tree-optimization/106922 - extend same-val clobber FRE

The following extends the skipping of same valued stores to
handle an arbitrary number of them as long as they are from the
same value (which we now record).  That's an obvious extension
which allows to optimize the m_engaged member of std::optional
more reliably.

	PR tree-optimization/106922
	* tree-ssa-sccvn.cc (vn_reference_lookup_3): Allow
	an arbitrary number of same valued skipped stores.

	* g++.dg/torture/pr106922.C: New testcase.

(cherry picked from commit af611afe5fcc908a6678b5b205fb5af7d64fbcb2)

diff --git a/gcc/testsuite/g++.dg/torture/pr106922.C b/gcc/testsuite/g++.dg/torture/pr106922.C
new file mode 100644 (file)
index 0000000..046fc6c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/torture/pr106922.C
@@ -0,0 +1,48 @@
+// { dg-do compile }
+// { dg-require-effective-target c++17 }
+// { dg-additional-options "-Wall" }
+// -O1 doesn't iterate VN and thus has bogus uninit diagnostics
+// { dg-skip-if "" { *-*-* } { "-O1" } { "" } }
+
+#include <vector>
+
+#include <optional>
+template <class T>
+using Optional = std::optional<T>;
+
+#include <sstream>
+
+struct MyOptionalStructWithInt {
+    int myint; /* works without this */
+    Optional<std::vector<std::string>> myoptional;
+};
+
+struct MyOptionalsStruct {
+    MyOptionalStructWithInt external1;
+    MyOptionalStructWithInt external2;
+};
+
+struct MyStruct { };
+std::ostream &operator << (std::ostream &os, const MyStruct &myStruct);
+
+std::vector<MyStruct> getMyStructs();
+
+void test()
+{
+    MyOptionalsStruct externals;
+    MyOptionalStructWithInt internal1;
+    MyOptionalStructWithInt internal2;
+
+    std::vector<MyStruct> myStructs;
+    myStructs = getMyStructs();
+
+    for (const auto& myStruct : myStructs)
+    {
+        std::stringstream address_stream;
+        address_stream << myStruct;
+        internal1.myint = internal2.myint = 0;
+        externals.external1 = internal1;
+        externals.external2 = internal2;
+        externals.external2 = internal2;
+    }
+}

diff --git a/gcc/tree-ssa-sccvn.cc b/gcc/tree-ssa-sccvn.cc
index cfacf609f434a415206120ae8c883ffe8e9dc376..854c0c25bc75341cf1d9f8f0c10bc8f8c8bfc558 100644 (file)
--- a/gcc/tree-ssa-sccvn.cc
+++ b/gcc/tree-ssa-sccvn.cc
@@ -2671,7 +2671,6 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_,
       if (is_gimple_reg_type (TREE_TYPE (lhs))
          && types_compatible_p (TREE_TYPE (lhs), vr->type)
          && (ref->ref || data->orig_ref.ref)
-         && !data->same_val
          && !data->mask
          && data->partial_defs.is_empty ()
          && multiple_p (get_object_alignment
@@ -2684,8 +2683,13 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_,
             a different loop iteration but only to loop invariants.  Use
             CONSTANT_CLASS_P (unvalueized!) as conservative approximation.
             The one-hop lookup below doesn't have this issue since there's
-            a virtual PHI before we ever reach a backedge to cross.  */
-         if (CONSTANT_CLASS_P (rhs))
+            a virtual PHI before we ever reach a backedge to cross.
+            We can skip multiple defs as long as they are from the same
+            value though.  */
+         if (data->same_val
+             && !operand_equal_p (data->same_val, rhs))
+           ;
+         else if (CONSTANT_CLASS_P (rhs))
            {
              if (dump_file && (dump_flags & TDF_DETAILS))
                {