On Tue, 28 Jul 2026, Richard Biener wrote:
> On Tue, 28 Jul 2026, Richard Biener wrote:
>
> > On Tue, 28 Jul 2026, Richard Biener wrote:
> >
> > > On Tue, 28 Jul 2026, Thomas Schwinge wrote:
> > >
> > > > Hi Richard!
> > > >
> > > > Thanks for looking into this! Regarding your review:
> > > >
> > > > On 2026-07-28T08:11:46+0200, Richard Biener <[email protected]> wrote:
> > > > > On Fri, 24 Jul 2026, Thomas Schwinge wrote:
> > > > >> GCC supports targets without 'casesi'/'tablejump' instructions. (For
> > > > >> example, '--target=amdgcn-amdhsa', '--target=nvptx-none' -- could
> > > > >> probably be implemented, but currently isn't.) For x86_64, this can
> > > > >> be
> > > > >> "faked" by modifying 'gcc/config/i386/i386.md':
> > > > >>
> > > > >> (define_expand "tablejump"
> > > > >> [(parallel [(set (pc) (match_operand 0
> > > > >> "indirect_branch_operand"))
> > > > >> (use (label_ref (match_operand 1)))])]
> > > > >> - ""
> > > > >> + "false"
> > > > >>
> > > > >> (define_insn "*tablejump_1"
> > > > >> [(set (pc) (match_operand:W 0 "indirect_branch_operand"
> > > > >> "rBw"))
> > > > >> (use (label_ref (match_operand 1)))]
> > > > >> - ""
> > > > >> + "false"
> > > > >>
> > > > >> For such GCC configurations, we've recently acquired a number of
> > > > >> GCC/Fortran regressions à la:
> > > > >>
> > > > >> during RTL pass: expand
> > > > >>
> > > > >> [...]/source-gcc/gcc/testsuite/gfortran.dg/assumed_rank_bounds_3.f90:178:38:
> > > > >> internal compiler error: in emit_case_dispatch_table, at
> > > > >> stmt.cc:1199
> > > > >> 0x1f2d35d internal_error(char const*, ...)
> > > > >> [...]/source-gcc/gcc/diagnostic-global-context.cc:787
> > > > >> 0x8d368b fancy_abort(char const*, int, char const*)
> > > > >> [...]/source-gcc/gcc/diagnostics/context.cc:1813
> > > > >> 0x773983 emit_case_dispatch_table
> > > > >> [...]/source-gcc/gcc/stmt.cc:1199
> > > > >> 0x1078752 expand_case(gswitch*)
> > > > >> [...]/source-gcc/gcc/stmt.cc:1359
> > > > >>
> > > > >> That's 'gcc/cfgexpand.cc:expand_gimple_stmt_1', 'case GIMPLE_SWITCH:'
> > > > >> calling 'gcc/stmt.cc:expand_case', which calls
> > > > >> 'gcc/stmt.cc:emit_case_dispatch_table', which does:
> > > > >>
> > > > >> [...] try "casesi". If that
> > > > >> fails, try "tablejump". A target *must* have one of them (or
> > > > >> both).
> > > > >>
> > > > >> That means, for targets providing neither 'casesi' nor 'tablejump',
> > > > >> there
> > > > >> must not be any 'GIMPLE_SWITCH'es anymore, when getting to
> > > > >> 'gcc/cfgexpand.cc:expand_gimple_stmt_1' -- and usually there aren't,
> > > > >> due
> > > > >> to 'gcc/tree-switch-conversion.cc' doing what is appropriate; in
> > > > >> particular, 'gcc/tree-switch-conversion.h':
> > > > >>
> > > > >> /* Return whether jump table expansion is allowed. */
> > > > >> bool jump_table_cluster::is_enabled (void)
> > > > >> {
> > > > >> /* If neither casesi or tablejump is available, or
> > > > >> flag_jump_tables
> > > > >> over-ruled us, we really have no choice. */
> > > > >> if (!targetm.have_casesi () && !targetm.have_tablejump ())
> > > > >> return false;
> > > > >> [...]
> > > > >>
> > > > >> ... deciding whether to lower 'GIMPLE_SWITCH'es into other control
> > > > >> flow
> > > > >> constructs supported by the target.
> > > > >>
> > > > >> Enter recent commit
> > > > >> r17-2216-g3a8d9347f30b9d66ed6a3c7e0959c08e93ecb205
> > > > >> "fortran: Create a dedicated type for ranks and array dimensions",
> > > > >> which:
> > > > >>
> > > > >> | [...] adds a type to represent ranks and array dimension, using the
> > > > >> | same base type as originally used for the rank in array descriptors
> > > > >> | (signed char), but with the stricter bounds (0 to
> > > > >> GFC_MAX_DIMENSIONS)
> > > > >> | brought to the knowledge of the middle-end. [...]
> > > > >>
> > > > >> --- a/gcc/fortran/trans-types.cc
> > > > >> +++ b/gcc/fortran/trans-types.cc
> > > > >> [...]
> > > > >> +tree gfc_array_dim_rank_type;
> > > > >> [...]
> > > > >> @@ -1226,6 +1227,12 @@ gfc_init_types (void)
> > > > >> gfc_charlen_int_kind = get_int_kind_from_node
> > > > >> (size_type_node);
> > > > >> gfc_charlen_type_node = gfc_get_int_type
> > > > >> (gfc_charlen_int_kind);
> > > > >>
> > > > >> + gfc_array_dim_rank_type
> > > > >> + = build_range_type (signed_char_type_node,
And basing this on unsigned_char_type_node might be an easier fix?
Richard.
> > > > >> + build_zero_cst
> > > > >> (signed_char_type_node),
> > > > >> + build_int_cst
> > > > >> (signed_char_type_node,
> > > > >> +
> > > > >> GFC_MAX_DIMENSIONS));
> > > > >> [...]
> > > > >> --- a/gcc/fortran/trans-types.h
> > > > >> +++ b/gcc/fortran/trans-types.h
> > > > >> [...]
> > > > >> +/* An integral type with bounds [0, GFC_MAX_DIMENSIONS]
> > > > >> suitable to hold an
> > > > >> + array rank, or an array dimension index. */
> > > > >> +extern GTY(()) tree gfc_array_dim_rank_type;
> > > > >> [...]
> > > > >>
> > > > >> ..., that is, a "subrange wrapper"; 'gcc/tree.cc':
> > > > >>
> > > > >> /* Wrapper around build_range_type_1 with SHARED set to true. */
> > > > >>
> > > > >> tree
> > > > >> build_range_type (tree type, tree lowval, tree highval)
> > > > >> {
> > > > >> return build_range_type_1 (type, lowval, highval, true);
> > > > >> }
> > > > >>
> > > > >> /* Create a range of some discrete type TYPE (an INTEGER_TYPE,
> > > > >> ENUMERAL_TYPE
> > > > >> or BOOLEAN_TYPE) with low bound LOWVAL and high bound
> > > > >> HIGHVAL. If SHARED
> > > > >> is true, reuse such a type that has already been constructed.
> > > > >> */
> > > > >>
> > > > >> static tree
> > > > >> build_range_type_1 (tree type, tree lowval, tree highval, bool
> > > > >> shared)
> > > > >> {
> > > > >> [...]
> > > > >>
> > > > >> That one has its own 'TREE_TYPE' pointing to
> > > > >> 'signed_char_type_node', and
> > > > >> itself has 'precision:8', but 'min <[...] 0> max <[...] 15>', that
> > > > >> is, a
> > > > >> restricted range compared to 'min <[...] -128> max <[...] 127>'.
> > > > >> Nothing
> > > > >> bad with that, as far as I can tell, and supposedly that enables
> > > > >> certain
> > > > >> code optimizations, due to the more restricted range.
> > > > >>
> > > > >> Now, 'gcc/tree-switch-conversion.cc':
> > > > >>
> > > > >> /* Attempt to expand CLUSTERS as a decision tree. Return true
> > > > >> when
> > > > >> expanded. */
> > > > >>
> > > > >> bool
> > > > >> switch_decision_tree::try_switch_expansion (vec<cluster *>
> > > > >> &clusters)
> > > > >> {
> > > > >> tree index_expr = gimple_switch_index (m_switch);
> > > > >> tree index_type = TREE_TYPE (index_expr);
> > > > >> basic_block bb = gimple_bb (m_switch);
> > > > >>
> > > > >> if (gimple_switch_num_labels (m_switch) == 1
> > > > >> || range_check_type (index_type) == NULL_TREE)
> > > > >> return false;
> > > > >> [...]
> > > > >>
> > > > >> ... calls 'gcc/fold-const.cc:range_check_type':
> > > > >>
> > > > >> /* Helper routine for build_range_check and match.pd. Return
> > > > >> the type to
> > > > >> perform the check or NULL if it shouldn't be optimized. */
> > > > >>
> > > > >> tree
> > > > >> range_check_type (tree etype)
> > > > >> {
> > > > >> /* First make sure that arithmetics in this type is valid,
> > > > >> then make sure
> > > > >> that it wraps around. */
> > > > >> [...]
> > > > >> if (TREE_CODE (etype) == INTEGER_TYPE && !TYPE_UNSIGNED
> > > > >> (etype))
> > > > >> {
> > > > >> tree utype, minv, maxv;
> > > > >>
> > > > >> /* Check if (unsigned) INT_MAX + 1 == (unsigned) INT_MIN
> > > > >> for the type in question, as we rely on this here. */
> > > > >> utype = unsigned_type_for (etype);
> > > > >> maxv = fold_convert (utype, TYPE_MAX_VALUE (etype));
> > > > >> maxv = range_binop (PLUS_EXPR, NULL_TREE, maxv, 1,
> > > > >> build_int_cst (TREE_TYPE (maxv), 1),
> > > > >> 1);
> > > > >> minv = fold_convert (utype, TYPE_MIN_VALUE (etype));
> > > > >>
> > > > >> if (integer_zerop (range_binop (NE_EXPR, integer_type_node,
> > > > >> minv, 1, maxv, 1)))
> > > > >> etype = utype;
> > > > >> else
> > > > >> return NULL_TREE;
> > > > >> }
> > > > >> [...]
> > > > >>
> > > > >> Here we realize that 'TYPE_MAX_VALUE (gfc_array_dim_rank_type)'
> > > > >> ('15')
> > > > >> does *not* wrap around to 'TYPE_MIN_VALUE (gfc_array_dim_rank_type)'
> > > > >> ('0') when adding '1' (contrary to '127 + 1 -> -128', for example),
> > > > >> and
> > > > >> therefore we 'return NULL_TREE;', and therefore block the
> > > > >> 'GIMPLE_SWITCH'
> > > > >> lowering.
> > > > >>
> > > > >> Per my understanding, that problem has been latent, just now exposed
> > > > >> via
> > > > >> this GCC/Fortran front end change.
> > > > >>
> > > > >> Resolve this by peeling off 'INTEGER_TYPE' subrange wrappers,
> > > > >> similar to
> > > > >> how that's already being done for 'ENUMERAL_TYPE's, 'BOOLEAN_TYPE's.
> > > > >> With that, the regressions for GCN and nvptx (as well as "faked"
> > > > >> x86_64)
> > > > >> disappear, and there's no other change in test results, including
> > > > >> x86_64-pc-linux-gnu as well as powerpc64le-unknown-linux-gnu
> > > > >> bootstrap.
> > > > >>
> > > > >> PR tree-optimization/126392
> > > > >> gcc/
> > > > >> * fold-const.cc (range_check_type): Peel off subrange wrappers.
> > > > >> ---
> > > > >> gcc/fold-const.cc | 4 ++++
> > > > >> 1 file changed, 4 insertions(+)
> > > > >>
> > > > >> diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
> > > > >> index 1764942f34a..5eb25b547fe 100644
> > > > >> --- a/gcc/fold-const.cc
> > > > >> +++ b/gcc/fold-const.cc
> > > > >> @@ -5544,6 +5544,10 @@ range_check_type (tree etype)
> > > > >> etype = TREE_TYPE (etype);
> > > > >> else if (TREE_CODE (etype) == ENUMERAL_TYPE || TREE_CODE (etype)
> > > > >> == BOOLEAN_TYPE)
> > > > >> etype = lang_hooks.types.type_for_size (TYPE_PRECISION (etype),
> > > > >> 1);
> > > > >> + else if (TREE_CODE (etype) == INTEGER_TYPE
> > > > >> + && TREE_TYPE (etype))
> > > > >> + /* Peel off subrange wrappers
> > > > >> ('gcc/tree.cc:build_range_type_1'). */
> > > > >> + etype = TREE_TYPE (etype);
> > > > >
> > > > > In principle reasonable, but I wonder whether we can rely on this
> > > > > being useful for the purpose. TREE_TYPE on INTEGER_TYPE isn't
> > > > > documented
> > > >
> > > > Quite a number of front end as well as generic GCC code calls
> > > > 'build_range_type', 'build_nonshared_range_type', so this should become
> > > > documented, I infer?
> > > >
> > > > > but IIRC it is indeed set when the INTEGER_TYPE is a
> > > > > "subtype" (but I don't think it has to).
> > > >
> > > > When you say "don't think it has to", is your worry that
> > > > 'gcc/tree.cc:build_range_type_1' might not return a type with
> > > > 'TREE_TYPE'
> > > > in the 'type_hash_canon' code path (I shall run a test with a
> > > > corresponding 'gcc_assert' added), or is it something else?
> > > >
> > > > Or, is your worry that other types may have 'TREE_TYPE' set, without
> > > > being such "subrange wrappers"? Then we should disambiguate that?
> > > >
> > > > > I'll note that using this type does not get you a wrapping type
> > > > > in the original range either, so I'm not sure what the condition
> > > > > above is testing.
> > > >
> > > > I don't understand "what the condition above is testing", please
> > > > clarify?
> > > > With: 'TREE_CODE (etype) == INTEGER_TYPE && TREE_TYPE (etype)' I intend
> > > > to match (only) such "subrange wrappers", mirroring what
> > > > 'gcc/tree.cc:build_range_type_1' is doing.
> > > >
> > > > Indeed the base type ('TREE_TYPE (etype)') need not be 'unsigned'. For
> > > > example, like in my example in the Git commit log cited above, where it
> > > > was 'signed char'. But note that we don't just return that base type,
> > > > but instead assign it to 'etype' and then continue 'range_check_type'
> > > > analysis with that one. That is, in particular the "make sure that it
> > > > wraps around" code gets executed:
> > > >
> > > > if (TREE_CODE (etype) == INTEGER_TYPE && !TYPE_UNSIGNED (etype))
> > > > {
> > > > [...]
> > > > utype = unsigned_type_for (etype);
> > > > [...]
> > > >
> > > > ..., which then either returns this 'utype', or 'NULL'.
> > > >
> > > > > So you are simply by-passing the check, fixing the ICE but either
> > > > > showing the check is pointless or simply ignoring the issue when
> > > > > it doesn't pass.
> > > >
> > > > Sorry, again I don't understand what exactly this commen applies to.
> > > >
> > > > Is this about the 'range_check_type' usage in
> > > > 'gcc/tree-switch-conversion.cc:switch_decision_tree::try_switch_expansion'?
> > > > Indeed that one uses the 'range_check_type' return value only as a
> > > > boolean flag (appropriate types exists: continue vs. doesn't exist:
> > > > 'return false;'), but per my understanding the actual 'GIMPLE_SWITCH'
> > > > transformation code then individually agian calls 'range_check_type'
> > > > where necessary.
> > > >
> > > >
> > > > But please let me know if the underlying problem should be solved in
> > > > another way. I'm certainly not an expert in 'GIMPLE_SWITCH'es, and
> > > > neither do I know all the details about GCC's type system.
> > > >
> > > > I came up with this patch by tracing down what was happening, and
> > > > noticing that 'range_check_type' already does similar fix-up for
> > > > 'ENUMERAL_TYPE's, 'BOOLEAN_TYPE's, so why not similarly also for other
> > > > "subrange" types.
> > >
> > > I wonder why range_check_type jumps through hoops here:
> > >
> > > if (TREE_CODE (etype) == INTEGER_TYPE && !TYPE_UNSIGNED (etype))
> > > {
> > > tree utype, minv, maxv;
> > >
> > > /* Check if (unsigned) INT_MAX + 1 == (unsigned) INT_MIN
> > > for the type in question, as we rely on this here. */
> > > utype = unsigned_type_for (etype);
> > > maxv = fold_convert (utype, TYPE_MAX_VALUE (etype));
> > > maxv = range_binop (PLUS_EXPR, NULL_TREE, maxv, 1,
> > > build_int_cst (TREE_TYPE (maxv), 1), 1);
> > > minv = fold_convert (utype, TYPE_MIN_VALUE (etype));
> > >
> > > if (integer_zerop (range_binop (NE_EXPR, integer_type_node,
> > > minv, 1, maxv, 1)))
> > > etype = utype;
> > > else
> > > return NULL_TREE;
> > > }
> > > ...
> > > return etype;
> > >
> > > when, for an unsigned subrange type it does not bother to verify
> > > anything and when it practically ignores subrange types from
> > > ENUMERAL or BOOLEAN types by only looking at their "base" types?
> > >
> > > Why does it not just always return unsigned_type_for (etype)?!
> > >
> > > That is, what is the wrong thing it thinks might do that this
> > > guards? And why isn't that an issue for enumeral or booleans
> > > or enumeral bitint types or for the case you are adding?
> >
> > That said, if the range type were [-2, 7] based on 'signed char'
> > then we might eventually want to convert a [-2, 2] range check
> > to an unsigned compare of (unsigned)val + 2 < 4. I'm not sure
> > how this breaks when 7 + 1 isn't -2 and why it's OK to check
> > on the TREE_TYPE of the type when the switch () and the cases
> > are based on the range type (IIRC the case values never use
> > the range type but the underlying type).
> >
> > But I for sure must be missing something.
>
> This was added by r0-59059-ge1af8299421eb7 by jakub btw.
>
> > Richard.
> >
> > > Richard.
> > >
> > > >
> > > >
> > > > Grüße
> > > > Thomas
> > > >
> > >
> > >
> >
> >
>
>
--
Richard Biener <[email protected]>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Jochen Jaser, Andrew McDonald, Abhinav Puri; (HRB 36809, AG Nuernberg)
