Fix value numbering dealing with reverse byte order

Hi,
  While working on bit-field lowering pass, I came across this bug.
The IR looks like:
  VIEW_CONVERT_EXPR<unsigned long>(var1) = _12;
  _1 = BIT_FIELD_REF <var1, 64, 0>;

Where the BIT_FIELD_REF has REF_REVERSE_STORAGE_ORDER set on it
and var1's type has TYPE_REVERSE_STORAGE_ORDER set on it.
PRE/FRE would decided to prop _12 into the BFR statement
which would produce wrong code.
And yes _12 has the correct byte order already; bit-field lowering
removes the implicit byte swaps in the IR and adds the explicity
to make it easier optimize later on.

This patch adds a check for storage_order_barrier_p on the lhs tree
which returns true in the case where we had a reverse order with a VCE.

ChangeLog:
* tree-ssa-sccvn.c(vn_reference_lookup_3): Check lhs for
!storage_order_barrier_p.

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index bbb7e06c7fb36f51f6ed3f58ac53183e08e6bac9..7baf474abb824721a8278e16743f77902681ef1e 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2020-01-16  Andrew Pinski  <apinski@marvell.com>
+
+       * tree-ssa-sccvn.c(vn_reference_lookup_3): Check lhs for
+       !storage_order_barrier_p.
+
 2020-01-16  Andrew Pinski  <apinski@marvell.com>
 
        * sched-int.h (_dep): Add unused bit-field field for the padding.

diff --git a/gcc/tree-ssa-sccvn.c b/gcc/tree-ssa-sccvn.c
index 3b27c50ef7546f703ff877fe9e9c2855ca294296..4d1301593d7edcf14689b71403453cd05402151a 100644 (file)
--- a/gcc/tree-ssa-sccvn.c
+++ b/gcc/tree-ssa-sccvn.c
@@ -2593,6 +2593,7 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_,
                                         &offset2, &size2, &maxsize2, &reverse);
       if (base2
          && !reverse
+         && !storage_order_barrier_p (lhs)
          && known_eq (maxsize2, size2)
          && multiple_p (size2, BITS_PER_UNIT)
          && multiple_p (offset2, BITS_PER_UNIT)
@@ -2695,6 +2696,7 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_,
                                         &offset2, &size2, &maxsize2, &reverse);
       tree def_rhs = gimple_assign_rhs1 (def_stmt);
       if (!reverse
+         && !storage_order_barrier_p (lhs)
          && known_size_p (maxsize2)
          && known_eq (maxsize2, size2)
          && adjust_offsets_for_equal_base_address (base, &offset,