From: Richard Biener <rguenther@suse.de>
Date: Mon, 27 Jan 2025 10:28:47 +0000 (+0100)
Subject: middle-end/118643 - ICE with out-of-bound decl access
X-Git-Tag: basepoints/gcc-16~2327
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=52366356fe7b638f66c4011b8a61fb6c22b08087;p=thirdparty%2Fgcc.git

middle-end/118643 - ICE with out-of-bound decl access

When RTL expansion of an out-of-bound access of a register falls
back to a BIT_FIELD_REF we have to ensure that's valid.  The
following avoids negative offsets by expanding through a stack
temporary.

	PR middle-end/118643
	* expr.cc (expand_expr_real_1): Avoid falling back to BIT_FIELD_REF
	expansion for negative offset.

	* gcc.dg/pr118643.c: New testcase.
---

diff --git a/gcc/expr.cc b/gcc/expr.cc
index a310b2d9131..a06411e1c27 100644
--- a/gcc/expr.cc
+++ b/gcc/expr.cc
@@ -11796,13 +11796,14 @@ expand_expr_real_1 (tree exp, rtx target, machine_mode tmode,
 		&& known_eq (GET_MODE_BITSIZE (DECL_MODE (base)), type_size))
 	      return expand_expr (build1 (VIEW_CONVERT_EXPR, type, base),
 				  target, tmode, modifier);
-	    if (TYPE_MODE (type) == BLKmode)
+	    if (TYPE_MODE (type) == BLKmode || maybe_lt (offset, 0))
 	      {
 		temp = assign_stack_temp (DECL_MODE (base),
 					  GET_MODE_SIZE (DECL_MODE (base)));
 		store_expr (base, temp, 0, false, false);
-		temp = adjust_address (temp, BLKmode, offset);
-		set_mem_size (temp, int_size_in_bytes (type));
+		temp = adjust_address (temp, TYPE_MODE (type), offset);
+		if (TYPE_MODE (type) == BLKmode)
+		  set_mem_size (temp, int_size_in_bytes (type));
 		return temp;
 	      }
 	    exp = build3 (BIT_FIELD_REF, type, base, TYPE_SIZE (type),
diff --git a/gcc/testsuite/gcc.dg/pr118643.c b/gcc/testsuite/gcc.dg/pr118643.c
new file mode 100644
index 00000000000..ff2b081ae0b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr118643.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-O" } */
+
+typedef __attribute__((__vector_size__(1))) unsigned char V;
+
+V x;
+void foo()
+{
+  V v = x;
+  x = *(V *)(&v - 1);
+}