------- Comment #3 from hjl dot tools at gmail dot com 2009-01-02 22:01 -------
i386.c has
/* Output code to set at most count & (max_size - 1) bytes starting by DEST.
*/static void
expand_setmem_epilogue_via_loop (rtx destmem, rtx destptr, rtx value,
rtx count, int max_size)
{
count =
expand_simple_binop (counter_mode (count), AND, count,
GEN_INT (max_size - 1), count, 1, OPTAB_DIRECT);
expand_set_or_movmem_via_loop (destmem, NULL, destptr, NULL,
gen_lowpart (QImode, value), count, QImode,
1, max_size / 2);
}
It seems to assume that max_size is power of 2. But there may not be
the case:
#0 expand_set_or_movmem_via_loop (destmem=0x7ffff30f17e0, srcmem=0x0,
destptr=0x7ffff30f1560, srcptr=0x0, value=0x7ffff30f1500,
count=0x7ffff30f1520, mode=QImode, unroll=1, expected_size=3)
at /export/gnu/src/gcc-work/gcc/gcc/config/i386/i386.c:16484
#1 0x0000000000b6e7d1 in expand_setmem_epilogue_via_loop (
destmem=0x7ffff30f17e0, destptr=0x7ffff30f1560, value=0x7ffff30f1500,
count=0x7ffff30f1520, max_size=7)
at /export/gnu/src/gcc-work/gcc/gcc/config/i386/i386.c:16850
#2 0x0000000000b71af6 in ix86_expand_setmem (dst=0x7ffff30f17e0,
count_exp=0x7ffff30f1520, val_exp=0x7ffff30f1500,
align_exp=0x7ffff31f4470, expected_align_exp=0x7ffff31f4470,
expected_size_exp=0x7ffff31f4440)
at /export/gnu/src/gcc-work/gcc/gcc/config/i386/i386.c:18031
#3 0x0000000000ce16cc in gen_setmemsi (operand0=0x7ffff30f1440,
operand1=0x7ffff30f1340, operand2=0x7ffff30f1500, operand3=0x7ffff31f4470,
operand4=0x7ffff31f4470, operand5=0x7ffff31f4440)
at /export/gnu/src/gcc-work/gcc/gcc/config/i386/i386.md:19126
#4 0x000000000061478b in set_storage_via_setmem (object=0x7ffff30f1440,
size=0x7ffff30f1340, val=0x7ffff30f1500, align=16, expected_align=16,
expected_size=-1) at /export/gnu/src/gcc-work/gcc/gcc/expr.c:2807
The problem comes from
if (label)
{
/* When the main loop is done, COUNT_EXP might hold original count,
while we want to copy only COUNT_EXP & SIZE_NEEDED bytes.
Epilogue code will actually copy COUNT_EXP & EPILOGUE_SIZE_NEEDED
bytes. Compensate if needed. */
if (size_needed < desired_align - align)
{
tmp =
expand_simple_binop (counter_mode (count_exp), AND, count_exp,
GEN_INT (size_needed - 1), count_exp, 1,
OPTAB_DIRECT);
size_needed = desired_align - align + 1;
if (tmp != count_exp)
emit_move_insn (count_exp, tmp);
}
emit_label (label);
LABEL_NUSES (label) = 1;
}
size_needed won't be power of 2. If we add
--- ./i386.c.align 2008-12-23 09:34:11.000000000 -0800
+++ ./i386.c 2009-01-02 14:00:33.000000000 -0800
@@ -16751,6 +16751,7 @@ expand_movmem_epilogue (rtx destmem, rtx
}
if (max_size > 8)
{
+ gcc_assert (max_size == (max_size & -max_size));
count = expand_simple_binop (GET_MODE (count), AND, count, GEN_INT
(max_size - 1),
count, 1, OPTAB_DIRECT);
expand_set_or_movmem_via_loop (destmem, srcmem, destptr, srcptr, NULL,
@@ -16844,6 +16845,7 @@ static void
expand_setmem_epilogue_via_loop (rtx destmem, rtx destptr, rtx value,
rtx count, int max_size)
{
+ gcc_assert (max_size == (max_size & -max_size));
count =
expand_simple_binop (counter_mode (count), AND, count,
GEN_INT (max_size - 1), count, 1, OPTAB_DIRECT);
we will get an error.
--
hjl dot tools at gmail dot com changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jh at suse dot cz
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38708
