[Bug middle-end/103031] New: [12 Regression] Missing static initializer folding with -frounding-math

[Bug middle-end/103031] New: [12 Regression] Missing static initializer folding with -frounding-math

[jsm28 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103031

            Bug ID: 103031
           Summary: [12 Regression] Missing static initializer folding
                    with -frounding-math
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jsm28 at gcc dot gnu.org
                CC: rguenth at gcc dot gnu.org
  Target Milestone: ---

One of the recent fixes to avoid inappropriate constant folding with
-frounding-math caused the following test to produce an error when building
with -frounding-math.  Static initializers in C are evaluated at translation
time, in the default rounding mode and with exceptions discarded;
-frounding-math should not affect this.  Indeed, fold-const.c has
START_FOLD_INIT and END_FOLD_INIT that are supposed to be used for static
initializer folding to implement this, but apparently aren't being effective in
this case.

Test case:

double x = -1ULL;

Errors:

t.c:1:12: error: initializer element is not computable at load time
    1 | double x = -1ULL;
      |            ^

Note: if the initializer is cast to double, things work fine; it's only the
case of implicit conversion that has the problem, so maybe something is handled
differently for folding an implicit conversion of a static initializer.

This breaks building glibc tests for some platforms:
https://sourceware.org/pipermail/libc-alpha/2021-October/132475.html

[Bug middle-end/103031] [12 Regression] Missing static initializer folding with -frounding-math

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103031

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=96862
           Keywords|                            |rejects-valid

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The C++ front-end was changed to support this via PR 96862.

[Bug c/103031] [12 Regression] Missing static initializer folding with -frounding-math

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103031

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2021-11-02
           Priority|P3                          |P1
             Status|UNCONFIRMED                 |NEW
   Target Milestone|---                         |12.0
     Ever confirmed|0                           |1
          Component|middle-end                  |c

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
I suppose the frontend is calling fold_convert directly rather than
fold_build1_initializer (FLOAT_EXPR, ...).

The frontend ends up building this via

#0  0x0000000000d53d87 in convert_to_real_1 (
    type=<real_type 0x7ffff6566348 double>, expr=<integer_cst 0x7ffff6544540>, 
    fold_p=true) at /home/rguenther/src/gcc3/gcc/convert.c:319
#1  0x0000000000d53f0a in convert_to_real (
    type=<real_type 0x7ffff6566348 double>, expr=<integer_cst 0x7ffff6544540>)
    at /home/rguenther/src/gcc3/gcc/convert.c:347
#2  0x0000000000b3cb90 in convert (type=<real_type 0x7ffff6566348 double>, 
    expr=<integer_cst 0x7ffff6544540>)
    at /home/rguenther/src/gcc3/gcc/c/c-convert.c:138
#3  0x0000000000b9f602 in convert_and_check (loc=242464, 
    type=<real_type 0x7ffff6566348 double>, expr=<integer_cst 0x7ffff6544540>)
    at /home/rguenther/src/gcc3/gcc/c-family/c-common.c:1767
#4  0x0000000000b1055e in convert_for_assignment (location=242464, expr_loc=0, 
    type=<real_type 0x7ffff6566348 double>, rhs=<integer_cst 0x7ffff6544540>, 
    origtype=<tree 0x0>, errtype=ic_init, null_pointer_constant=false, 
    fundecl=<tree 0x0>, function=<tree 0x0>, parmnum=0, warnopt=0)
    at /home/rguenther/src/gcc3/gcc/c/c-typeck.c:7032
#5  0x0000000000b18c6e in digest_init (init_loc=242464, 
    type=<real_type 0x7ffff6566348 double>, init=<integer_cst 0x7ffff6544540>, 
    origtype=<tree 0x0>, null_pointer_constant=false, strict_string=true, 
    require_constant=1) at /home/rguenther/src/gcc3/gcc/c/c-typeck.c:8217
#6  0x0000000000b16df8 in store_init_value (init_loc=242464, 
    decl=<var_decl 0x7ffff7ff5c60 x>, init=<integer_cst 0x7ffff6544540>, 
--Type <RET> for more, q to quit, c to continue without paging--
    origtype=<tree 0x0>) at /home/rguenther/src/gcc3/gcc/c/c-typeck.c:7762
#7  0x0000000000ace0e7 in finish_decl (decl=<var_decl 0x7ffff7ff5c60 x>, 
    init_loc=242464, init=<integer_cst 0x7ffff6544540>, origtype=<tree 0x0>, 
    asmspec_tree=<tree 0x0>) at /home/rguenther/src/gcc3/gcc/c/c-decl.c:5363

maybe convert_for_assignment needs to do something similar as
START/END_FOLD_INIT around the convert_and_check or convert_for_assignment
is not the correct thing to call here.  It's also odd that convert_to_real
says fold_p == true to convert_to_real_1 but that function doesn't actually
fold anything (maybe that's just all dead code).  I'm quite sure that
initializer_constant_valid_p isn't the one that has to accept a FLOAT_EXPR
here.

C frontend maintainers need to sort this out.

[Bug c/103031] [12 Regression] Missing static initializer folding with -frounding-math

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103031

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Joseph Myers <jsm28@gcc.gnu.org>:

https://gcc.gnu.org/g:600dcd74b8e614c996b492d97878660faf484094

commit r12-4872-g600dcd74b8e614c996b492d97878660faf484094
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Wed Nov 3 14:58:25 2021 +0000

    c: Fold implicit integer-to-floating conversions in static initializers
with -frounding-math [PR103031]

    Recent fixes to avoid inappropriate folding of some conversions to
    floating-point types with -frounding-math also prevented such folding
    in C static initializers, when folding (in the default rounding mode,
    exceptions discarded) is required for correctness.

    Folding for static initializers is handled via functions in
    fold-const.c calling START_FOLD_INIT and END_FOLD_INIT to adjust flags
    such as flag_rounding_math that should not apply in static initializer
    context, but no such function was being called for the folding of
    these implicit conversions to the type of the object being
    initialized, only for explicit conversions as part of the initializer.

    Arrange for relevant folding (a fold call in convert, in particular)
    to use this special initializer handling (via a new fold_init
    function, in particular).

    Because convert is used by language-independent code but defined in
    each front end, this isn't as simple as just adding a new default
    argument to it.  Instead, I added a new convert_init function; that
    then gets called by c-family code, and C and C++ need convert_init
    implementations (the C++ one does nothing different from convert and
    will never actually get called because the new convert_and_check
    argument will never be true from C++), but other languages don't.

    Bootstrapped with no regressions for x86_64-pc-linux-gnu.

    gcc/
            PR c/103031
            * fold-const.c (fold_init): New function.
            * fold-const.h (fold_init): New prototype.

    gcc/c-family/
            PR c/103031
            * c-common.c (convert_and_check): Add argument init_const.  Call
            convert_init if init_const.
            * c-common.h (convert_and_check): Update prototype.
            (convert_init): New prototype.

    gcc/c/
            PR c/103031
            * c-convert.c (c_convert): New function, based on convert.
            (convert): Make into wrapper of c_convert.
            (convert_init): New function.
            * c-typeck.c (enum impl_conv): Add ic_init_const.
            (convert_for_assignment): Handle ic_init_const like ic_init.  Add
            new argument to convert_and_check call.
            (digest_init): Pass ic_init_const to convert_for_assignment for
            initializers required to be constant.

    gcc/cp/
            PR c/103031
            * cvt.c (convert_init): New function.

    gcc/testsuite/
            PR c/103031
            * gcc.dg/init-rounding-math-1.c: New test.

[Bug c/103031] [12 Regression] Missing static initializer folding with -frounding-math

[jsm28 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103031

Joseph S. Myers <jsm28 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|NEW                         |RESOLVED

--- Comment #4 from Joseph S. Myers <jsm28 at gcc dot gnu.org> ---
Fixed for GCC 12.