[gcc r10-10249] sra: Fix corner case of total scalarization with virtual inheritance (PR 102505)

[gcc r10-10249] sra: Fix corner case of total scalarization with virtual inheritance (PR 102505)

[Martin Jambor]

https://gcc.gnu.org/g:7d398e42d3d4ded84cb7a86396c75c5aaf518283

commit r10-10249-g7d398e42d3d4ded84cb7a86396c75c5aaf518283
Author: Martin Jambor <mjambor@suse.cz>
Date:   Tue Nov 2 11:17:51 2021 +0100

    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:
---
 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 85b9cc9ed7f..09d951a261b 100644
--- 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,