On Tue, Mar 20, 2012 at 12:31 AM, Mike Stump <mikest...@comcast.net> wrote: > On Mar 19, 2012, at 2:44 PM, Richard Sandiford wrote: >> Mike Stump <mikest...@comcast.net> writes: >>>> If we're going to remove the assert, we need to define stuff like >>>> that. >>> >>> Orthogonal. The rest of the compiler defines what happens, it either >>> is inconsistent, in which case it is by fiat, undefined, or it is >>> consistent, in which case that consistency defines it. The compiler >>> is free to document this in a nice way, or do, what is usually done, >>> which is to assume everybody just knows what it does. Anyway, my >>> point is, this routine doesn't define the data structure, and is >>> _completely_ orthogonal to your concern. It doesn't matter if it zero >>> extends or sign extends or is inconsistent, has bugs, doesn't have >>> bugs, is documented, or isn't documented. In every single one of >>> these cases, the code in the routine I am fixing, doesn't change. >>> That is _why_ it is orthogonal. If it weren't, you'd be able to state >>> a value for which is mattered. You can't, which is why you are wrong. >>> If you think you are not wrong, please state a value for which it >>> matters how it is defined. >> >> immed_double_const and CONST_DOUBLE are currently >> only defined for 2 HOST_WIDE_INTs. > > I don't happen to share your view. The routine is defined by documentation. > The documentation might exist in a .texi file, in this case there is no texi > file for immed_double_const I don't think, next up, it is defined by the > comments before the routine. In this case, it isn't so defined. > > The current definition reads: > > /* 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 > REAL_VALUE_TYPE and use CONST_DOUBLE_FROM_REAL_VALUE. */ > > which, is is fine, and I don't _want_ to change that definition of the > routine. I can't fix it, because it isn't broken. If it were, you would be > able to state a case where the new code behaves in a manor inconsistent with > the definition, since there is none you cannot state one, and this is _why_ > you have failed to state such a case. If you disagree, please state the case. > > Now, if you review comment is, could you please update the comments in the > routine, I would just say, oh, sure: > > Index: emit-rtl.c > =================================================================== > --- emit-rtl.c (revision 184563) > +++ emit-rtl.c (working copy) > @@ -525,10 +525,9 @@ 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) > { > @@ -540,8 +539,6 @@ 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. */ > > > Sorry I missed it. Now, on to CONST_DOUBLE. It does appear in a texi file: > > > @findex const_double > @item (const_double:@var{m} @var{i0} @var{i1} @dots{}) > Represents either a floating-point constant of mode @var{m} or an > 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}. > > @findex CONST_DOUBLE_LOW > If @var{m} is @code{VOIDmode}, the bits of the value are stored in > @var{i0} and @var{i1}. @var{i0} is customarily accessed with the macro > @code{CONST_DOUBLE_LOW} and @var{i1} with @code{CONST_DOUBLE_HIGH}. > > > Here again, I don't want to change the definition. The current definition > applies and I am merely making the code conform to it. It says that > CONST_DOUBLE is used when the _value_ of the constant is too large to fit > into HOST_BITS_PER_WIDE_INT bits. > > So, if you disagree with me, you will necessarily have to quote the > definition you are using, explain what the words mean to you _and_ state a > specific case in which the code post modification doesn't not conform with > the existing definition. You have failed yet again to do that. > > >> So, as good functions do, immed_double_const asserts that it is not being >> used out of spec. > > This does not follow from the definition. 0 is a value that fits into > HOST_BITS_PER_WIDE_INT bits. It is representable in 0 bits. > HOST_BITS_PER_WIDE_INT is zero or more, and by induction, is representable by > HOST_BITS_PER_WIDE_INT bits. > >> You want to remove that restriction on immed_double_const and CONST_DOUBLE. >> That is, you want to change their spec. We should only do that if we define >> what the new semantics are. > > You're assuming a definition for CONST_DOUBLE that only exists in your mind, > instead, please refer to the actual definition in the .texi file.
Btw, I agree with Mike here (quite obvious if you followed the old e-mail thread). But as there is some disagreement here I leave approval of the patch with the comment change to someone to break that tie ;) Thanks, Richard.