From: Richard Biener <rguenther@suse.de>
Date: Tue, 28 Jan 2025 15:20:30 +0000 (+0100)
Subject: middle-end/118684 - wrongly aligned stack local during expansion
X-Git-Tag: basepoints/gcc-16~2296
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=54bdeca3c6214485d15454df30183a56ad3e473b;p=thirdparty%2Fgcc.git

middle-end/118684 - wrongly aligned stack local during expansion

The following fixes a not properly aligned stack temporary created
during RTL expansion of a MEM_REF that we handle as a BIT_FIELD_REF
whose base was allocated to a register but which was originally
aligned to allow a larger load not trapping.  While probably UB
in C the vectorizer creates aligned accesses that might overread
a (static) allocation because it is then known not to trap.

	PR middle-end/118684
	* expr.cc (expand_expr_real_1): When expanding a reference
	based on a register and we end up needing a MEM make sure
	that's aligned as the original reference required.

	* gcc.dg/pr118684.c: New testcase.
---

diff --git a/gcc/expr.cc b/gcc/expr.cc
index a06411e1c27..95f41f69fcf 100644
--- a/gcc/expr.cc
+++ b/gcc/expr.cc
@@ -12148,7 +12148,11 @@ expand_expr_real_1 (tree exp, rtx target, machine_mode tmode,
 	   and need be, put it there.  */
 	else if (CONSTANT_P (op0) || (!MEM_P (op0) && must_force_mem))
 	  {
-	    memloc = assign_temp (TREE_TYPE (tem), 1, 1);
+	    poly_int64 size;
+	    if (!poly_int_tree_p (TYPE_SIZE_UNIT (TREE_TYPE (tem)), &size))
+	      size = max_int_size_in_bytes (TREE_TYPE (tem));
+	    memloc = assign_stack_local (TYPE_MODE (TREE_TYPE (tem)), size,
+					 get_object_alignment (tem));
 	    emit_move_insn (memloc, op0);
 	    op0 = memloc;
 	    clear_mem_expr = true;
diff --git a/gcc/testsuite/gcc.dg/pr118684.c b/gcc/testsuite/gcc.dg/pr118684.c
new file mode 100644
index 00000000000..08cc24dc061
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr118684.c
@@ -0,0 +1,12 @@
+/* { dg-do run } */
+/* { dg-options "-O2" } */
+
+typedef int v4si __attribute__((vector_size(16)));
+v4si x;
+int main ()
+{
+  int b __attribute__((aligned(16)));
+  b = 0;
+  x = *(v4si *)&b;
+  return 0;
+}