[Bug middle-end/94600] Ignored volatile specifier on loop unrolling and bitfield misoptimization

["rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94600

--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
So for example

diff --git a/gcc/expr.c b/gcc/expr.c
index b97c217e86d..a980811c1e9 100644
--- a/gcc/expr.c
+++ b/gcc/expr.c
@@ -8263,7 +8263,8 @@ expand_constructor (tree exp, rtx target, enum
expand_modifier modifier,
   /* Handle calls that pass values in multiple non-contiguous
      locations.  The Irix 6 ABI has examples of this.  */
   if (target == 0 || ! safe_from_p (target, exp, 1)
-      || GET_CODE (target) == PARALLEL || modifier == EXPAND_STACK_PARM)
+      || GET_CODE (target) == PARALLEL || modifier == EXPAND_STACK_PARM
+      || (GET_CODE (target) == MEM && MEM_VOLATILE_P (target)))
     {
       if (avoid_temp_mem)
        return NULL_RTX;

avoids the constant folding and produces

foo:
        @ args = 0, pretend = 0, frame = 0
        @ frame_needed = 0, uses_anonymous_args = 0
        mov     r3, #655360
        ldr     r2, .L4
        push    {r4, lr}
        ldm     r2, {r4, lr}
        ldr     ip, [r2, #8]
        add     r0, r2, #12
        str     r4, [r3, #44]
        ldm     r0, {r0, r1, r2}
        str     lr, [r3, #48]
        str     ip, [r3, #52]
        str     r0, [r3, #56]
        str     r1, [r3, #60]
        str     r2, [r3, #64]
        pop     {r4, pc}

on arm.