Submitted by Mike Stump on March 22, 2012, 8:27 p.m.

Message ID | 83448720-93D1-483D-8B8C-08B672399E1B@comcast.net |
---|---|

State | New |

Headers | show |

Mike Stump <mikestump@comcast.net> writes: >> Sorry, with this bit, I meant that the current svn code is correct >> for GET_MODE_BITSIZE (op_mode) == HOST_BITS_PER_WIDE_INT * 2. >> In that case, hv < 0 can just mean that we have a uint128_t >> (or whatever) whose high bit happens to be set. (To be clear, I was using uint128_t as an example of a 2-HWI type, assuming we're using 64-bit HWIs -- which I hope we are for targets where this assert matters.) > Well, according to the spec, one cannot use CONST_DOUBLE to represent > a uint128 value with the high bit set. We can! And do now, even without your patch. Because... > The C frontend type plays this game, but they can, because they track > the type with the constant the the values of the constant are > interpreted exclusively in the context of the type. Since we don't > have the unsigned bit, we can't, so, either, they are speced to be > values on their own, or values dependent upon some external notion. > By changing the spec to say sign extending, we mean if the high bit is > set, the value is negative. ...it doesn't mean that we interpret the value as a negative _rtx_. As with all rtx calculations, things like signedness and saturation are decided by the operation rather than the "type" ("type" == rtx mode). For things like addition where signed vs. unsigned interpretation doesn't matter, we have a single rtx op like PLUS. For things like multiplication where it does matter, we have separate signed and unsigned variants. There is nothing to distinguish a uint128_t _register_ (i.e. TImode REG) that has the upper bit set from an int128_t register that happens to be negative. Instead the interpretation is decided by the operation. And the same principle applies to constants. There isn't, and doesn't need to be, a separate CONST_DOUBLE representation for: - an unsigned 2-HWI value that has the upper bit set and - a signed 2-HWI value that is negative The sign-extending thing is simply there to specify what happens when an N>2 HWI value is represented as a 2-HWI rtx. I.e. it's simply there to say what the implicit N-2 HWIs are. (That's why the definition only matters now that we're allowing N>2 by removing the assert.) In this context we're interpreting the value as unsigned because we have an UNSIGNED_FLOAT operation. So if the mode of the operand is exactly 2 HWIs in size, a negative high HWI simply indicates an unsigned value that has the high bit set. The same principle already applies to CONST_INT. We have long defined CONST_INT to be a sign-extending representation, in the sense that it is allowed to represent 2-HWI modes in which the upper HWI happens to be a sign extension of the lower HWI. That doesn't mean the 2-HWI constant itself is negative: it can just as easily be a high unsigned value. Whether it is signed, unsigned or neutral depends on the context of the rtx operation. All we're doing here is extending that principle to CONST_DOUBLE and modes wider than 2 HWIs. Sorry for the rather rambling explanation :-) I still think the version I suggested for this hunk is right though. Richard

Index: doc/rtl.texi =================================================================== --- doc/rtl.texi (revision 185706) +++ doc/rtl.texi (working copy) @@ -1510,7 +1510,9 @@ Represents either a floating-point const integer constant too large to fit into @code{HOST_BITS_PER_WIDE_INT} bits but small enough to fit within twice that number of bits (GCC does not provide a mechanism to represent even larger constants). In -the latter case, @var{m} will be @code{VOIDmode}. +the latter case, @var{m} will be @code{VOIDmode}. For integral values +the value is a signed value, meaning the top bit of +@code{CONST_DOUBLE_HIGH} is a sign bit. @findex CONST_DOUBLE_LOW If @var{m} is @code{VOIDmode}, the bits of the value are stored in Index: expmed.c =================================================================== --- expmed.c (revision 185706) +++ expmed.c (working copy) @@ -3135,8 +3135,10 @@ expand_mult (enum machine_mode mode, rtx { int shift = floor_log2 (CONST_DOUBLE_HIGH (op1)) + HOST_BITS_PER_WIDE_INT; - return expand_shift (LSHIFT_EXPR, mode, op0, - shift, target, unsignedp); + if (shift < 2 * HOST_BITS_PER_WIDE_INT - 1 + || GET_MODE_BITSIZE (mode) <= 2 * HOST_BITS_PER_WIDE_INT) + return expand_shift (LSHIFT_EXPR, mode, op0, + shift, target, unsignedp); } } Index: emit-rtl.c =================================================================== --- emit-rtl.c (revision 185706) +++ emit-rtl.c (working copy) @@ -517,7 +517,8 @@ immed_double_int_const (double_int i, en /* Return a CONST_DOUBLE or CONST_INT for a value specified as a pair of ints: I0 is the low-order word and I1 is the high-order word. - Do not use this routine for non-integer modes; convert to + The value is a signed value, with the high bit of i1 being the sign + bit. Do not use this routine for non-integer modes; convert to REAL_VALUE_TYPE and use CONST_DOUBLE_FROM_REAL_VALUE. */ rtx @@ -531,10 +532,9 @@ immed_double_const (HOST_WIDE_INT i0, HO 1) If GET_MODE_BITSIZE (mode) <= HOST_BITS_PER_WIDE_INT, then we use gen_int_mode. - 2) GET_MODE_BITSIZE (mode) == 2 * HOST_BITS_PER_WIDE_INT, but the value of - the integer fits into HOST_WIDE_INT anyway (i.e., i1 consists only - from copies of the sign bit, and sign of i0 and i1 are the same), then - we return a CONST_INT for i0. + 2) If the value of the integer fits into HOST_WIDE_INT anyway + (i.e., i1 consists only from copies of the sign bit, and sign + of i0 and i1 are the same), then we return a CONST_INT for i0. 3) Otherwise, we create a CONST_DOUBLE for i0 and i1. */ if (mode != VOIDmode) { @@ -546,8 +546,6 @@ immed_double_const (HOST_WIDE_INT i0, HO if (GET_MODE_BITSIZE (mode) <= HOST_BITS_PER_WIDE_INT) return gen_int_mode (i0, mode); - - gcc_assert (GET_MODE_BITSIZE (mode) == 2 * HOST_BITS_PER_WIDE_INT); } /* If this integer fits in one word, return a CONST_INT. */ Index: simplify-rtx.c =================================================================== --- simplify-rtx.c (revision 185706) +++ simplify-rtx.c (working copy) @@ -97,6 +97,7 @@ mode_signbit_p (enum machine_mode mode, width -= HOST_BITS_PER_WIDE_INT; } else + /* FIXME: We don't yet have a representation for wider modes. */ return false; if (width < HOST_BITS_PER_WIDE_INT) @@ -1355,16 +1356,10 @@ simplify_const_unary_operation (enum rtx else lv = CONST_DOUBLE_LOW (op), hv = CONST_DOUBLE_HIGH (op); - if (op_mode == VOIDmode) - { - /* We don't know how to interpret negative-looking numbers in - this case, so don't try to fold those. */ - if (hv < 0) - return 0; - } - else if (GET_MODE_PRECISION (op_mode) >= HOST_BITS_PER_WIDE_INT * 2) - ; - else + /* We should never get a negative number. */ + gcc_assert (hv >= 0); + + if (GET_MODE_PRECISION (op_mode) <= HOST_BITS_PER_WIDE_INT) hv = 0, lv &= GET_MODE_MASK (op_mode); REAL_VALUE_FROM_UNSIGNED_INT (d, lv, hv, mode); @@ -1718,7 +1713,7 @@ simplify_const_unary_operation (enum rtx else if (GET_CODE (op) == CONST_DOUBLE && SCALAR_FLOAT_MODE_P (GET_MODE (op)) && GET_MODE_CLASS (mode) == MODE_INT - && width <= 2*HOST_BITS_PER_WIDE_INT && width > 0) + && width <= 2 * HOST_BITS_PER_WIDE_INT && width > 0) { /* Although the overflow semantics of RTL's FIX and UNSIGNED_FIX operators are intentionally left unspecified (to ease implementation @@ -1783,7 +1778,7 @@ simplify_const_unary_operation (enum rtx return const0_rtx; /* Test against the unsigned upper bound. */ - if (width == 2*HOST_BITS_PER_WIDE_INT) + if (width == 2 * HOST_BITS_PER_WIDE_INT) { th = -1; tl = -1; @@ -2380,7 +2375,9 @@ simplify_binary_operation_1 (enum rtx_co || GET_MODE_CLASS (GET_MODE (trueop1)) == MODE_INT) && GET_MODE (op0) == mode && CONST_DOUBLE_LOW (trueop1) == 0 - && (val = exact_log2 (CONST_DOUBLE_HIGH (trueop1))) >= 0) + && (val = exact_log2 (CONST_DOUBLE_HIGH (trueop1))) >= 0 + && (val < 2 * HOST_BITS_PER_WIDE_INT - 1 + || GET_MODE_BITSIZE (mode) <= 2 * HOST_BITS_PER_WIDE_INT)) return simplify_gen_binary (ASHIFT, mode, op0, GEN_INT (val + HOST_BITS_PER_WIDE_INT)); @@ -5189,6 +5186,7 @@ simplify_immed_subreg (enum machine_mode case CONST_DOUBLE: if (GET_MODE (el) == VOIDmode) { + unsigned char extend = 0; /* If this triggers, someone should have generated a CONST_INT instead. */ gcc_assert (elem_bitsize > HOST_BITS_PER_WIDE_INT); @@ -5201,10 +5199,11 @@ simplify_immed_subreg (enum machine_mode = CONST_DOUBLE_HIGH (el) >> (i - HOST_BITS_PER_WIDE_INT); i += value_bit; } - /* It shouldn't matter what's done here, so fill it with - zero. */ + + if (CONST_DOUBLE_HIGH (el) >> (HOST_BITS_PER_WIDE_INT - 1)) + extend = -1; for (; i < elem_bitsize; i += value_bit) - *vp++ = 0; + *vp++ = extend; } else { Index: explow.c =================================================================== --- explow.c (revision 185706) +++ explow.c (working copy) @@ -74,14 +74,20 @@ trunc_int_for_mode (HOST_WIDE_INT c, enu return c; } -/* Return an rtx for the sum of X and the integer C. */ +/* Return an rtx for the sum of X and the integer C, given that X has + mode MODE. This routine should be used instead of plus_constant + when they want to ensure that addition happens in a particular + mode, which is necessary when x can be a VOIDmode CONST_INT or + CONST_DOUBLE and the width of the constant is different from the + width of the expression. */ +/* TODO: All callers of plus_constant should migrate to this routine, + and once they do, we can assert that mode is not VOIDmode. */ rtx -plus_constant (rtx x, HOST_WIDE_INT c) +plus_constant_mode (enum machine_mode mode, rtx x, HOST_WIDE_INT c) { RTX_CODE code; rtx y; - enum machine_mode mode; rtx tem; int all_constant = 0; @@ -91,12 +97,26 @@ plus_constant (rtx x, HOST_WIDE_INT c) restart: code = GET_CODE (x); - mode = GET_MODE (x); y = x; switch (code) { case CONST_INT: + if (GET_MODE_BITSIZE (mode) > HOST_BITS_PER_WIDE_INT) + { + unsigned HOST_WIDE_INT l1 = INTVAL (x); + HOST_WIDE_INT h1 = (l1 >> (HOST_BITS_PER_WIDE_INT - 1)) ? -1 : 0; + unsigned HOST_WIDE_INT l2 = c; + HOST_WIDE_INT h2 = c < 0 ? -1 : 0; + unsigned HOST_WIDE_INT lv; + HOST_WIDE_INT hv; + + if (add_double_with_sign (l1, h1, l2, h2, &lv, &hv, false)) + gcc_unreachable (); + + return immed_double_const (lv, hv, VOIDmode); + } + return GEN_INT (INTVAL (x) + c); case CONST_DOUBLE: @@ -104,11 +124,14 @@ plus_constant (rtx x, HOST_WIDE_INT c) unsigned HOST_WIDE_INT l1 = CONST_DOUBLE_LOW (x); HOST_WIDE_INT h1 = CONST_DOUBLE_HIGH (x); unsigned HOST_WIDE_INT l2 = c; - HOST_WIDE_INT h2 = c < 0 ? ~0 : 0; + HOST_WIDE_INT h2 = c < 0 ? -1 : 0; unsigned HOST_WIDE_INT lv; HOST_WIDE_INT hv; - add_double (l1, h1, l2, h2, &lv, &hv); + if (add_double_with_sign (l1, h1, l2, h2, &lv, &hv, false)) + /* Sorry, we have no way to represent overflows this wide. + To fix, add constant support wider than CONST_DOUBLE. */ + gcc_assert (GET_MODE_BITSIZE (mode) <= 2 * HOST_BITS_PER_WIDE_INT); return immed_double_const (lv, hv, VOIDmode); } @@ -120,10 +143,8 @@ plus_constant (rtx x, HOST_WIDE_INT c) if (GET_CODE (XEXP (x, 0)) == SYMBOL_REF && CONSTANT_POOL_ADDRESS_P (XEXP (x, 0))) { - tem - = force_const_mem (GET_MODE (x), - plus_constant (get_pool_constant (XEXP (x, 0)), - c)); + tem = plus_constant_mode (mode, get_pool_constant (XEXP (x, 0)), c); + tem = force_const_mem (GET_MODE (x), tem); if (memory_address_p (GET_MODE (tem), XEXP (tem, 0))) return tem; } @@ -142,31 +163,17 @@ plus_constant (rtx x, HOST_WIDE_INT c) break; case PLUS: - /* The interesting case is adding the integer to a sum. - Look for constant term in the sum and combine - with C. For an integer constant term, we make a combined - integer. For a constant term that is not an explicit integer, - we cannot really combine, but group them together anyway. - - Restart or use a recursive call in case the remaining operand is - something that we handle specially, such as a SYMBOL_REF. + /* The interesting case is adding the integer to a sum. Look + for constant term in the sum and combine with C. For an + integer constant term or a constant term that is not an + explicit integer, we combine or group them together anyway. We may not immediately return from the recursive call here, lest all_constant gets lost. */ - if (CONST_INT_P (XEXP (x, 1))) + if (CONSTANT_P (XEXP (x, 1))) { - c += INTVAL (XEXP (x, 1)); - - if (GET_MODE (x) != VOIDmode) - c = trunc_int_for_mode (c, GET_MODE (x)); - - x = XEXP (x, 0); - goto restart; - } - else if (CONSTANT_P (XEXP (x, 1))) - { - x = gen_rtx_PLUS (mode, XEXP (x, 0), plus_constant (XEXP (x, 1), c)); + x = gen_rtx_PLUS (mode, XEXP (x, 0), plus_constant_mode (mode, XEXP (x, 1), c)); c = 0; } else if (find_constant_term_loc (&y)) @@ -176,7 +183,7 @@ plus_constant (rtx x, HOST_WIDE_INT c) rtx copy = copy_rtx (x); rtx *const_loc = find_constant_term_loc (©); - *const_loc = plus_constant (*const_loc, c); + *const_loc = plus_constant_mode (mode, *const_loc, c); x = copy; c = 0; } @@ -196,6 +203,14 @@ plus_constant (rtx x, HOST_WIDE_INT c) else return x; } + +/* Return an rtx for the sum of X and the integer C. */ + +rtx +plus_constant (rtx x, HOST_WIDE_INT c) +{ + return plus_constant_mode (GET_MODE (x), x, c); +} /* If X is a sum, return a new sum like X but lacking any constant terms. Add all the removed constant terms into *CONSTPTR. Index: rtl.h =================================================================== --- rtl.h (revision 185706) +++ rtl.h (working copy) @@ -1644,6 +1644,7 @@ extern int ceil_log2 (unsigned HOST_WIDE /* In explow.c */ extern HOST_WIDE_INT trunc_int_for_mode (HOST_WIDE_INT, enum machine_mode); extern rtx plus_constant (rtx, HOST_WIDE_INT); +extern rtx plus_constant_mode (enum machine_mode, rtx, HOST_WIDE_INT); /* In rtl.c */ extern rtx rtx_alloc_stat (RTX_CODE MEM_STAT_DECL);