The following addresses a long standing issue with not preserving
accesses to non-volatile objects through volatile qualified
pointers in the case that object gets expanded to a register. The
fix is to treat accesses to an object with a volatile qualified
access as forcing that object to memory. This issue got more
exposed recently so it regressed more since GCC 11.
PR middle-end/69482
* cfgexpand.cc (discover_nonconstant_array_refs_r): Volatile
qualified accesses also force objects to memory.
* gcc.target/i386/pr69482-1.c: New testcase.
* gcc.target/i386/pr69482-2.c: Likewise.
if (IS_TYPE_OR_DECL_P (t))
*walk_subtrees = 0;
+ else if (REFERENCE_CLASS_P (t) && TREE_THIS_VOLATILE (t))
+ {
+ t = get_base_address (t);
+ if (t && DECL_P (t)
+ && DECL_MODE (t) != BLKmode
+ && !TREE_ADDRESSABLE (t))
+ bitmap_set_bit (forced_stack_vars, DECL_UID (t));
+ *walk_subtrees = 0;
+ }
else if (TREE_CODE (t) == ARRAY_REF || TREE_CODE (t) == ARRAY_RANGE_REF)
{
while (((TREE_CODE (t) == ARRAY_REF || TREE_CODE (t) == ARRAY_RANGE_REF)
--- /dev/null
+/* { dg-do compile } */
+/* { dg-options "-O3" } */
+
+static inline void memset_s(void* s, int n) {
+ volatile unsigned char * p = s;
+ for(int i = 0; i < n; ++i) {
+ p[i] = 0;
+ }
+}
+
+void test() {
+ unsigned char x[4];
+ memset_s(x, sizeof x);
+}
+
+/* { dg-final { scan-assembler-times "mov" 4 } } */
--- /dev/null
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+void bar ()
+{
+ int j;
+ *(volatile int *)&j = 0;
+}
+
+/* { dg-final { scan-assembler-times "mov" 1 } } */