Re: C++ delayed folding branch review

[Kai Tietz <ktietz70@googlemail.com>]

2015-07-29 19:48 GMT+02:00 Jason Merrill <jason@redhat.com>:
> On 07/28/2015 04:10 PM, Kai Tietz wrote:
>>
>> 2015-07-28 1:14 GMT+02:00 Kai Tietz <ktietz70@googlemail.com>:
>>
>>> 2015-07-27 18:51 GMT+02:00 Jason Merrill <jason@redhat.com>:
>>>>
>>>> I've trimmed this to the previously mentioned issues that still need to
>>>> be
>>>> addressed; I'll do another full review after these are dealt with.
>>>
>>>
>>> Thanks for doing this summary of missing parts of prior review.
>>>
>>>> On 06/13/2015 12:15 AM, Jason Merrill wrote:
>>>>>
>>>>>
>>>>> On 06/12/2015 12:11 PM, Kai Tietz wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>> @@ -1052,6 +1054,9 @@ adjust_temp_type (tree type, tree temp)
>>>>>>>>    {
>>>>>>>>      if (TREE_TYPE (temp) == type)
>>>>>>>>        return temp;
>>>>>>>> +  STRIP_NOPS (temp);
>>>>>>>> +  if (TREE_TYPE (temp) == type)
>>>>>>>> +    return temp;
>>>>>>>> @@ -1430,6 +1438,8 @@ cxx_eval_call_expression (const constexpr_ctx
>>>>>>>> *ctx,
>>>>>>>> tree t,
>>>>>>>>    bool
>>>>>>>>    reduced_constant_expression_p (tree t)
>>>>>>>>    {
>>>>>>>> +  /* Make sure we remove useless initial NOP_EXPRs.  */
>>>>>>>> +  STRIP_NOPS (t);
>
> ^
>

Checked, and removing those STRIP_NOPS cause regressions about
vector-casts.  At least the STRIP_NOPS in
reduced_constant_expression_p seems to be required.  See as example
g++.dg/ext/vector20.C as testcase.
It sees that '(vec)(const __vector(2) long int){3l, 4l}' is not a
constant expression.

The change to adjust_temp_type seems to be no more necessary (just
doing tests on it).

>>>>>>>> @@ -1088,7 +1093,10 @@ cxx_bind_parameters_in_call (const
>>>>>>>> constexpr_ctx
>>>>>>>> *ctx, tree t,
>>>>>>>>             && is_dummy_object (x))
>>>>>>>>           {
>>>>>>>>             x = ctx->object;
>>>>>>>> -         x = cp_build_addr_expr (x, tf_warning_or_error);
>>>>>>>> +         if (x)
>>>>>>>> +           x = cp_build_addr_expr (x, tf_warning_or_error);
>>>>>>>> +         else
>>>>>>>> +           x = get_nth_callarg (t, i);
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> This still should not be necessary.

Replaced the x = get_nth_callarg (t,i);  by a gcc_unreachable ();,
just to be sure we hit issue, if occures.

>>>>>>
>>>>>>
>>>>>> Yeah, most likely.  But I got initially here some issues, so I don't
>>>>>> see that this code would worsen things.
>>>>>
>>>>>
>>>>>
>>>>> If this code path is hit, that means something has broken my design,
>>>>> and
>>>>> I don't want to just paper over that.  Please revert this change.
>
>
> ^
>
>>>>>>>>        case SIZEOF_EXPR:
>>>>>>>> +      if (processing_template_decl
>>>>>>>> +         && (!COMPLETE_TYPE_P (TREE_TYPE (t))
>>>>>>>> +         || TREE_CODE (TYPE_SIZE (TREE_TYPE (t))) != INTEGER_CST))
>>>>>>>> +       return t;
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Why is this necessary?

The issue is that by delayed-folding we don't fold sizeof-expressions
until we do the folding after genericize-pass.  So those expressions
remain, and we can run in template on sizeof-operators on incomplete
types, if we invoke here variants of the constexpr-code.  So this
pattern simply verifies that the sizeof-operand can be determined.  We
could simply avoid resolving sizeof-operators in template-decl at all.
But my idea here was to try to resolve them, if the type of the
operand is already complete (and has an constant size).

>>>>>>
>>>>>>
>>>>>> We don't want to resolve SIZEOF_EXPR within template-declarations for
>>>>>> incomplete types, of if its size isn't fixed.  Issue is that we
>>>>>> otherwise get issues about expressions without existing type (as usual
>>>>>> within template-declarations for some expressions).
>>>>>
>>>>>
>>>>>
>>>>> Yes, but we shouldn't have gotten this far with a dependent sizeof;
>>>>> maybe_constant_value just returns if
>>>>> instantiation_dependent_expression_p is true.
>
> ^

Well, but we could come here by other routine then
maybe_constant_value. For example cxx_constnat_value doesn't do checks
here.

>
>>>>>>>> @@ -3391,8 +3431,23 @@ cxx_eval_constant_expression (const
>>>>>>>> constexpr_ctx
>>>>>>>> *ctx, tree t,
>>>>>>>>        case CONVERT_EXPR:
>>>>>>>>        case VIEW_CONVERT_EXPR:
>>>>>>>>        case NOP_EXPR:
>>>>>>>> +    case UNARY_PLUS_EXPR:
>>>>>>>>          {
>>>>>>>> +       enum tree_code tcode = TREE_CODE (t);
>>>>>>>>           tree oldop = TREE_OPERAND (t, 0);
>>>>>>>> +
>>>>>>>> +       if (tcode == NOP_EXPR && TREE_TYPE (t) == TREE_TYPE (oldop)
>>>>>>>> &&
>>>>>>>> TREE_OVERFLOW_P (oldop))
>>>>>>>> +         {
>>>>>>>> +           if (!ctx->quiet)
>>>>>>>> +             permerror (input_location, "overflow in constant
>>>>>>>> expression");
>>>>>>>> +           /* If we're being permissive (and are in an enforcing
>>>>>>>> +               context), ignore the overflow.  */
>>>>>>>> +           if (!flag_permissive)
>>>>>>>> +             *overflow_p = true;
>>>>>>>> +           *non_constant_p = true;
>>>>>>>> +
>>>>>>>> +           return t;
>>>>>>>> +         }
>>>>>>>>           tree op = cxx_eval_constant_expression (ctx, oldop,
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Why doesn't the call to cxx_eval_constant_expression at the bottom
>>>>>>> here
>>>>>>> handle oldop having TREE_OVERFLOW set?
>>>>>>
>>>>>>
>>>>>>
>>>>>> I just handled the case that we see here a wrapping NOP_EXPR around an
>>>>>> overflow.  As this isn't handled by cxx_eval_constant_expression.
>>>>>
>>>>>
>>>>>
>>>>> How does it need to be handled?  A NOP_EXPR wrapped around an overflow
>>>>> is there to indicated that the expression is non-constant, and it can't
>>>>> be simplified any farther.
>>>>>
>>>>> Please give an example of what was going wrong.
>
> ^

I did some regression-testing on it.  This looks to me like something
I missed to cleanup.  Most changes within constexpr-code aren't
necessary anymore.  But looking on that, I think I papered over some
issues I had about double-reporting of non-constant expression on
overflows.

>>>>>>>> @@ -565,6 +571,23 @@ cp_gimplify_expr (tree *expr_p, gimple_seq
>>>>>>>> *pre_p,
>>>>>>>> gimple_seq *post_p)
>>>>>>>>
>>>>>>>>      switch (code)
>>>>>>>>        {
>>>>>>>> +    case SIZEOF_EXPR:
>>>>>>>> +      if (SIZEOF_EXPR_TYPE_P (*expr_p))
>>>>>>>> +       *expr_p = cxx_sizeof_or_alignof_type (TREE_TYPE
>>>>>>>> (TREE_OPERAND
>>>>>>>> (*expr_p,
>>>>>>>> +
>>>>>>>> 0)),
>>>>>>>> +                                             SIZEOF_EXPR, false);
>>>>>>>> +      else if (TYPE_P (TREE_OPERAND (*expr_p, 0)))
>>>>>>>> +       *expr_p = cxx_sizeof_or_alignof_type (TREE_OPERAND (*expr_p,
>>>>>>>> 0),
>>>>>>>> +                                             SIZEOF_EXPR, false);
>>>>>>>> +      else
>>>>>>>> +       *expr_p = cxx_sizeof_or_alignof_expr (TREE_OPERAND (*expr_p,
>>>>>>>> 0),
>>>>>>>> +                                             SIZEOF_EXPR, false);
>>>>>>>> +      if (*expr_p == error_mark_node)
>>>>>>>> +       *expr_p = size_one_node;
>>>>>>>> +
>>>>>>>> +      *expr_p = maybe_constant_value (*expr_p);
>>>>>>>> +      ret = GS_OK;
>>>>>>>> +      break;
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Why are these surviving until gimplification time?
>>>>>>
>>>>>>
>>>>>> This might be still necessary. I will retest, when bootstrap works.
>>>>>> As we now added SIZEOF_EXPR folding to cp_fold, and if we catch all
>>>>>> expressions a sizeof can occure, this shouldn't be necessary anymore.
>>>>>> AFAIR I saw here some issues about initialzation for global-variables,
>>>>>> which weren't caught.
>>>>>
>>>>>
>>>>>
>>>>> Hmm, I wonder why you would see issues with global initializers that
>>>>> aren't seen on trunk?  In any case, if the issue is with global
>>>>> initializers, they should be handled sooner, not here.
>

They don't survice in function-context, but outside they might.  On
trunk we never will see an sizeof-expression in such case as they got
folded-away much earlier.

I will try an bootstrap with disabling it.  In ME we don't produce
sizeof-expressions anymore, so we don't need to think about
re-gimplifiying some AST AFAICS.

>
>>>>>>>> @@ -1529,8 +1532,11 @@ build_expr_type_conversion (int desires, tree
>>>>>>>> expr,
>>>>>>>> bool complain)
>>>>>>>>      tree basetype = TREE_TYPE (expr);
>>>>>>>>      tree conv = NULL_TREE;
>>>>>>>>      tree winner = NULL_TREE;
>>>>>>>> +  /* Want to see if EXPR is a constant.  See below checks for
>>>>>>>> null_node.
>>>>>>>> */
>>>>>>>> +  tree expr_folded = cp_try_fold_to_constant (expr);
>>>>>>>>
>>>>>>>> -  if (expr == null_node
>>>>>>>> +  STRIP_NOPS (expr_folded);
>>>>>>>> +  if (expr_folded == null_node
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Again, we shouldn't need to fold to check for null_node, it only
>>>>>>> occurs
>>>>>>> when explicitly written.  Folding should never produce null_node
>>>>>>> unless
>>>>>>> the argument was already null_node.
>>>>>>
>>>>>>
>>>>>>
>>>>>> Well, we need to do this for diagnostic messages AFAIR.  We want to
>>>>>> see if expression folded gets a constant, so that diagnostics getting
>>>>>> displayed right.
>>>>>
>>>>>
>>>>>
>>>>> Again, null_node is special.  It indicates that the user typed
>>>>> "__null".
>>>>> That's what we're checking for here.  Folding is both unnecessary and
>>>>> undesirable.
>

So, let us remove it ...  I expect issues about casts on integers,
which are reasoned due implicit assignments, expr won't be null_node.

>
>>>>>>>> @@ -1548,7 +1554,7 @@ build_expr_type_conversion (int desires, tree
>>>>>>>> expr,
>>>>>>>> bool complain)
>>>>>>>>        switch (TREE_CODE (basetype))
>>>>>>>>          {
>>>>>>>>          case INTEGER_TYPE:
>>>>>>>> -       if ((desires & WANT_NULL) && null_ptr_cst_p (expr))
>>>>>>>> +       if ((desires & WANT_NULL) && null_ptr_cst_p (expr_folded))
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Again, we don't want to fold before calling null_ptr_cst_p, since in
>>>>>>> C++11 only a literal 0 is a null pointer constant.  For C++98 we
>>>>>>> already
>>>>>>> fold in null_ptr_cst_p.
>>>>>>
>>>>>>
>>>>>>
>>>>>> We need to avoid useless conversion, so we should reduce to simple
>>>>>> constant-value ...
>>>>>
>>>>>
>>>>>
>>>>> No.  Again, in C++11 only "0" or "0L" is a null pointer constant.   A
>>>>> more complex expression that folds to 0 is NOT a null pointer constant.
>>>>> Folding is actively harmful here.
>>>>>
>>>>> And again, in C++98 mode null_ptr_cst_p already folds, so doing it here
>>>>> is redundant.
>>>>>
>>>>> Was I unclear?
>
>
> ^

See comment above.  I will remove folding, and check.

>>>>>>>> @@ -8496,16 +8467,18 @@ compute_array_index_type (tree name, tree
>>>>>>>> size,
>>>>>>>> tsubst_flags_t complain)
>>>>>>>>          SET_TYPE_STRUCTURAL_EQUALITY (itype);
>>>>>>>>          return itype;
>>>>>>>>        }
>>>>>>>> -
>>>>>>>> +
>>>>>>>> +  /* We need to do fully folding to determine if we have VLA, or
>>>>>>>> not.  */
>>>>>>>> +  tree size_constant = cp_try_fold_to_constant (size);
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Again, we already called maybe_constant_value.
>>>>>>
>>>>>>
>>>>>>
>>>>>> Sure, but maybe_constant_value still produces nops ...
>>>>>
>>>>>
>>>>>
>>>>> If someone tries to create an array with a size that involves
>>>>> arithmetic
>>>>> overflow, that's undefined behavior and we should probably give an
>>>>> error
>>>>> rather than fold it away.
>
>
> ^

If we need to do some reduction to constant value here, as expr might
be actually a constant, which isn't folded here.  Eg something like:
struct {
  char abc[sizeof (int) * 8];
};
Due delayed folding array index isn't necessarily reduced here.  So we
need to perform at least constant value folding for diagnostics, as we
do right now.

>>>>>>>> @@ -13078,6 +13042,8 @@ build_enumerator (tree name, tree value,
>>>>>>>> tree
>>>>>>>> enumtype, tree attributes,
>>>>>>>>      if (value)
>>>>>>>>        STRIP_TYPE_NOPS (value);
>>>>>>>>
>>>>>>>> +  if (value)
>>>>>>>> +    value = cp_try_fold_to_constant (value);
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Again, this is unnecessary because we call cxx_constant_value below.
>>>>>>
>>>>>>
>>>>>> See nops, and other unary-operations we want to reduce here to real
>>>>>> constant value ...
>>>>>
>>>>>
>>>>>
>>>>> The cxx_constant_value call below will deal with them.
>>>>
>>>>
>>>>
>>>> Likewise for grokbitfield.
>>>
>>>
>>> Hmm, AFAIR we don't call cxx_constant_value in all code-paths.  But I
>>> will look into it, and come back to you on it.
>>
>>
>> I am still on it ...  first did the other points
>
>
> Looks like this hasn't changed.

Yes, for grokbitfield current version uses fold_simple for witdth.  So
just expressions based on constants getting reduced to short form.  In
grokbitfield I don't see invocation of cxx_constant_value.  So how can
we be sure that width is reduced to integer-cst?

For build_enumerator the call is indeed superflous.

>>>>>>>> @@ -6575,6 +6578,13 @@ cp_parser_postfix_open_square_expression
>>>>>>>> (cp_parser
>>>>>>>> *parser,
>>>>>>>>           index = cp_parser_expression (parser);
>>>>>>>>        }
>>>>>>>>
>>>>>>>> +  /* For offsetof and declaration of types we need
>>>>>>>> +     constant integeral values.
>>>>>>>> +     Also we meed to fold for negative constants so that diagnostic
>>>>>>>> in
>>>>>>>> +     c-family/c-common.c doesn't fail for array-bounds.  */
>>>>>>>> +  if (for_offsetof || decltype_p
>>>>>>>> +      || (TREE_CODE (index) == NEGATE_EXPR && TREE_CODE
>>>>>>>> (TREE_OPERAND
>>>>>>>> (index, 0)) == INTEGER_CST))
>>>>>>>> +    index = cp_try_fold_to_constant (index);
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Similarly, for offsetof the folding should happen closer to where it
>>>>>>> is
>>>>>>> needed.
>>>>>>>
>>>>>>> Why is it needed for decltype, which is querying the type of an
>>>>>>> expression?
>>>>>>>
>>>>>>> For NEGATE_EXPR, we had talked about always folding a NEGATE of a
>>>>>>> constant; this isn't the right place to do it.
>>>>>>
>>>>>>
>>>>>>
>>>>>> Same as above, we need in those cases (and for -1 too) the constant
>>>>>> values early anyway.  So I saw it as more logical to have done this
>>>>>> conversion as soon as possible after initialization.
>>>>>
>>>>>
>>>>>
>>>>> I don't think this is as soon as possible; we can fold the NEGATE_EXPR
>>>>> immediately when we build it, at the end of cp_build_unary_op.
>>>>>
>>>>> I still wonder why any folding is necessary for decltype.  When I ask
>>>>> why, I want to know *why*, not just have you tell me again that it's
>>>>> needed.  I don't think it is.
>>>>>
>>>>> For offsetof, I wonder if it makes sense to extend fold_offsetof_1 to
>>>>> handle whatever additional folding is needed here.  If not, then fold
>>>>> in
>>>>> finish_offsetof, before calling fold_offsetof.
>>>>
>>>>
>>>>
>>>> I see that this is now an unconditional fold_simple, but I still don't
>>>> understand why it needs to be folded here, in the parser.
>>>
>>>
>>> The point to fold the 'value' here is for cases
>>> 'processing_template_decl' isn't false. We could move it to the
>>> else-case of the 'if (! processing_template_decl)' line for being more
>>> explicit?
>>
>>
>> Well, on looking here in more detail, we might don't that that initial
>> folding here.  As for processing_template_decl fold_simple (and
>> cp_fully_fold) doesn't do much.
>
>
> Looks like the fold is still there.

Yes, but a fold_simple one just working on constant values.  It
doesn't fold expressions like 'a == a' to a constant.  I extended
comment in current version on branch.  Additionally it invokes now the
fold_simple always.  We want to reduce index, if possible, for
diagnostics in code in c-family/c-common.c for array-bounds, for types
(they need to be fully folded), and to be sure we simplify basic
operations on constant-values.

>>>>>> Anyway, if you prefer, we can do this in builder-routines, and remove
>>>>>> at places constants aren't needed directly after parsing it those
>>>>>> calls.
>>>>>
>>>>>
>>>>>
>>>>> I want to delay it to:
>>>>>
>>>>> 1) the places where we actually care about constant values, all of
>>>>> which
>>>>> already call maybe_constant_value or cxx_constant_value, so they
>>>>> shouldn't need much change; and
>>>>> 2) the places where we want a simplified expression for warnings, where
>>>>> we should call fold_simple.
>>>>
>>>>
>>>>> Folding in the parser is wrong, most of all because template
>>>>> substitution doesn't go through the parser.
>>>>
>>>>
>>>> There are still several folds in cp_parser_omp_* that should move later.
>>>
>>>
>>> In 'cp_parser_omp_var_list_no_open' we need to fold 'length' can
>>> 'low_bound' as those values getting checked some lines below (see
>>> lines 27936, 27944).
>
>
> OK, but this seems like an typical case of needing to fold for diagnostics;
> usually in those cases you use the folded value for the diagnostics and then
> keep using the unfolded expression elsewhere.

Right.

>>> In 'cp_parser_cilk_grainsize' we fold 2nd argument of
>>> 'cp_paser_cild_for' by 'fold_simple'.  Not sure if it is worth to move
>>> operand-folding into cp_parser_cilk_for itself, as we have here just
>>> two users of 'cp_parser_cilk_for'.
>>> One time we pass 'integer_zero_node' as this argument, and the other
>>> time a binary-expression, which might be constant value.
>>> But sure we can move it into 'cp_parser_cilk_grainsize'.if you prefer?
>>
>>
>> ?
>
>
> Why does the fold need to be in the parser?

Well, if we hit it during our tree-walk in cp_fold_r, then we don't
need to fold it here.  I will check, if this is really necessary.

>>>>>>>> @@ -441,7 +441,7 @@ build_aggr_init_expr (tree type, tree init)
>>>>>>>>      else if (TREE_CODE (init) == AGGR_INIT_EXPR)
>>>>>>>>        fn = AGGR_INIT_EXPR_FN (init);
>>>>>>>>      else
>>>>>>>> -    return convert (type, init);
>>>>>>>> +    return fold (convert (type, init));
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Why fold here?
>>>>>>
>>>>>>
>>>>>>
>>>>>> We had this already in prior thread.  fold (convert ()) !=
>>>>>> fold_convert () for C++.  The fold is just there to make sure we fold
>>>>>> away useless casts.
>>>>>
>>>>>
>>>>> But why here?  Can't we fold away useless casts earlier (in convert) or
>>>>> later (when we care about having a simplified expression)?
>
>
> ^
>
>>>>>>>> @@ -3664,6 +3660,10 @@ convert_arguments (tree typelist, vec<tree,
>>>>>>>> va_gc>
>>>>>>>> **values, tree fndecl,
>>>>>>>>             && (type == 0 || TREE_CODE (type) != REFERENCE_TYPE))
>>>>>>>>           val = TREE_OPERAND (val, 0);
>>>>>>>>
>>>>>>>> +      /* For BUILT_IN_NORMAL we want to fold constants.  */
>>>>>>>> +      if (fndecl && DECL_BUILT_IN (fndecl)
>>>>>>>> +         && DECL_BUILT_IN_CLASS (fndecl) == BUILT_IN_NORMAL)
>>>>>>>> +       val = fold (val);
>>>>>>>
>>>>>>>
>>>>>>> Why?
>>>>>>
>>>>>>
>>>>>> As builtin-handlers are expecting to see constant values.
>>>>
>>>>
>>>> I would think this should be maybe_constant_value then.
>>>
>>>
>>> Why?  At the end we resolve normal-builtin via 'fold_call_expr'.  Of
>>> course we can invoke here maybe_constant_value, but it would end up in
>>> the same folding of a builtin-expression. So calling here directly
>>> 'fold' just short-cuts this.
>>
>>
>> ?
>
>
> Wait.  Why are we folding here, again?  Which builtins need to have constant
> values here, before late folding?

Well, I would have assumed here first that on builitin-functions, we
need to fold arguments (at least the constant values), as
builtin-folder-routines are depending on seeing them (eg.
builtin_expect, etc).  But by looking on code, I would assume that
this method doesn't do this ...
I am confused.  So I would assume that this fold in convert_arguments
for builtin-normal functions seems not to be necessary.  We should
handle this at other places already (and better).

>>>>>>>> @@ -7249,7 +7249,7 @@ gimplify_omp_for (tree *expr_p, gimple_seq
>>>>>>>> *pre_p)
>>>>>>>>          /* Handle OMP_FOR_COND.  */
>>>>>>>>          t = TREE_VEC_ELT (OMP_FOR_COND (for_stmt), i);
>>>>>>>>          gcc_assert (COMPARISON_CLASS_P (t));
>>>>>>>> -      gcc_assert (TREE_OPERAND (t, 0) == decl);
>>>>>>>> +      gcc_assert (TREE_OPERAND (t, 0) == decl || TREE_OPERAND (t,
>>>>>>>> 1) ==
>>>>>>>> decl);
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Why didn't delayed folding canonicalize this so that the decl is in
>>>>>>> op0?
>>>>>>
>>>>>>
>>>>>> Delay folding doesn't canonicalize this.
>>>>>
>>>>>
>>>>> Why not?  Doesn't it fold all expressions?
>>>>
>>>>
>>>> ?
>>>
>>>
>>> It fold them lately.  I will recheck this code-change.  It might be no
>>> longer required due recent changes to omp-folding.  It could be that
>>> original pattern didn't applied here anymore, and therefore statement
>>> didn't been transformed into its canonical form.  Bit I assume this
>>> could be resolved.
>
>
> ?

This hunk is necessary as we don't use cannonical-form produced by
shorten_compare anymore.  Therefore special operand can occure on
right-hand side too.

>>>>> @@ -867,7 +867,7 @@ expand_subword_shift (machine_mode op1_mode, optab
>>>>> binoptab,
>>>>>           are truncated to the mode size.  */
>>>>>         carries = expand_binop (word_mode, reverse_unsigned_shift,
>>>>>                                outof_input, const1_rtx, 0, unsignedp,
>>>>> methods);
>>>>> -      if (shift_mask == BITS_PER_WORD - 1)
>>>>> +      if (shift_mask == (unsigned HOST_WIDE_INT) (BITS_PER_WORD - 1))
>>>>
>>>>
>>>>
>>>> These should still be unnecessary.

No more.

> Looks like this is still there.

Right, didn't noticed that I haven't caught them too, while cleaning
those no longer required signed/unsigned cast modifications for
bootstrap.

>>>>>>>> @@ -1947,6 +1947,8 @@ build_complex (tree type, tree real, tree
>>>>>>>> imag)
>>>>>>>>    {
>>>>>>>>      tree t = make_node (COMPLEX_CST);
>>>>>>>>
>>>>>>>> +  real = fold (real);
>>>>>>>> +  imag = fold (imag);
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> I still think this is wrong.  The arguments should be sufficiently
>>>>>>> folded.
>>>>>>
>>>>>>
>>>>>> As we don't fold unary-operators on constants, we need to fold it at
>>>>>> some place.  AFAICS is the C++ FE not calling directly build_complex.
>>>>>> So this place was the easiest way to avoid issues with things like '-'
>>>>>> '1' etc.
>>>>>
>>>>>
>>>>> Is this because of the
>>>>>>
>>>>>>
>>>>>>        value = build_complex (NULL_TREE, convert (const_type,
>>>>>>                                                   integer_zero_node),
>>>>>> value);
>>>
>>>
>>> Might be.  This should be indeed a 'fold_convert', isn't it?
>
>
> Yes.

Applied modification to it.

>>>>> in interpret_float?  I think "convert" definitely needs to do some
>>>>> folding, since it's called from middle-end code that expects that.
>>>>
>>>>
>>>> I remember talking about "convert" doing some folding (and cp_convert
>>>> not)
>>>> in our 1:1 last week.
>>>
>>>
>>> Can't remember that.  I know that we were talking about the difference
>>> of convert and fold_convert.  convert can be used on C++ specifics,
>>> but fold_convert is something shared with ME.
>
>
> convert is called from the ME, which sometimes expects folding.
>
>>> So first 'fold_convert'
>>> isn't the same as 'fold (convert ())'.
>>> I don't find places we invoke convert () in ME.  We have some calls in
>>> convert.c (see convert_to_integer, convert_to_integer_nofold, and
>>> convert_to_real), which all used in AST only AFAICS.
>
>
> I was thinking of convert.c and fold-const.c to be part of the ME, since
> they are language-independent.  But I guess other people think of the ME
> starting with gimple.
>
> And it looks like the only language-independent uses of convert are in
> c-family; I guess many of them should change to fold_convert.

Hmm, in context of this work? Or is this more a general point about future work?

>>> I remember that we were talking about adding a standard-folding to
>>> convert for operations on constant-values (as we do for
>>> convert_to_integer).  Do you mean this?
>
>
> Yes.  But it seems that isn't necessary.
>
>>>>>>>> @@ -5080,6 +5081,7 @@ output_constructor_bitfield (oc_local_state
>>>>>>>> *local,
>>>>>>>> unsigned int bit_offset)
>>>>>>>>      while (TREE_CODE (local->val) == VIEW_CONVERT_EXPR
>>>>>>>>            || TREE_CODE (local->val) == NON_LVALUE_EXPR)
>>>>>>>>        local->val = TREE_OPERAND (local->val, 0);
>>>>>>>> +  local->val = fold (local->val);
>>>>>>>
>>>>>>>
>>>>>>> Likewise.
>>>>>>
>>>>>>
>>>>>> As soon as we can be sure that values getting fully_folded, or at
>>>>>> least folded for constants, we should be able to remove this.
>>>>>
>>>>>
>>>>> Yep, they need to be folded before we get here.
>

I didn't come to remove this line for testing.  As we fold now for
initializers more early, and cp_fold supports constructors, it could
be that we don't need this anymore.  It is on my pile.

>>>>>> @@ -3311,6 +3311,9 @@ finish_case_label (location_t loc, tree
>>>>>> low_value, tree hi
>>>>>> gh_value)
>>>>>>     low_value = case_conversion (type, low_value);
>>>>>>     high_value = case_conversion (type, high_value);
>>>>>>
>>>>>> +  low_value = cp_fully_fold (low_value);
>>>>>> +  high_value = cp_fully_fold (high_value);
>>>>>
>>>>>
>>>>>
>>>>> Again, case_conversion should have already folded constants.
>

Yes, folding is here superflous.  I will remove it.

>
>>>>>> @@ -5776,6 +5776,8 @@ convert_nontype_argument (tree type, tree expr,
>>>>>> tsubst_flags_t complain)
>>>>>>   {
>>>>>>     tree expr_type;
>>>>>>
>>>>>> +  expr = cp_try_fold_to_constant (expr);
>>>>>> +
>>>>>
>>>>>
>>>>> And here, convert_nontype_argument already uses
>>>>> maybe_constant_value/cxx_constant_value for folding constants.
>

Yes, this invocation looks useless too.  I think I introduced it for
the STRING_CST check below, but AFAICS we should assume it as
unnecessary.  I will change it and do regression-testing.

>
> Jason


By recent changes we seem to hit for c++ some additional regression.
They are related to negate-shifts for c++11.  We are hitting now the
check within cxx_constant_value.  The cxx_eval_check_shift_p sees now
that left-hand operand is negative and produces two new errors for
following tests: c-c++-common Wshift-negateive-value-*.c cases.
So we will need adjust those cases, or invoke within this
eval-function instead maybe_constant_value to avoid that ?

Kai