* [PATCH] middle-end/69482 - not preserving volatile accesses
@ 2023-01-09 12:31 Richard Biener
0 siblings, 0 replies; only message in thread
From: Richard Biener @ 2023-01-09 12:31 UTC (permalink / raw)
To: gcc-patches
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.
Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed to trunk
sofar.
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.
---
gcc/cfgexpand.cc | 9 +++++++++
gcc/testsuite/gcc.target/i386/pr69482-1.c | 16 ++++++++++++++++
gcc/testsuite/gcc.target/i386/pr69482-2.c | 10 ++++++++++
3 files changed, 35 insertions(+)
create mode 100644 gcc/testsuite/gcc.target/i386/pr69482-1.c
create mode 100644 gcc/testsuite/gcc.target/i386/pr69482-2.c
diff --git a/gcc/cfgexpand.cc b/gcc/cfgexpand.cc
index 86783a6b661..25b1558dcb9 100644
--- a/gcc/cfgexpand.cc
+++ b/gcc/cfgexpand.cc
@@ -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)
diff --git a/gcc/testsuite/gcc.target/i386/pr69482-1.c b/gcc/testsuite/gcc.target/i386/pr69482-1.c
new file mode 100644
index 00000000000..f192261b104
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr69482-1.c
@@ -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 } } */
diff --git a/gcc/testsuite/gcc.target/i386/pr69482-2.c b/gcc/testsuite/gcc.target/i386/pr69482-2.c
new file mode 100644
index 00000000000..58e89a79333
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr69482-2.c
@@ -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 } } */
--
2.35.3
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