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authorJoseph Myers <josmyers@redhat.com>2025-09-20 00:24:26 +0000
committerJoseph Myers <josmyers@redhat.com>2025-09-20 00:24:26 +0000
commit3eca9b5119f235666a2d97cb77a6cddc567bbe8b (patch)
tree1de98b944bf7a5802f9efb96c4cc73330aab441e /gcc/c
parentdcc231417fcb24f90ad2563c47edee04326426a1 (diff)
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c: Implement C2y N3481 constraint against lvalue conversion with incomplete type
C2y replaces undefined behavior for lvalue conversion of an lvalue with incomplete, non-array type with a constraint violation. Implement this in GCC, which means disallowing lvalue conversion of qualified or atomic void for C2y. (Unqualified, non-atomic void is excluded from the definition of "lvalue".) I'm not convinced that the resolution of C90 DR#106 (which said that certain cases with qualified void were valid) was really justified even based on the wording of C90; nevertheless, this patch takes the conservative approach of only disallowing qualified void here for C2y. The test for this change showed that attempting to access an _Atomic void object produced an ICE-after-error attempting the atomic load logic for such a type. require_complete_type returning error_mark_node prevents this ICE from occurring any more in C2y mode; to avoid it in older modes, a check of COMPLETE_TYPE_P is added to really_atomic_lvalue. I didn't find any existing bug report in Bugzilla for this issue. Bootstrapped with no regressions for x86_64-pc-linux-gnu. gcc/c/ * c-typeck.cc (really_atomic_lvalue): Return false for incomplete types. (convert_lvalue_to_rvalue): Call require_complete_type for qualified void for C2y. gcc/testsuite/ * gcc.dg/c11-atomic-6.c, gcc.dg/c23-incomplete-1.c, gcc.dg/c2y-incomplete-3.c: New tests.
Diffstat (limited to 'gcc/c')
-rw-r--r--gcc/c/c-typeck.cc6
1 files changed, 5 insertions, 1 deletions
diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc
index 1f04a4d..624e7a3 100644
--- a/gcc/c/c-typeck.cc
+++ b/gcc/c/c-typeck.cc
@@ -2512,6 +2512,8 @@ really_atomic_lvalue (tree expr)
return false;
if (!TYPE_ATOMIC (TREE_TYPE (expr)))
return false;
+ if (!COMPLETE_TYPE_P (TREE_TYPE (expr)))
+ return false;
if (!lvalue_p (expr))
return false;
@@ -2607,7 +2609,9 @@ convert_lvalue_to_rvalue (location_t loc, struct c_expr exp,
if (convert_p)
exp = default_function_array_conversion (loc, exp);
- if (!VOID_TYPE_P (TREE_TYPE (exp.value)))
+ if (!VOID_TYPE_P (TREE_TYPE (exp.value))
+ || (flag_isoc2y
+ && TYPE_QUALS (TREE_TYPE (exp.value)) != TYPE_UNQUALIFIED))
exp.value = require_complete_type (loc, exp.value);
if (for_init || !RECORD_OR_UNION_TYPE_P (TREE_TYPE (exp.value)))
{