insert_before (gsi, g, GSI_SAME_STMT);
}
buf.alias_type = build_pointer_type (type);
clear_padding_type (&buf, type, buf.sz);
clear_padding_flush (&buf, true);
}
gimple_stmt_iterator gsiprev2 = *gsi;
gsi_prev (&gsiprev2);
if (gsi_stmt (gsiprev) == gsi_stmt (gsiprev2))
gsi_replace (gsi, gimple_build_nop (), true);
else
{
gsi_remove (gsi, true);
*gsi = gsiprev2;
}
return true;
}
/* Fold the non-target builtin at *GSI and return whether any simplification
was made. */
@ -4105,6 +4797,9 @@ gimple_fold_builtin (gimple_stmt_iterator *gsi)
case BUILT_IN_REALLOC:
return gimple_fold_builtin_realloc (gsi);
case BUILT_IN_CLEAR_PADDING:
return gimple_fold_builtin_clear_padding (gsi);
default:;
}

14
gcc/gimplify.c
View file

@ -3384,6 +3384,20 @@ gimplify_call_expr (tree *expr_p, gimple_seq *pre_p, bool want_value)
cfun->calls_eh_return = true;
break;
case BUILT_IN_CLEAR_PADDING:
if (call_expr_nargs (*expr_p) == 1)
{
/* Remember the original type of the argument in an internal
dummy second argument, as in GIMPLE pointer conversions are
useless. */
p = CALL_EXPR_ARG (*expr_p, 0);
*expr_p
= build_call_expr_loc (EXPR_LOCATION (*expr_p), fndecl, 2, p,
build_zero_cst (TREE_TYPE (p)));
return GS_OK;
}
break;
default:
;
}

19
gcc/testsuite/c-c++-common/builtin-clear-padding-1.c Normal file
View file

@ -0,0 +1,19 @@
/* PR libstdc++/88101 */
/* { dg-do compile } */
struct S;
struct T { char a; long long b; };
void
foo (struct S *p, void *q, char *r, const struct T *s)
{
__builtin_clear_padding (); /* { dg-error "too few arguments to function '__builtin_clear_padding'" } */
__builtin_clear_padding (1); /* { dg-error "argument 1 in call to function '__builtin_clear_padding' does not have pointer type" } */
__builtin_clear_padding (&p);
__builtin_clear_padding (&p, 1); /* { dg-error "too many arguments to function '__builtin_clear_padding'" } */
__builtin_clear_padding (&p, &p); /* { dg-error "too many arguments to function '__builtin_clear_padding'" } */
__builtin_clear_padding (p); /* { dg-error "argument 1 in call to function '__builtin_clear_padding' points to incomplete type" } */
__builtin_clear_padding (q); /* { dg-error "argument 1 in call to function '__builtin_clear_padding' points to incomplete type" } */
__builtin_clear_padding (r);
__builtin_clear_padding (s); /* { dg-error "argument 1 in call to function '__builtin_clear_padding' has pointer to 'const' type" } */
}

47
gcc/testsuite/c-c++-common/torture/builtin-clear-padding-1.c Normal file
View file

@ -0,0 +1,47 @@
/* PR libstdc++/88101 */
int i1, i2;
long double l1, l2;
struct S { char a; short b; char c; int d; char e; long long f; char g; long double h; } s1, s2;
struct T { int a; struct S b[3]; int c; } t1, t2;
struct U { int a : 3; int : 2; int b : 15; int : 14; int c : 1; int : 0; int : 3; int d : 2; int : 3; int e : 13; int : 3; signed char f; } u1, u2;
__attribute__((noipa)) void
foo (int *i, long double *l, struct S *s, struct T *t, struct U *u)
{
*i = 123;
*l = -123.456L;
s->a = 1; s->b = 2; s->c = 3; s->d = 4; s->e = 5; s->f = 6; s->g = 7; s->h = 18.52L;
t->a = 8; t->c = 9;
t->b[0].a = 11; t->b[0].b = 12; t->b[0].c = 13; t->b[0].d = 14;
t->b[0].e = 15; t->b[0].f = 16; t->b[0].g = 17; t->b[0].h = 18.26L;
t->b[1].a = 21; t->b[1].b = 22; t->b[1].c = 23; t->b[1].d = 24;
t->b[1].e = 25; t->b[1].f = 26; t->b[1].g = 27; t->b[1].h = 28.26L;
t->b[2].a = 31; t->b[2].b = 32; t->b[2].c = 33; t->b[2].d = 34;
t->b[2].e = 35; t->b[2].f = 36; t->b[2].g = 37; t->b[2].h = 38.26L;
u->a = -1; u->b = -1; u->c = -1; u->d = -1; u->e = -1; u->f = -1;
}
int
main ()
{
__builtin_memset (&i2, -1, sizeof (i2));
__builtin_memset (&l2, -1, sizeof (i2));
__builtin_memset (&s2, -1, sizeof (s2));
__builtin_memset (&t2, -1, sizeof (t2));
__builtin_memset (&u2, -1, sizeof (u2));
foo (&i1, &l1, &s1, &t1, &u1);
foo (&i2, &l2, &s2, &t2, &u2);
__builtin_clear_padding (&i2);
__builtin_clear_padding (&l2);
__builtin_clear_padding (&s2);
__builtin_clear_padding (&t2);
__builtin_clear_padding (&u2);
if (__builtin_memcmp (&i1, &i2, sizeof (i1))
|| __builtin_memcmp (&l1, &l2, sizeof (l1))
|| __builtin_memcmp (&s1, &s2, sizeof (s1))
|| __builtin_memcmp (&t1, &t2, sizeof (t1))
|| __builtin_memcmp (&u1, &u2, sizeof (u1)))
__builtin_abort ();
return 0;
}

24
gcc/testsuite/c-c++-common/torture/builtin-clear-padding-2.c Normal file
View file

@ -0,0 +1,24 @@
/* PR libstdc++/88101 */
typedef int T __attribute__((aligned (16384)));
struct S { char a; short b; long double c; T d; T e; long long f; };
__attribute__((noipa)) void
foo (struct S *s)
{
s->a = -1; s->b = -1; s->c = -18.52L; s->d = -1; s->e = -1; s->f = -1;
}
int
main ()
{
struct S s1, s2;
__builtin_memset (&s1, 0, sizeof (s1));
__builtin_memset (&s2, -1, sizeof (s2));
foo (&s1);
foo (&s2);
__builtin_clear_padding (&s2);
if (__builtin_memcmp (&s1, &s2, sizeof (s1)))
__builtin_abort ();
return 0;
}

65
gcc/testsuite/c-c++-common/torture/builtin-clear-padding-3.c Normal file
View file

@ -0,0 +1,65 @@
/* PR libstdc++/88101 */
union V { char a; signed char b; unsigned char c; };
struct T { char a; int b; union V c; };
union U { int a; long double b; struct T c; };
struct S { char a; union U b; long long c; char d; } s1, s2;
__attribute__((noipa)) void
foo (struct S *s, int x)
{
s->a = -1; s->c = -1; s->d = -1;
switch (x)
{
case 0:
s->b.a = -1;
break;
case 1:
s->b.b = -12345.25L;
break;
case 2:
s->b.c.a = -1;
s->b.c.b = -1;
s->b.c.c.b = -1;
break;
}
}
int
main ()
{
__builtin_memset (&s1, 0, sizeof (s1));
__builtin_memset (&s2, -1, sizeof (s2));
foo (&s1, 0);
foo (&s2, 0);
__builtin_clear_padding (&s2);
if (s2.b.a != (char) -1)
__builtin_abort ();
__builtin_clear_padding (&s2.b.a);
__builtin_memset (&s2.b.a + 1, 0, sizeof (union U) - sizeof (s2.b.a));
if (__builtin_memcmp (&s1, &s2, sizeof (s1)))
__builtin_abort ();
__builtin_memset (&s1, 0, sizeof (s1));
__builtin_memset (&s2, -1, sizeof (s2));
foo (&s1, 1);
foo (&s2, 1);
__builtin_clear_padding (&s2);
if (s2.b.b != -12345.25L)
__builtin_abort ();
__builtin_clear_padding (&s2.b.b);
__builtin_memset (&s2.b.b + 1, 0, sizeof (union U) - sizeof (s2.b.b));
if (__builtin_memcmp (&s1, &s2, sizeof (s1)))
__builtin_abort ();
__builtin_memset (&s1, 0, sizeof (s1));
__builtin_memset (&s2, -1, sizeof (s2));
foo (&s1, 2);
foo (&s2, 2);
__builtin_clear_padding (&s2);
if (s2.b.c.a != (char) -1 || s2.b.c.b != -1 || s2.b.c.c.b != -1)
__builtin_abort ();
__builtin_clear_padding (&s2.b.c);
__builtin_memset (&s2.b.c + 1, 0, sizeof (union U) - sizeof (s2.b.c));
if (__builtin_memcmp (&s1, &s2, sizeof (s1)))
__builtin_abort ();
return 0;
}

59
gcc/testsuite/c-c++-common/torture/builtin-clear-padding-4.c Normal file
View file

@ -0,0 +1,59 @@
/* PR libstdc++/88101 */
struct S { char a; short b; char c; };
__attribute__((noipa)) void
foo (int m, int n, int o)
{
long double a1[m];
long double a2[m];
struct S b1[m][n];
struct S b2[m][n];
struct S c1[m][n][o];
struct S c2[m][n][o];
int i, j, k;
__builtin_memset (&a1, 0, sizeof (a1));
__builtin_memset (&a2, ~0, sizeof (a2));
__builtin_memset (&b1, 0, sizeof (b1));
__builtin_memset (&b2, ~0, sizeof (b2));
__builtin_memset (&c1, 0, sizeof (c1));
__builtin_memset (&c2, ~0, sizeof (c2));
for (i = 0; i < m; i++)
{
a1[i] = 13.132L;
a2[i] = 13.132L;
for (j = 0; j < n; j++)
{
b1[i][j].a = -1;
b1[i][j].b = -1;
b1[i][j].c = -1;
b2[i][j].a = -1;
b2[i][j].b = -1;
b2[i][j].c = -1;
for (k = 0; k < o; k++)
{
c1[i][j][k].a = -1;
c1[i][j][k].b = -1;
c1[i][j][k].c = -1;
c2[i][j][k].a = -1;
c2[i][j][k].b = -1;
c2[i][j][k].c = -1;
}
}
}
__builtin_clear_padding (&a2);
__builtin_clear_padding (&b2);
__builtin_clear_padding (&c2);
if (__builtin_memcmp (&a1, &a2, sizeof (a1))
|| __builtin_memcmp (&b1, &b2, sizeof (b1))
|| __builtin_memcmp (&c1, &c2, sizeof (c1)))
__builtin_abort ();
}
int
main ()
{
foo (5, 3, 4);
foo (17, 2, 1);
return 0;
}

49
gcc/testsuite/c-c++-common/torture/builtin-clear-padding-5.c Normal file
View file

@ -0,0 +1,49 @@
/* PR libstdc++/88101 */
struct S { char a; short b; char c; } s1[24], s2[24];
struct T { char a; long long b; char c; struct S d[3]; long long e; char f; } t1, t2;
struct U { char a; long long b; char c; struct S d[25]; long long e; char f; } u1, u2;
__attribute__((noipa)) void
foo (struct S *s, struct T *t, struct U *u)
{
int i;
t->a = -1; t->b = -1; t->c = -1; t->e = -1; t->f = -1;
u->a = -1; u->b = -1; u->c = -1; u->e = -1; u->f = -1;
for (i = 0; i < 24; i++)
{
s[i].a = -1;
s[i].b = -1;
s[i].c = -1;
}
for (i = 0; i < 3; i++)
{
t->d[i].a = -1;
t->d[i].b = -1;
t->d[i].c = -1;
}
for (i = 0; i < 25; i++)
{
u->d[i].a = -1;
u->d[i].b = -1;
u->d[i].c = -1;
}
}
int
main ()
{
__builtin_memset (&s2, -1, sizeof (s2));
__builtin_memset (&t2, -1, sizeof (t2));
__builtin_memset (&u2, -1, sizeof (u2));
foo (&s1[0], &t1, &u1);
foo (&s2[0], &t2, &u2);
__builtin_clear_padding (&s2);
__builtin_clear_padding (&t2);
__builtin_clear_padding (&u2);
if (__builtin_memcmp (&s1, &s2, sizeof (s1))
|| __builtin_memcmp (&t1, &t2, sizeof (t1))
|| __builtin_memcmp (&u1, &u2, sizeof (u1)))
__builtin_abort ();
return 0;
}

31
gcc/testsuite/g++.dg/torture/builtin-clear-padding-1.C Normal file
View file

@ -0,0 +1,31 @@
/* PR libstdc++/88101 */
struct S {} s1, s2;
struct T : public S { char a; short b; char c; } t1, t2;
struct U : public T { char d; long long e; char f; } u1, u2;
__attribute__((noipa)) void
foo (T *t, U *u)
{
int i;
t->a = -1; t->b = -1; t->c = -1;
u->a = -1; u->b = -1; u->c = -1; u->d = -1; u->e = -1; u->f = -1;
}
int
main ()
{
__builtin_memset (&s2, -1, sizeof (s2));
__builtin_memset (&t2, -1, sizeof (t2));
__builtin_memset (&u2, -1, sizeof (u2));
foo (&t1, &u1);
foo (&t2, &u2);
__builtin_clear_padding (&s2);
__builtin_clear_padding (&t2);
__builtin_clear_padding (&u2);
if (__builtin_memcmp (&s1, &s2, sizeof (s1))
|| __builtin_memcmp (&t1, &t2, sizeof (t1))
|| __builtin_memcmp (&u1, &u2, sizeof (u1)))
__builtin_abort ();
return 0;
}

34
gcc/testsuite/g++.dg/torture/builtin-clear-padding-2.C Normal file
View file

@ -0,0 +1,34 @@
/* PR libstdc++/88101 */
#include <new>
struct S { char a; short b; char c; long long d; char e; decltype (nullptr) f; char g; };
alignas (S) unsigned char buf1[sizeof (S)];
alignas (S) unsigned char buf2[sizeof (S)];
template <int N>
void
foo ()
{
__builtin_clear_padding ((S *) buf2);
}
void
bar (S *s)
{
s->a = -1; s->b = -1; s->c = -1; s->d = -1; s->e = -1; s->g = -1;
}
int
main ()
{
S *s1 = new (buf1) S;
S *s2 = new (buf2) S;
__builtin_memset (s1, 0, sizeof (S));
__builtin_memset (s2, ~0, sizeof (S));
bar (s1);
bar (s2);
foo <0> ();
if (__builtin_memcmp (s1, s2, sizeof (S)) != 0)
__builtin_abort ();
}

10
gcc/testsuite/gcc.dg/builtin-clear-padding-1.c Normal file
View file

@ -0,0 +1,10 @@
/* PR libstdc++/88101 */
/* { dg-do compile } */
/* { dg-options "" } */
void
foo (int n)
{
struct S { char a; int b[n]; long long c; } s;
__builtin_clear_padding (&s); /* { dg-message "unimplemented: __builtin_clear_padding not supported for variable length aggregates" } */
}