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middle-end/69482 - not preserving volatile accesses

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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.
This commit is contained in:
Richard Biener 2023-01-09 12:46:28 +01:00
parent fb082e3293
commit a5a8242153
3 changed files with 35 additions and 0 deletions
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9
gcc/cfgexpand.cc
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@ -6291,6 +6291,15 @@ discover_nonconstant_array_refs_r (tree * tp, int *walk_subtrees,
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)

16
gcc/testsuite/gcc.target/i386/pr69482-1.c Normal file
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@ -0,0 +1,16 @@
/* { 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 } } */

10
gcc/testsuite/gcc.target/i386/pr69482-2.c Normal file
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@ -0,0 +1,10 @@
/* { dg-do compile } */
/* { dg-options "-O2" } */
void bar ()
{
int j;
*(volatile int *)&j = 0;
}
/* { dg-final { scan-assembler-times "mov" 1 } } */