I'd hoped the days of zero-precision INTEGER_CSTs were behind us after Richard's patch to remove min amd max values from zero-width bitfields, but a boostrap-ubsan showed otherwise. One source is in:
null_pointer_node = build_int_cst (build_pointer_type (void_type_node), 0); if no_target, since the precision of the type comes from ptr_mode, which remains the default VOIDmode. Maybe that's a bug, but setting it to an arbitrary nonzero value would also be dangerous. The other use is in the C/C++ void_zero_node, which is specifically defined as a VOID_TYPE, zero-precision INTEGER_CST. This is used by the ubsan code in some ?: tests, as well as by other places in the frontend proper. At least the ubsan use persists until gimple. This patch therefore restores the wide-int handling for zero precision, for which the length must be 1 and the single HWI must be zero. I've tried to wrap up most of the dependencies in two new functions, wi::blocks_needed (a function version of the .cc BLOCKS_NEEDED, now also used in the header) and wi::excess_bits, so that it'll be easier to remove the handling again if zero precision ever goes away. There are some remaining, easily-greppable cases that check directly for a precision of 0 though. The combination of this and the other patches allows boostrap-ubsan to complete. There are a lot of extra testsuite failures compared to a normal bootstrap, but they don't look related to wide-int. Tested on x86_64-linux-gnu and powerpc64-linux-gnu. OK to install? Thanks, Richard Index: gcc/wide-int.cc =================================================================== --- gcc/wide-int.cc 2014-05-02 16:28:07.657847935 +0100 +++ gcc/wide-int.cc 2014-05-02 16:28:09.560842845 +0100 @@ -48,8 +48,6 @@ static const HOST_WIDE_INT zeros[WIDE_IN #define HALF_INT_MASK (((HOST_WIDE_INT) 1 << HOST_BITS_PER_HALF_WIDE_INT) - 1) #define BLOCK_OF(TARGET) ((TARGET) / HOST_BITS_PER_WIDE_INT) -#define BLOCKS_NEEDED(PREC) \ - (PREC ? (((PREC) + HOST_BITS_PER_WIDE_INT - 1) / HOST_BITS_PER_WIDE_INT) : 1) #define SIGN_MASK(X) ((HOST_WIDE_INT) (X) < 0 ? -1 : 0) /* Return the value a VAL[I] if I < LEN, otherwise, return 0 or -1 @@ -69,20 +67,20 @@ safe_uhwi (const HOST_WIDE_INT *val, uns static unsigned int canonize (HOST_WIDE_INT *val, unsigned int len, unsigned int precision) { - unsigned int blocks_needed = BLOCKS_NEEDED (precision); + unsigned int blocks_needed = wi::blocks_needed (precision); HOST_WIDE_INT top; int i; if (len > blocks_needed) len = blocks_needed; + if (wi::excess_bits (len, precision) > 0) + val[len - 1] = sext_hwi (val[len - 1], precision % HOST_BITS_PER_WIDE_INT); if (len == 1) return len; top = val[len - 1]; - if (len * HOST_BITS_PER_WIDE_INT > precision) - val[len - 1] = top = sext_hwi (top, precision % HOST_BITS_PER_WIDE_INT); - if (top != 0 && top != (HOST_WIDE_INT)-1) + if (top != 0 && top != (HOST_WIDE_INT) -1) return len; /* At this point we know that the top is either 0 or -1. Find the @@ -134,7 +132,7 @@ wi::from_buffer (const unsigned char *bu /* We have to clear all the bits ourself, as we merely or in values below. */ - unsigned int len = BLOCKS_NEEDED (precision); + unsigned int len = wi::blocks_needed (precision); HOST_WIDE_INT *val = result.write_val (); for (unsigned int i = 0; i < len; ++i) val[i] = 0; @@ -180,7 +178,7 @@ wi::to_mpz (const wide_int_ref &x, mpz_t { int len = x.get_len (); const HOST_WIDE_INT *v = x.get_val (); - int excess = len * HOST_BITS_PER_WIDE_INT - x.get_precision (); + unsigned int excess = wi::excess_bits (len, x.get_precision ()); if (wi::neg_p (x, sgn)) { @@ -306,7 +304,8 @@ wi::force_to_size (HOST_WIDE_INT *val, c unsigned int xlen, unsigned int xprecision, unsigned int precision, signop sgn) { - unsigned int blocks_needed = BLOCKS_NEEDED (precision); + unsigned int blocks_needed = wi::blocks_needed (precision); + unsigned int xblocks_needed = wi::blocks_needed (xprecision); unsigned int len = blocks_needed < xlen ? blocks_needed : xlen; for (unsigned i = 0; i < len; i++) val[i] = xval[i]; @@ -318,11 +317,11 @@ wi::force_to_size (HOST_WIDE_INT *val, c /* Expanding. */ if (sgn == UNSIGNED) { - if (small_xprecision && len == BLOCKS_NEEDED (xprecision)) + if (small_xprecision && len == xblocks_needed) val[len - 1] = zext_hwi (val[len - 1], small_xprecision); else if (val[len - 1] < 0) { - while (len < BLOCKS_NEEDED (xprecision)) + while (len < xblocks_needed) val[len++] = -1; if (small_xprecision) val[len - 1] = zext_hwi (val[len - 1], small_xprecision); @@ -332,7 +331,7 @@ wi::force_to_size (HOST_WIDE_INT *val, c } else { - if (small_xprecision && len == BLOCKS_NEEDED (xprecision)) + if (small_xprecision && len == xblocks_needed) val[len - 1] = sext_hwi (val[len - 1], small_xprecision); } } @@ -372,10 +371,8 @@ selt (const HOST_WIDE_INT *a, unsigned i static inline HOST_WIDE_INT top_bit_of (const HOST_WIDE_INT *a, unsigned int len, unsigned int prec) { - int excess = len * HOST_BITS_PER_WIDE_INT - prec; unsigned HOST_WIDE_INT val = a[len - 1]; - if (excess > 0) - val <<= excess; + val <<= wi::excess_bits (len, prec); return val >> (HOST_BITS_PER_WIDE_INT - 1); } @@ -391,28 +388,16 @@ wi::eq_p_large (const HOST_WIDE_INT *op0 const HOST_WIDE_INT *op1, unsigned int op1len, unsigned int prec) { - int l0 = op0len - 1; - unsigned int small_prec = prec & (HOST_BITS_PER_WIDE_INT - 1); - if (op0len != op1len) return false; - if (op0len == BLOCKS_NEEDED (prec) && small_prec) - { - /* It does not matter if we zext or sext here, we just have to - do both the same way. */ - if (zext_hwi (op0 [l0], small_prec) != zext_hwi (op1 [l0], small_prec)) - return false; - l0--; - } - - while (l0 >= 0) - if (op0[l0] != op1[l0]) + for (unsigned int i = 0; i < op0len - 1; i++) + if (op0[i] != op1[i]) return false; - else - l0--; - return true; + unsigned HOST_WIDE_INT top0 = op0[op0len - 1]; + unsigned HOST_WIDE_INT top1 = op1[op1len - 1]; + return ((top0 ^ top1) << wi::excess_bits (op0len, prec)) == 0; } /* Return true if OP0 < OP1 using signed comparisons. */ @@ -423,7 +408,7 @@ wi::lts_p_large (const HOST_WIDE_INT *op { HOST_WIDE_INT s0, s1; unsigned HOST_WIDE_INT u0, u1; - unsigned int blocks_needed = BLOCKS_NEEDED (precision); + unsigned int blocks_needed = wi::blocks_needed (precision); unsigned int small_prec = precision & (HOST_BITS_PER_WIDE_INT - 1); int l = MAX (op0len - 1, op1len - 1); @@ -461,7 +446,7 @@ wi::cmps_large (const HOST_WIDE_INT *op0 { HOST_WIDE_INT s0, s1; unsigned HOST_WIDE_INT u0, u1; - unsigned int blocks_needed = BLOCKS_NEEDED (precision); + unsigned int blocks_needed = wi::blocks_needed (precision); unsigned int small_prec = precision & (HOST_BITS_PER_WIDE_INT - 1); int l = MAX (op0len - 1, op1len - 1); @@ -498,7 +483,7 @@ wi::ltu_p_large (const HOST_WIDE_INT *op { unsigned HOST_WIDE_INT x0; unsigned HOST_WIDE_INT x1; - unsigned int blocks_needed = BLOCKS_NEEDED (precision); + unsigned int blocks_needed = wi::blocks_needed (precision); unsigned int small_prec = precision & (HOST_BITS_PER_WIDE_INT - 1); int l = MAX (op0len - 1, op1len - 1); @@ -525,7 +510,7 @@ wi::cmpu_large (const HOST_WIDE_INT *op0 { unsigned HOST_WIDE_INT x0; unsigned HOST_WIDE_INT x1; - unsigned int blocks_needed = BLOCKS_NEEDED (precision); + unsigned int blocks_needed = wi::blocks_needed (precision); unsigned int small_prec = precision & (HOST_BITS_PER_WIDE_INT - 1); int l = MAX (op0len - 1, op1len - 1); @@ -673,7 +658,7 @@ wide_int_storage::bswap () const { wide_int result = wide_int::create (precision); unsigned int i, s; - unsigned int len = BLOCKS_NEEDED (precision); + unsigned int len = wi::blocks_needed (precision); unsigned int xlen = get_len (); const HOST_WIDE_INT *xval = get_val (); HOST_WIDE_INT *val = result.write_val (); @@ -1149,7 +1134,7 @@ wi_unpack (unsigned HOST_HALF_WIDE_INT * unsigned int i; unsigned int j = 0; unsigned int small_prec = prec & (HOST_BITS_PER_WIDE_INT - 1); - unsigned int blocks_needed = BLOCKS_NEEDED (prec); + unsigned int blocks_needed = wi::blocks_needed (prec); HOST_WIDE_INT mask; if (sgn == SIGNED) @@ -1222,7 +1207,7 @@ wi::mul_internal (HOST_WIDE_INT *val, co unsigned HOST_WIDE_INT o0, o1, k, t; unsigned int i; unsigned int j; - unsigned int blocks_needed = BLOCKS_NEEDED (prec); + unsigned int blocks_needed = wi::blocks_needed (prec); unsigned int half_blocks_needed = blocks_needed * 2; /* The sizes here are scaled to support a 2x largest mode by 2x largest mode yielding a 4x largest mode result. This is what is @@ -1426,6 +1411,9 @@ wi::popcount (const wide_int_ref &x) unsigned int i; int count; + if (x.precision == 0) + return 0; + /* The high order block is special if it is the last block and the precision is not an even multiple of HOST_BITS_PER_WIDE_INT. We have to clear out any ones above the precision before doing @@ -1645,8 +1633,8 @@ wi::divmod_internal (HOST_WIDE_INT *quot unsigned int divisor_prec, signop sgn, bool *oflow) { - unsigned int dividend_blocks_needed = 2 * BLOCKS_NEEDED (dividend_prec); - unsigned int divisor_blocks_needed = 2 * BLOCKS_NEEDED (divisor_prec); + unsigned int dividend_blocks_needed = 2 * wi::blocks_needed (dividend_prec); + unsigned int divisor_blocks_needed = 2 * wi::blocks_needed (divisor_prec); unsigned HOST_HALF_WIDE_INT b_quotient[4 * MAX_BITSIZE_MODE_ANY_INT / HOST_BITS_PER_HALF_WIDE_INT]; unsigned HOST_HALF_WIDE_INT @@ -1671,7 +1659,7 @@ wi::divmod_internal (HOST_WIDE_INT *quot /* The smallest signed number / -1 causes overflow. The dividend_len check is for speed rather than correctness. */ if (sgn == SIGNED - && dividend_len == BLOCKS_NEEDED (dividend_prec) + && dividend_len == wi::blocks_needed (dividend_prec) && divisor == -1 && wi::only_sign_bit_p (dividend)) overflow = true; @@ -1838,7 +1826,7 @@ wi::lshift_large (HOST_WIDE_INT *val, co unsigned int small_shift = shift % HOST_BITS_PER_WIDE_INT; /* The whole-block shift fills with zeros. */ - unsigned int len = BLOCKS_NEEDED (precision); + unsigned int len = wi::blocks_needed (precision); for (unsigned int i = 0; i < skip; ++i) val[i] = 0; @@ -1876,7 +1864,7 @@ rshift_large_common (HOST_WIDE_INT *val, /* Work out how many blocks are needed to store the significant bits (excluding the upper zeros or signs). */ - unsigned int len = BLOCKS_NEEDED (xprecision - shift); + unsigned int len = wi::blocks_needed (xprecision - shift); /* It's easier to handle the simple block case specially. */ if (small_shift == 0) @@ -1949,6 +1937,9 @@ wi::arshift_large (HOST_WIDE_INT *val, c int wi::clz (const wide_int_ref &x) { + if (x.precision == 0) + return 0; + /* Calculate how many bits there above the highest represented block. */ int count = x.precision - x.len * HOST_BITS_PER_WIDE_INT; @@ -1973,6 +1964,9 @@ wi::clz (const wide_int_ref &x) int wi::clrsb (const wide_int_ref &x) { + if (x.precision == 0) + return 0; + /* Calculate how many bits there above the highest represented block. */ int count = x.precision - x.len * HOST_BITS_PER_WIDE_INT; @@ -2017,6 +2011,9 @@ wi::ctz (const wide_int_ref &x) int wi::exact_log2 (const wide_int_ref &x) { + if (x.precision == 0) + return -1; + /* Reject cases where there are implicit -1 blocks above HIGH. */ if (x.len * HOST_BITS_PER_WIDE_INT < x.precision && x.sign_mask () < 0) return -1; Index: gcc/wide-int.h =================================================================== --- gcc/wide-int.h 2014-05-02 16:28:07.657847935 +0100 +++ gcc/wide-int.h 2014-05-02 16:28:09.561842842 +0100 @@ -430,6 +430,9 @@ #define WIDE_INT_REF_FOR(T) \ /* Public functions for querying and operating on integers. */ namespace wi { + unsigned int excess_bits (unsigned int, unsigned int); + unsigned int blocks_needed (unsigned int); + template <typename T> unsigned int get_precision (const T &); @@ -740,7 +743,7 @@ inline generic_wide_int <storage>::gener inline HOST_WIDE_INT generic_wide_int <storage>::to_shwi (unsigned int precision) const { - if (precision < HOST_BITS_PER_WIDE_INT) + if (precision > 0 && precision < HOST_BITS_PER_WIDE_INT) return sext_hwi (this->get_val ()[0], precision); else return this->get_val ()[0]; @@ -764,7 +767,7 @@ generic_wide_int <storage>::to_shwi () c inline unsigned HOST_WIDE_INT generic_wide_int <storage>::to_uhwi (unsigned int precision) const { - if (precision < HOST_BITS_PER_WIDE_INT) + if (precision > 0 && precision < HOST_BITS_PER_WIDE_INT) return zext_hwi (this->get_val ()[0], precision); else return this->get_val ()[0]; @@ -797,12 +800,7 @@ generic_wide_int <storage>::sign_mask () unsigned int len = this->get_len (); unsigned HOST_WIDE_INT high = this->get_val ()[len - 1]; if (!is_sign_extended) - { - unsigned int precision = this->get_precision (); - int excess = len * HOST_BITS_PER_WIDE_INT - precision; - if (excess > 0) - high <<= excess; - } + high <<= wi::excess_bits (len, this->get_precision ()); return (HOST_WIDE_INT) (high) < 0 ? -1 : 0; } @@ -1068,7 +1066,7 @@ wide_int_storage::write_val () wide_int_storage::set_len (unsigned int l, bool is_sign_extended) { len = l; - if (!is_sign_extended && len * HOST_BITS_PER_WIDE_INT > precision) + if (!is_sign_extended && wi::excess_bits (len, precision) > 0) val[len - 1] = sext_hwi (val[len - 1], precision % HOST_BITS_PER_WIDE_INT); } @@ -1347,7 +1345,7 @@ trailing_wide_int_storage::write_val () trailing_wide_int_storage::set_len (unsigned int len, bool is_sign_extended) { *m_len = len; - if (!is_sign_extended && len * HOST_BITS_PER_WIDE_INT > m_precision) + if (!is_sign_extended && wi::excess_bits (len, m_precision) > 0) m_val[len - 1] = sext_hwi (m_val[len - 1], m_precision % HOST_BITS_PER_WIDE_INT); } @@ -1368,8 +1366,7 @@ trailing_wide_int_storage::operator = (c trailing_wide_ints <N>::set_precision (unsigned int precision) { m_precision = precision; - m_max_len = ((precision + HOST_BITS_PER_WIDE_INT - 1) - / HOST_BITS_PER_WIDE_INT); + m_max_len = wi::blocks_needed (precision); } /* Return a reference to element INDEX. */ @@ -1387,9 +1384,7 @@ trailing_wide_ints <N>::operator [] (uns inline size_t trailing_wide_ints <N>::extra_size (unsigned int precision) { - unsigned int max_len = ((precision + HOST_BITS_PER_WIDE_INT - 1) - / HOST_BITS_PER_WIDE_INT); - return (N * max_len - 1) * sizeof (HOST_WIDE_INT); + return (N * wi::blocks_needed (precision) - 1) * sizeof (HOST_WIDE_INT); } /* This macro is used in structures that end with a trailing_wide_ints field @@ -1621,6 +1616,26 @@ decompose (HOST_WIDE_INT *scratch, unsig signop, bool *); } +/* If a value of length LEN blocks has more than PRECISION bits, return + the number of excess bits, otherwise return 0. For the special case + of PRECISION being zero, the single HWI must have the value zero and + there are no excess bits. Handling zero precision this way means + that the result is always a valid shift amount. */ +inline unsigned int +wi::excess_bits (unsigned int len, unsigned int precision) +{ + unsigned int excess = len * HOST_BITS_PER_WIDE_INT - precision; + return excess < HOST_BITS_PER_WIDE_INT ? excess : 0; +} + +/* Return the number of blocks needed for precision PRECISION. */ +inline unsigned int +wi::blocks_needed (unsigned int precision) +{ + return precision == 0 ? 1 : ((precision + HOST_BITS_PER_WIDE_INT - 1) + / HOST_BITS_PER_WIDE_INT); +} + /* Return the number of bits that integer X can hold. */ template <typename T> inline unsigned int @@ -1729,9 +1744,7 @@ wi::eq_p (const T1 &x, const T2 &y) return xi.val[0] == 0; /* Otherwise flush out any excess bits first. */ unsigned HOST_WIDE_INT diff = xi.val[0] ^ yi.val[0]; - int excess = HOST_BITS_PER_WIDE_INT - precision; - if (excess > 0) - diff <<= excess; + diff <<= wi::excess_bits (1, precision); return diff == 0; } return eq_p_large (xi.val, xi.len, yi.val, yi.len, precision); @@ -2323,7 +2336,9 @@ wi::add (const T1 &x, const T2 &y, signo unsigned HOST_WIDE_INT xl = xi.ulow (); unsigned HOST_WIDE_INT yl = yi.ulow (); unsigned HOST_WIDE_INT resultl = xl + yl; - if (sgn == SIGNED) + if (precision == 0) + *overflow = false; + else if (sgn == SIGNED) *overflow = (((resultl ^ xl) & (resultl ^ yl)) >> (precision - 1)) & 1; else @@ -2396,7 +2411,9 @@ wi::sub (const T1 &x, const T2 &y, signo unsigned HOST_WIDE_INT xl = xi.ulow (); unsigned HOST_WIDE_INT yl = yi.ulow (); unsigned HOST_WIDE_INT resultl = xl - yl; - if (sgn == SIGNED) + if (precision == 0) + *overflow = false; + else if (sgn == SIGNED) *overflow = (((xl ^ yl) & (resultl ^ xl)) >> (precision - 1)) & 1; else *overflow = ((resultl << (HOST_BITS_PER_WIDE_INT - precision))