From: Andre Vieira <andre.simoesdiasvieira@arm.com>
Date: Fri, 20 Oct 2023 16:02:32 +0000 (+0100)
Subject: ifcvt: Don't lower bitfields with non-constant offsets [PR 111882]
X-Git-Tag: releases/gcc-13.3.0~103
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=4950f6bcd3cce9deb630b76af42cd6d6968ba03f;p=thirdparty%2Fgcc.git

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

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.

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.

(cherry picked from commit 24cf1f600b8ad34c68a51f48884e72d01f729893)
---

diff --git a/gcc/testsuite/gcc.dg/vect/pr111882.c b/gcc/testsuite/gcc.dg/vect/pr111882.c
new file mode 100644
index 000000000000..024ad57b6930
--- /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 a19450f533da..fddc4a890c69 100644
--- a/gcc/tree-if-conv.cc
+++ b/gcc/tree-if-conv.cc
@@ -3330,6 +3330,7 @@ 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
@@ -3344,6 +3345,15 @@ 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_CODE (DECL_FIELD_OFFSET (rep_decl)) != INTEGER_CST
+      || TREE_CODE (ref_offset) != INTEGER_CST)
+    {
+      if (dump_file && (dump_flags & TDF_DETAILS))
+	fprintf (dump_file, "\t Bitfield NOT OK to lower,"
+			    " offset is non-constant.\n");
+      return NULL_TREE;
+    }
+
   if (struct_expr)
     *struct_expr = TREE_OPERAND (comp_ref, 0);
 
@@ -3364,7 +3374,7 @@ 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));