[PATCH] ifcvt: Don't lower bitfields with non-constant offsets [PR 111882]

[Andre Vieira (lists)]

Hi,

This patch stops lowering of bitfields by ifcvt when they have non-constant
offsets as we are not likely to be able to do anything useful with those 
during
vectorization.  That also fixes the issue reported in PR 111882, which was
being caused by an offset with a side-effect being lowered, but 
constants have
no side-effects so we will no longer run into that problem.
Bootstrapped and regression tested on aarch64-unknown-linux-gnu.

OK for trunk?

gcc/ChangeLog:

        PR tree-optimization/111882
        * tree-if-conv.cc (get_bitfield_rep): Return NULL_TREE for bitfields 
with
        non-constant offsets.

gcc/testsuite/ChangeLog:

        * gcc.dg/vect/pr111882.c: New test.diff --git a/gcc/testsuite/gcc.dg/vect/pr111882.c 
b/gcc/testsuite/gcc.dg/vect/pr111882.c
new file mode 100644
index 
0000000000000000000000000000000000000000..024ad57b6930dd1f516e9c8127e2b440016360c6
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr111882.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-additional-options { -fdump-tree-ifcvt-all } } */
+
+static void __attribute__((noipa)) f(int n) {
+  int i, j;
+  struct S { char d[n]; int a; int b : 17; int c : 12; };
+  struct S A[100][1111];
+  for (i = 0; i < 100; i++) {
+    asm volatile("" : : "g"(&A[0][0]) : "memory");
+    for (j = 0; j < 1111; j++) A[i][j].b = 2;
+  }
+}
+void g(void) { f(1); }
+
+/* { dg-final { scan-tree-dump-not "Bitfield OK to lower" "ifcvt" } } */
diff --git a/gcc/tree-if-conv.cc b/gcc/tree-if-conv.cc
index 
dab7eeb7707ae8f1f342a571f8e5c99e0ef39309..66f3c882cb688049224b344b81637e7b1ae7e36c
 100644
--- a/gcc/tree-if-conv.cc
+++ b/gcc/tree-if-conv.cc
@@ -3495,6 +3495,7 @@ get_bitfield_rep (gassign *stmt, bool write, tree *bitpos,
                        : gimple_assign_rhs1 (stmt);
 
   tree field_decl = TREE_OPERAND (comp_ref, 1);
+  tree ref_offset = component_ref_field_offset (comp_ref);
   tree rep_decl = DECL_BIT_FIELD_REPRESENTATIVE (field_decl);
 
   /* Bail out if the representative is not a suitable type for a scalar
@@ -3509,6 +3510,12 @@ get_bitfield_rep (gassign *stmt, bool write, tree 
*bitpos,
   if (compare_tree_int (DECL_SIZE (field_decl), bf_prec) != 0)
     return NULL_TREE;
 
+  if (!TREE_CONSTANT (DECL_FIELD_OFFSET (rep_decl))
+      || !TREE_CONSTANT (DECL_FIELD_BIT_OFFSET (rep_decl))
+      || !TREE_CONSTANT (ref_offset)
+      || !TREE_CONSTANT (DECL_FIELD_BIT_OFFSET (field_decl)))
+    return NULL_TREE;
+
   if (struct_expr)
     *struct_expr = TREE_OPERAND (comp_ref, 0);
 
@@ -3529,7 +3536,7 @@ get_bitfield_rep (gassign *stmt, bool write, tree *bitpos,
         the structure and the container from the number of bits from the start
         of the structure and the actual bitfield member. */
       tree bf_pos = fold_build2 (MULT_EXPR, bitsizetype,
-                                DECL_FIELD_OFFSET (field_decl),
+                                ref_offset,
                                 build_int_cst (bitsizetype, BITS_PER_UNIT));
       bf_pos = fold_build2 (PLUS_EXPR, bitsizetype, bf_pos,
                            DECL_FIELD_BIT_OFFSET (field_decl));