[gcc r15-579] wrong code with points-to and volatile

[gcc r15-579] wrong code with points-to and volatile

[Richard Biener]

https://gcc.gnu.org/g:a9251ab3c91c8c559d0306838575a666ae62dff4

commit r15-579-ga9251ab3c91c8c559d0306838575a666ae62dff4
Author: Richard Biener <rguenther@suse.de>
Date:   Thu May 16 12:35:28 2024 +0200

    wrong code with points-to and volatile
    
    The following fixes points-to analysis which ignores the fact that
    volatile qualified refs can result in any pointer.
    
            * tree-ssa-structalias.cc (get_constraint_for_1): For
            volatile referenced or decls use ANYTHING.
    
            * gcc.dg/tree-ssa/alias-38.c: New testcase.

Diff:
---
 gcc/testsuite/gcc.dg/tree-ssa/alias-38.c | 14 ++++++++++++++
 gcc/tree-ssa-structalias.cc              |  7 +++++++
 2 files changed, 21 insertions(+)

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/alias-38.c b/gcc/testsuite/gcc.dg/tree-ssa/alias-38.c
new file mode 100644
index 000000000000..a5c414934735
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/alias-38.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+int x;
+int y;
+
+int main ()
+{
+  int *volatile p = &x;
+  return (p != &y);
+}
+
+/* { dg-final { scan-tree-dump " != &y" "optimized" } } */
+/* { dg-final { scan-tree-dump-not "return 1;" "optimized" } } */
diff --git a/gcc/tree-ssa-structalias.cc b/gcc/tree-ssa-structalias.cc
index bb59c6a7c023..0bac1a1f045a 100644
--- a/gcc/tree-ssa-structalias.cc
+++ b/gcc/tree-ssa-structalias.cc
@@ -3575,6 +3575,10 @@ get_constraint_for_1 (tree t, vec<ce_s> *results, bool address_p,
       }
     case tcc_reference:
       {
+	if (TREE_THIS_VOLATILE (t))
+	  /* Fall back to anything.  */
+	  break;
+
 	switch (TREE_CODE (t))
 	  {
 	  case MEM_REF:
@@ -3676,6 +3680,9 @@ get_constraint_for_1 (tree t, vec<ce_s> *results, bool address_p,
       }
     case tcc_declaration:
       {
+	if (VAR_P (t) && TREE_THIS_VOLATILE (t))
+	  /* Fall back to anything.  */
+	  break;
 	get_constraint_for_ssa_var (t, results, address_p);
 	return;
       }