From: Richard Biener <rguenther@suse.de>
Date: Wed, 29 Jan 2025 14:09:35 +0000 (+0100)
Subject: middle-end/118692 - ICE with out-of-bound ref expansion
X-Git-Tag: basepoints/gcc-16~2269
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6b56e645a7b481693fe6982f8f09ba2e07768bf8;p=thirdparty%2Fgcc.git

middle-end/118692 - ICE with out-of-bound ref expansion

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.

	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.
---

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..45fba560b35
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr118692.c
@@ -0,0 +1,10 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+_Complex double cf;
+
+void
+foo(char c)
+{
+  cf += *(_Complex double *)__builtin_memcpy(8143523003042804629LL + &c, 0, 0);
+}