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PR 69400: Invalid 128-bit modulus result

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As described in the PR, wi::divmod_internal was sign- rather than
zero-extending a modulus result in cases where the result has fewer
HWIs than the precision and the upper bit of the upper HWI was set.

This patch tries to make things more robust by getting wi_pack
to handle the canonicalisation step itself.

Tested on x86_64-linux-gnu.  I added tests to the wide-int
plugin since that seemed more direct.

gcc/
	PR tree-optimization/69400
	* wide-int.cc (wi_pack): Take the precision as argument and
	perform canonicalization here rather than in the callers.
	Use the main loop to handle all full-width HWIs.  Add a
	zero HWI if in_len isn't a full result.
	(wi::divmod_internal): Update accordingly.
	(wi::mul_internal): Likewise.  Simplify.

gcc/testsuite/
	PR tree-optimization/69400
	* gcc.dg/plugin/wide-int_plugin.c (test_wide_int_mod_trunc): New
	function.
	(plugin_init): Call it.
	* gcc.dg/torture/pr69400.c: New test.

From-SVN: r232817
This commit is contained in:
Richard Sandiford 2016-01-26 09:53:33 +00:00 committed by Richard Sandiford
parent 7ddfb31dfd
commit 5ee31e57d2
5 changed files with 90 additions and 30 deletions

10
gcc/ChangeLog

@ -1,3 +1,13 @@
2016-01-26 Richard Sandiford <richard.sandiford@arm.com>
PR tree-optimization/69400
* wide-int.cc (wi_pack): Take the precision as argument and
perform canonicalization here rather than in the callers.
Use the main loop to handle all full-width HWIs. Add a
zero HWI if in_len isn't a full result.
(wi::divmod_internal): Update accordingly.
(wi::mul_internal): Likewise. Simplify.
2016-01-25 Aditya Kumar <aditya.k7@samsung.com>
Sebastian Pop <s.pop@samsung.com>

8
gcc/testsuite/ChangeLog

@ -1,3 +1,11 @@
2016-01-26 Richard Sandiford <richard.sandiford@arm.com>
PR tree-optimization/69400
* gcc.dg/plugin/wide-int_plugin.c (test_wide_int_mod_trunc): New
function.
(plugin_init): Call it.
* gcc.dg/torture/pr69400.c: New test.
2016-01-26 Christophe Lyon <christophe.lyon@linaro.org>
* gcc.target/arm/pr68674.c: Check and use arm_fp effective target.

33
gcc/testsuite/gcc.dg/plugin/wide-int_plugin.c

@ -36,11 +36,44 @@ test_wide_int_round_sdiv (void)
abort ();
}
static void
test_wide_int_mod_trunc (void)
{
for (unsigned int i = 1; i < MAX_BITSIZE_MODE_ANY_INT; ++i)
{
if (wi::smod_trunc (wi::lshift (1, i + 1) - 3,
wi::lshift (1, i) - 1)
!= wi::lshift (1, i) - 2)
abort ();
for (unsigned int base = 32; base <= MAX_BITSIZE_MODE_ANY_INT; base *= 2)
for (int bias = -1; bias <= 1; ++bias)
{
unsigned int precision = base + bias;
if (i + 1 < precision && precision <= MAX_BITSIZE_MODE_ANY_INT)
{
wide_int one = wi::uhwi (1, precision);
wide_int a = wi::lshift (one, i + 1) - 3;
wide_int b = wi::lshift (one, i) - 1;
wide_int c = wi::lshift (one, i) - 2;
if (wi::umod_trunc (a, b) != c)
abort ();
if (wi::smod_trunc (a, b) != c)
abort ();
if (wi::smod_trunc (-a, b) != -c)
abort ();
if (wi::smod_trunc (a, -b) != c)
abort ();
}
}
}
}
int
plugin_init (struct plugin_name_args *plugin_info,
struct plugin_gcc_version *version)
{
test_double_int_round_udiv ();
test_wide_int_round_sdiv ();
test_wide_int_mod_trunc ();
return 0;
}

20
gcc/testsuite/gcc.dg/torture/pr69400.c Normal file

@ -0,0 +1,20 @@
/* { dg-do run { target int128 } } */
typedef unsigned __int128 u128;
u128 __attribute__((noinline, noclone))
foo(void)
{
u128 u = -2;
u %= 0xffffffffffffffffllu;
return u;
}
int
main()
{
u128 x = foo();
if (x != 0xfffffffffffffffellu)
__builtin_abort();
return 0;
}

49
gcc/wide-int.cc

@ -1214,30 +1214,32 @@ wi_unpack (unsigned HOST_HALF_WIDE_INT *result, const HOST_WIDE_INT *input,
result[j++] = mask;
}
/* The inverse of wi_unpack. IN_LEN is the the number of input
blocks. The number of output blocks will be half this amount. */
static void
wi_pack (unsigned HOST_WIDE_INT *result,
/* The inverse of wi_unpack. IN_LEN is the number of input
blocks and PRECISION is the precision of the result. Return the
number of blocks in the canonicalized result. */
static unsigned int
wi_pack (HOST_WIDE_INT *result,
const unsigned HOST_HALF_WIDE_INT *input,
unsigned int in_len)
unsigned int in_len, unsigned int precision)
{
unsigned int i = 0;
unsigned int j = 0;
unsigned int blocks_needed = BLOCKS_NEEDED (precision);
while (i + 2 < in_len)
while (i + 1 < in_len)
{
result[j++] = (unsigned HOST_WIDE_INT)input[i]
| ((unsigned HOST_WIDE_INT)input[i + 1]
<< HOST_BITS_PER_HALF_WIDE_INT);
result[j++] = ((unsigned HOST_WIDE_INT) input[i]
| ((unsigned HOST_WIDE_INT) input[i + 1]
<< HOST_BITS_PER_HALF_WIDE_INT));
i += 2;
}
/* Handle the case where in_len is odd. For this we zero extend. */
if (in_len & 1)
result[j++] = (unsigned HOST_WIDE_INT)input[i];
else
result[j++] = (unsigned HOST_WIDE_INT)input[i]
| ((unsigned HOST_WIDE_INT)input[i + 1] << HOST_BITS_PER_HALF_WIDE_INT);
result[j++] = (unsigned HOST_WIDE_INT) input[i];
else if (j < blocks_needed)
result[j++] = 0;
return canonize (result, j, precision);
}
/* Multiply Op1 by Op2. If HIGH is set, only the upper half of the
@ -1460,19 +1462,8 @@ wi::mul_internal (HOST_WIDE_INT *val, const HOST_WIDE_INT *op1val,
*overflow = true;
}
if (high)
{
/* compute [prec] <- ([prec] * [prec]) >> [prec] */
wi_pack ((unsigned HOST_WIDE_INT *) val,
&r[half_blocks_needed], half_blocks_needed);
return canonize (val, blocks_needed, prec);
}
else
{
/* compute [prec] <- ([prec] * [prec]) && ((1 << [prec]) - 1) */
wi_pack ((unsigned HOST_WIDE_INT *) val, r, half_blocks_needed);
return canonize (val, blocks_needed, prec);
}
int r_offset = high ? half_blocks_needed : 0;
return wi_pack (val, &r[r_offset], half_blocks_needed, prec);
}
/* Compute the population count of X. */
@ -1847,8 +1838,7 @@ wi::divmod_internal (HOST_WIDE_INT *quotient, unsigned int *remainder_len,
unsigned int quotient_len = 0;
if (quotient)
{
wi_pack ((unsigned HOST_WIDE_INT *) quotient, b_quotient, m);
quotient_len = canonize (quotient, (m + 1) / 2, dividend_prec);
quotient_len = wi_pack (quotient, b_quotient, m, dividend_prec);
/* The quotient is neg if exactly one of the divisor or dividend is
neg. */
if (dividend_neg != divisor_neg)
@ -1859,8 +1849,7 @@ wi::divmod_internal (HOST_WIDE_INT *quotient, unsigned int *remainder_len,
if (remainder)
{
wi_pack ((unsigned HOST_WIDE_INT *) remainder, b_remainder, n);
*remainder_len = canonize (remainder, (n + 1) / 2, dividend_prec);
*remainder_len = wi_pack (remainder, b_remainder, n, dividend_prec);
/* The remainder is always the same sign as the dividend. */
if (dividend_neg)
*remainder_len = wi::sub_large (remainder, zeros, 1, remainder,