tree-optimization/106131 - wrong code with FRE rewriting

The following makes sure to not use the original TBAA type for
looking up a value across an aggregate copy when we had to offset
the read.

2022-06-30  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/106131
	* tree-ssa-sccvn.cc (vn_reference_lookup_3): Force alias-set
	zero when offsetting the read looking through an aggregate
	copy.

	* g++.dg/torture/pr106131.C: New testcase.

(cherry picked from commit 9701432ff79926a5dd3303be3417e0bd0c24140b)

diff --git a/gcc/testsuite/g++.dg/torture/pr106131.C b/gcc/testsuite/g++.dg/torture/pr106131.C
new file mode 100644 (file)
index 0000000..e110f4a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/torture/pr106131.C
@@ -0,0 +1,34 @@
+// { dg-do run { target c++11 } }
+
+struct Pair {
+    int a, b;
+    Pair(const Pair &) = default;
+    Pair(int _a, int _b) : a(_a), b(_b) {}
+    Pair &operator=(const Pair &z) {
+       a = z.a;
+       b = z.b;
+       return *this;
+    }
+};
+
+const int &max(const int &a, const int &b)
+{
+  return a < b ? b : a;
+}
+
+int foo(Pair x, Pair y)
+{
+  return max(x.b, y.b);
+}
+
+int main()
+{
+  auto f = new Pair[3] {{0, -11}, {0, -8}, {0, 2}};
+  for (int i = 0; i < 1; i++) {
+      f[i] = f[0];
+      if(i == 0)
+       f[i] = f[2];
+      if (foo(f[i], f[1]) != 2)
+       __builtin_abort();
+  }
+}

diff --git a/gcc/tree-ssa-sccvn.cc b/gcc/tree-ssa-sccvn.cc
index cd57379..e22c702 100644 (file)
--- a/gcc/tree-ssa-sccvn.cc
+++ b/gcc/tree-ssa-sccvn.cc
@@ -3243,12 +3243,12 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_,
       poly_int64 extra_off = 0;
       if (j == 0 && i >= 0
          && lhs_ops[0].opcode == MEM_REF
-         && maybe_ne (lhs_ops[0].off, -1))
+         && known_ne (lhs_ops[0].off, -1))
        {
          if (known_eq (lhs_ops[0].off, vr->operands[i].off))
            i--, j--;
          else if (vr->operands[i].opcode == MEM_REF
-                  && maybe_ne (vr->operands[i].off, -1))
+                  && known_ne (vr->operands[i].off, -1))
            {
              extra_off = vr->operands[i].off - lhs_ops[0].off;
              i--, j--;
@@ -3275,6 +3275,7 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_,
       copy_reference_ops_from_ref (rhs1, &rhs);
 
       /* Apply an extra offset to the inner MEM_REF of the RHS.  */
+      bool force_no_tbaa = false;
       if (maybe_ne (extra_off, 0))
        {
          if (rhs.length () < 2)
@@ -3287,6 +3288,10 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_,
          rhs[ix].op0 = int_const_binop (PLUS_EXPR, rhs[ix].op0,
                                         build_int_cst (TREE_TYPE (rhs[ix].op0),
                                                        extra_off));
+         /* When we have offsetted the RHS, reading only parts of it,
+            we can no longer use the original TBAA type, force alias-set
+            zero.  */
+         force_no_tbaa = true;
        }
 
       /* Save the operands since we need to use the original ones for
@@ -3339,8 +3344,11 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_,
       /* Adjust *ref from the new operands.  */
       ao_ref rhs1_ref;
       ao_ref_init (&rhs1_ref, rhs1);
-      if (!ao_ref_init_from_vn_reference (&r, ao_ref_alias_set (&rhs1_ref),
-                                         ao_ref_base_alias_set (&rhs1_ref),
+      if (!ao_ref_init_from_vn_reference (&r,
+                                         force_no_tbaa ? 0
+                                         : ao_ref_alias_set (&rhs1_ref),
+                                         force_no_tbaa ? 0
+                                         : ao_ref_base_alias_set (&rhs1_ref),
                                          vr->type, vr->operands))
        return (void *)-1;
       /* This can happen with bitfields.  */