[PATCH] tree-optimization/111019 - invariant motion and aliasing

[PATCH] tree-optimization/111019 - invariant motion and aliasing

[Richard Biener]

The following fixes a bad choice in representing things to the alias
oracle by LIM which while correct in pieces is inconsistent with itself.
When canonicalizing a ref to a bare deref instead of leaving the base
object and the extracted offset the same and just substituting an
alternate ref the following replaces the base and the offset as well,
avoiding the confusion that otherwise will arise in
aliasing_matching_component_refs_p.

Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed to trunk 
sofar.

Richard.

	PR tree-optimization/111019
	* tree-ssa-loop-im.cc (gather_mem_refs_stmt): When canonicalizing
	also scrap base and offset in case the ref is indirect.

	* g++.dg/torture/pr111019.C: New testcase.
---
 gcc/testsuite/g++.dg/torture/pr111019.C | 65 +++++++++++++++++++++++++
 gcc/tree-ssa-loop-im.cc                 | 14 +++++-
 2 files changed, 77 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/torture/pr111019.C

diff --git a/gcc/testsuite/g++.dg/torture/pr111019.C b/gcc/testsuite/g++.dg/torture/pr111019.C
new file mode 100644
index 00000000000..ce21a311c96
--- /dev/null
+++ b/gcc/testsuite/g++.dg/torture/pr111019.C
@@ -0,0 +1,65 @@
+// { dg-do run }
+// { dg-additional-options "-fstrict-aliasing" }
+
+#include <cassert>
+#include <memory>
+#include <string>
+
+class Base
+{
+public:
+  Base* previous = nullptr;
+  Base* next = nullptr;
+  Base* target = nullptr;
+};
+
+class Target : public Base
+{
+public:
+  __attribute__((always_inline)) ~Target()
+  {
+    while (this->next)
+    {
+      Base* n = this->next;
+
+      if (n->previous)
+        n->previous->next = n->next;
+      if (n->next)
+        n->next->previous = n->previous;
+      n->previous = nullptr;
+      n->next = nullptr;
+      n->target = nullptr;
+    }
+  }
+};
+
+template <typename T>
+class TargetWithData final : public Target
+{
+public:
+  TargetWithData(T data)
+    : data(data)
+  {}
+  T data;
+};
+
+void test()
+{
+  printf("test\n");
+  Base ptr;
+  {
+    auto data = std::make_unique<TargetWithData<std::string>>(std::string("asdf"));
+    ptr.target = &*data;
+    ptr.previous = &*data;
+    data->next = &ptr;
+
+    assert(ptr.target != nullptr);
+  }
+  assert(ptr.target == nullptr);
+}
+
+int main(int, char**)
+{
+  test();
+  return 0;
+}
diff --git a/gcc/tree-ssa-loop-im.cc b/gcc/tree-ssa-loop-im.cc
index 268f466bdc9..b8e33a4d49a 100644
--- a/gcc/tree-ssa-loop-im.cc
+++ b/gcc/tree-ssa-loop-im.cc
@@ -1665,11 +1665,21 @@ gather_mem_refs_stmt (class loop *loop, gimple *stmt)
 				     unshare_expr (mem_base));
 		  if (TYPE_ALIGN (ref_type) != ref_align)
 		    ref_type = build_aligned_type (ref_type, ref_align);
-		  (*slot)->mem.ref
+		  tree new_ref
 		    = fold_build2 (MEM_REF, ref_type, tmp,
 				   build_int_cst (ref_alias_type, mem_off));
 		  if ((*slot)->mem.volatile_p)
-		    TREE_THIS_VOLATILE ((*slot)->mem.ref) = 1;
+		    TREE_THIS_VOLATILE (new_ref) = 1;
+		  (*slot)->mem.ref = new_ref;
+		  /* Make sure the recorded base and offset are consistent
+		     with the newly built ref.  */
+		  if (TREE_CODE (TREE_OPERAND (new_ref, 0)) == ADDR_EXPR)
+		    ;
+		  else
+		    {
+		      (*slot)->mem.base = new_ref;
+		      (*slot)->mem.offset = 0;
+		    }
 		  gcc_checking_assert (TREE_CODE ((*slot)->mem.ref) == MEM_REF
 				       && is_gimple_mem_ref_addr
 				            (TREE_OPERAND ((*slot)->mem.ref,
-- 
2.35.3