From 9ba2de71815c0ea6cc940ecb50af7cc1a84579f7 Mon Sep 17 00:00:00 2001
From: Richard Biener <rguenther@suse.de>
Date: Thu, 30 Jan 2025 11:22:37 +0100
Subject: [PATCH] middle-end/118695 - missed misalign handling in MEM_REF
expansion
When MEM_REF expansion of a non-MEM falls back to a stack temporary
we fail to handle the case where the offset adjusted reference to
the temporary is not aligned according to the requirement of the
mode. We have to go through bitfield extraction or movmisalign
in this case. Fortunately there's a helper for this.
This fixes an ICE observed on arm which has sanity checks in its
move patterns for this.
PR middle-end/118695
* expr.cc (expand_expr_real_1): When expanding a MEM_REF
to a non-MEM by committing it to a stack temporary make
sure to handle misaligned accesses correctly.
* gcc.dg/pr118695.c: New testcase.
---
gcc/expr.cc | 12 ++++++++++++
gcc/testsuite/gcc.dg/pr118695.c | 9 +++++++++
2 files changed, 21 insertions(+)
create mode 100644 gcc/testsuite/gcc.dg/pr118695.c
diff --git a/gcc/expr.cc b/gcc/expr.cc
index 10467f82c0d2..f684e26cef78 100644
--- a/gcc/expr.cc
+++ b/gcc/expr.cc
@@ -11796,6 +11796,7 @@ 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);
+ unsigned align;
if (TYPE_MODE (type) == BLKmode || maybe_lt (offset, 0))
{
temp = assign_stack_temp (DECL_MODE (base),
@@ -11804,6 +11805,17 @@ expand_expr_real_1 (tree exp, rtx target, machine_mode tmode,
temp = adjust_address (temp, TYPE_MODE (type), offset);
if (TYPE_MODE (type) == BLKmode)
set_mem_size (temp, int_size_in_bytes (type));
+ /* When the original ref was misaligned so will be the
+ access to the stack temporary. Not all targets handle
+ this correctly, some will ICE in sanity checking.
+ Handle this by doing bitfield extraction when necessary. */
+ else if ((align = get_object_alignment (exp))
+ < GET_MODE_ALIGNMENT (TYPE_MODE (type)))
+ temp
+ = expand_misaligned_mem_ref (temp, TYPE_MODE (type),
+ unsignedp, align,
+ modifier == EXPAND_STACK_PARM
+ ? NULL_RTX : target, NULL);
return temp;
}
/* When the access is fully outside of the underlying object
diff --git a/gcc/testsuite/gcc.dg/pr118695.c b/gcc/testsuite/gcc.dg/pr118695.c
new file mode 100644
index 000000000000..55e3b767a21c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr118695.c
@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-options "-O" } */
+
+void * g(int obj)
+{
+ char *t = (char*)&obj;
+ t -= 1;
+ return *(int**)t;
+}
--
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