sra: Fix corner case of total scalarization with virtual inheritance (PR 102505)

PR 102505 is a situation where of SRA takes its initial top-level
access size from a get_ref_base_and_extent called on a COMPONENT_REF,
and thus derived frm the FIELD_DECL, which however does not include a
virtual base.  Total scalarization then goes on traversing the type,
which however has virtual base past the non-virtual bits, tricking SRA
to create sub-accesses outside of the supposedly encompassing
accesses, which in turn triggers the verifier within the pass.

The patch below fixes that by failing total scalarization when this
situation is detected.

gcc/ChangeLog:

2021-10-20  Martin Jambor  <mjambor@suse.cz>

	PR tree-optimization/102505
	* tree-sra.c (totally_scalarize_subtree): Check that the
	encountered field fits within the acces we would like to put it
	in.

gcc/testsuite/ChangeLog:

2021-10-20  Martin Jambor  <mjambor@suse.cz>

	PR tree-optimization/102505
	* g++.dg/torture/pr102505.C: New test.

diff --git a/gcc/testsuite/g++.dg/torture/pr102505.C b/gcc/testsuite/g++.dg/torture/pr102505.C
new file mode 100644 (file)
index 0000000..a846751
--- /dev/null
+++ b/gcc/testsuite/g++.dg/torture/pr102505.C
@@ -0,0 +1,15 @@
+struct D  { int i;  int pad alignas(16); };
+struct B : virtual D
+{
+  int j =84;
+  int k =84;
+};
+
+struct C: B { };
+
+int main()
+{
+  C c;
+  if (c.j != 84 || c.k != 84)
+    __builtin_abort();
+}

diff --git a/gcc/tree-sra.c b/gcc/tree-sra.c
index 9b786e2..f561e1a 100644 (file)
--- a/gcc/tree-sra.c
+++ b/gcc/tree-sra.c
@@ -3288,6 +3288,8 @@ totally_scalarize_subtree (struct access *root)
              continue;
 
            HOST_WIDE_INT pos = root->offset + int_bit_position (fld);
+           if (pos + fsize > root->size)
+             return false;
            enum total_sra_field_state
              state = total_should_skip_creating_access (root,
                                                         &last_seen_sibling,