[gcc r12-4607] sra: Fix corner case of total scalarization with virtual inheritance (PR 102505)

[Martin Jambor <jamborm@gcc.gnu.org>]

https://gcc.gnu.org/g:701ee067807b80957c65bd7ff94b6099a27181de

commit r12-4607-g701ee067807b80957c65bd7ff94b6099a27181de
Author: Martin Jambor <mjambor@suse.cz>
Date:   Thu Oct 21 14:26:45 2021 +0200

    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:
---
 gcc/testsuite/g++.dg/torture/pr102505.C | 15 +++++++++++++++
 gcc/tree-sra.c                          |  2 ++
 2 files changed, 17 insertions(+)

diff --git a/gcc/testsuite/g++.dg/torture/pr102505.C b/gcc/testsuite/g++.dg/torture/pr102505.C
new file mode 100644
index 00000000000..a846751a0d6
--- /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 9b786e29e4e..f561e1a2133 100644
--- 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,