The following guards the BIT_FIELD_REF expansion fallback for
MEM_REFs of entities expanded to register (or constant) further,
avoiding large out-of-bound offsets by, when the access does not
overlap the base object, expanding the offset as if it were zero.
Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.
I didn't feel lucky enough trying to simply return const0_rtx for
fully out-of-bound accesses.
OK?
Thanks,
Richard.
PR middle-end/118692
* expr.cc (expand_expr_real_1): When expanding a MEM_REF
as BIT_FIELD_REF avoid large offsets for accesses not
overlapping the base object.
* gcc.dg/pr118692.c: New testcase.
---
gcc/expr.cc | 8 ++++++++
gcc/testsuite/gcc.dg/pr118692.c | 10 ++++++++++
2 files changed, 18 insertions(+)
create mode 100644 gcc/testsuite/gcc.dg/pr118692.c
diff --git a/gcc/expr.cc b/gcc/expr.cc
index 7f3149b85ee..10467f82c0d 100644
--- a/gcc/expr.cc
+++ b/gcc/expr.cc
@@ -11806,6 +11806,14 @@ expand_expr_real_1 (tree exp, rtx target, machine_mode
tmode,
set_mem_size (temp, int_size_in_bytes (type));
return temp;
}
+ /* When the access is fully outside of the underlying object
+ expand the offset as zero. This avoids out-of-bound
+ BIT_FIELD_REFs and generates smaller code for these cases
+ with UB. */
+ type_size = tree_to_poly_uint64 (TYPE_SIZE_UNIT (type));
+ if (!ranges_maybe_overlap_p (offset, type_size, 0,
+ GET_MODE_SIZE (DECL_MODE (base))))
+ offset = 0;
exp = build3 (BIT_FIELD_REF, type, base, TYPE_SIZE (type),
bitsize_int (offset * BITS_PER_UNIT));
REF_REVERSE_STORAGE_ORDER (exp) = reverse;
diff --git a/gcc/testsuite/gcc.dg/pr118692.c b/gcc/testsuite/gcc.dg/pr118692.c
new file mode 100644
index 00000000000..49cff35b8b7
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr118692.c
@@ -0,0 +1,10 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+_Complex cf;
+
+void
+foo(char c)
+{
+ cf += *(_Complex *)__builtin_memcpy(8143523003042804629 + &c, 0, 0);
+}
--
2.43.0
