[PATCH] Fix expansion of comparisons into signed type with 1-bit precision (PR middle-end/48973)

[Jakub Jelinek]

Hi!

The read from a 1-bit signed bitfield initialized by a comparison
is optimized into the comparison, which has that 1-bit signed bitfield
comparison.  Unfortunately that is still expanded as setting the result
to 0 resp. 1 instead of this case 0 resp. -1 QImode pseudo, which is then
sign extended into SImode for the comparison.

Fixed by special casing expansion in that case.  I think it is rare enough
we can just ignore the fold_single_bit_test optimization in that case,
rather than having two versions thereof.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk/4.6?

2011-05-12  Jakub Jelinek  <ja...@redhat.com>

        PR middle-end/48973
        * expr.c (expand_expr_real_2) <case LT_EXPR>: If do_store_flag
        failed and the comparison has a single bit signed type, use
        constm1_rtx instead of const1_rtx for true value.
        (do_store_flag): If ops->type is single bit signed type, disable
        signel bit test optimization and pass -1 instead of 1 as last
        parameter to emit_store_flag_force.

        * gcc.c-torture/execute/pr48973-1.c: New test.
        * gcc.c-torture/execute/pr48973-2.c: New test.

--- gcc/expr.c.jj       2011-05-11 19:39:04.000000000 +0200
+++ gcc/expr.c  2011-05-12 10:46:52.000000000 +0200
@@ -8105,7 +8105,10 @@ expand_expr_real_2 (sepops ops, rtx targ
       op1 = gen_label_rtx ();
       jumpifnot_1 (code, treeop0, treeop1, op1, -1);
 
-      emit_move_insn (target, const1_rtx);
+      if (TYPE_PRECISION (type) == 1 && !TYPE_UNSIGNED (type))
+       emit_move_insn (target, constm1_rtx);
+      else
+       emit_move_insn (target, const1_rtx);
 
       emit_label (op1);
       return target;
@@ -10050,7 +10053,8 @@ do_store_flag (sepops ops, rtx target, e
 
   if ((code == NE || code == EQ)
       && TREE_CODE (arg0) == BIT_AND_EXPR && integer_zerop (arg1)
-      && integer_pow2p (TREE_OPERAND (arg0, 1)))
+      && integer_pow2p (TREE_OPERAND (arg0, 1))
+      && (TYPE_PRECISION (ops->type) != 1 || TYPE_UNSIGNED (ops->type)))
     {
       tree type = lang_hooks.types.type_for_mode (mode, unsignedp);
       return expand_expr (fold_single_bit_test (loc,
@@ -10070,7 +10074,9 @@ do_store_flag (sepops ops, rtx target, e
 
   /* Try a cstore if possible.  */
   return emit_store_flag_force (target, code, op0, op1,
-                               operand_mode, unsignedp, 1);
+                               operand_mode, unsignedp,
+                               (TYPE_PRECISION (ops->type) == 1
+                                && !TYPE_UNSIGNED (ops->type)) ? -1 : 1);
 }
 
 
--- gcc/testsuite/gcc.c-torture/execute/pr48973-1.c.jj  2011-05-12 
10:53:49.000000000 +0200
+++ gcc/testsuite/gcc.c-torture/execute/pr48973-1.c     2011-05-12 
10:53:12.000000000 +0200
@@ -0,0 +1,20 @@
+/* PR middle-end/48973 */
+
+extern void abort (void);
+struct S { int f : 1; } s;
+int v = -1;
+
+void
+foo (unsigned int x)
+{
+  if (x != -1U)
+    abort ();
+}
+
+int
+main ()
+{
+  s.f = (v & 1) > 0;
+  foo (s.f);
+  return 0;
+}
--- gcc/testsuite/gcc.c-torture/execute/pr48973-2.c.jj  2011-05-12 
10:53:52.000000000 +0200
+++ gcc/testsuite/gcc.c-torture/execute/pr48973-2.c     2011-05-12 
10:53:37.000000000 +0200
@@ -0,0 +1,14 @@
+/* PR middle-end/48973 */
+
+extern void abort (void);
+struct S { int f : 1; } s;
+int v = -1;
+
+int
+main ()
+{
+  s.f = v < 0;
+  if ((unsigned int) s.f != -1U)
+    abort ();
+  return 0;
+}

        Jakub