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.

This backport also has commit f217e87972a2a207e793101fc05cfc9dd095c678
squashed into it in order to avoid PR 102886 that the fix introduced
on trunk.

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.

(cherry picked from commit 701ee067807b80957c65bd7ff94b6099a27181de)

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 8dfc923ed7e3b8558e818c13a9f48aa3e4aa8dbe..970ad386873b38b7e2dc526aa1b101dcee3d550e 100644 (file)
--- a/gcc/tree-sra.c
+++ b/gcc/tree-sra.c
@@ -3265,6 +3265,8 @@ totally_scalarize_subtree (struct access *root)
              continue;
 
            HOST_WIDE_INT pos = root->offset + int_bit_position (fld);
+           if (pos + fsize > root->offset + root->size)
+             return false;
            enum total_sra_field_state
              state = total_should_skip_creating_access (root,
                                                         &last_seen_sibling,