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.
Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed to trunk.
2022-06-30 Richard Biener <rguent...@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.
---
gcc/testsuite/g++.dg/torture/pr106131.C | 34 +++++++++++++++++++++++++
gcc/tree-ssa-sccvn.cc | 16 +++++++++---
2 files changed, 46 insertions(+), 4 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/torture/pr106131.C
diff --git a/gcc/testsuite/g++.dg/torture/pr106131.C
b/gcc/testsuite/g++.dg/torture/pr106131.C
new file mode 100644
index 00000000000..e110f4a8fe6
--- /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 9deedeac378..76d92895a3a 100644
--- 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. */
--
2.36.1
