On Tue, Mar 15, 2016 at 01:08:50PM +0100, Bernd Schmidt wrote:
> This looks really specialized, and I'd be worrying about whether it really
> is the right condition. Where exactly was the constant shifted by 31 and
> count set to 0? Must be here, right?
Yes, it is that spot.
>
> /* If we have (A << B << C) for any shift, we can convert this to
> (A << C << B). This wins if A is a constant. Only try this if
> B is not a constant. */
>
> else if (GET_CODE (varop) == code
> && CONST_INT_P (XEXP (varop, 0))
> && !CONST_INT_P (XEXP (varop, 1)))
> {
> rtx new_rtx = simplify_const_binary_operation (code, mode,
> XEXP (varop, 0),
> GEN_INT (count));
> varop = gen_rtx_fmt_ee (code, mode, new_rtx, XEXP (varop, 1));
> count = 0;
> continue;
> }
>
> I think it might be clearer to notice and fix the problem here (or set a
> need_mask flag).
So do you prefer this instead?
2016-03-15 Jakub Jelinek <ja...@redhat.com>
PR rtl-optimization/70222
* combine.c (simplify_shift_const_1): For A >> B >> C LSHIFTRT
optimization if mode is different from result_mode, queue up masking
of the result in outer_op. Formatting fix.
* gcc.c-torture/execute/pr70222-1.c: New test.
* gcc.c-torture/execute/pr70222-2.c: New test.
--- gcc/combine.c.jj 2016-03-14 23:18:37.958408627 +0100
+++ gcc/combine.c 2016-03-15 14:08:34.754434506 +0100
@@ -10524,9 +10524,19 @@ simplify_shift_const_1 (enum rtx_code co
&& CONST_INT_P (XEXP (varop, 0))
&& !CONST_INT_P (XEXP (varop, 1)))
{
+ /* For ((unsigned) (cstULL >> count)) >> cst2 we have to make
+ sure the result will be masked. See PR70222. */
+ if (code == LSHIFTRT
+ && mode != result_mode
+ && !merge_outer_ops (&outer_op, &outer_const, AND,
+ GET_MODE_MASK (result_mode)
+ >> orig_count, result_mode,
+ &complement_p))
+ break;
+
rtx new_rtx = simplify_const_binary_operation (code, mode,
- XEXP (varop, 0),
- GEN_INT (count));
+ XEXP (varop, 0),
+ GEN_INT (count));
varop = gen_rtx_fmt_ee (code, mode, new_rtx, XEXP (varop, 1));
count = 0;
continue;
--- gcc/testsuite/gcc.c-torture/execute/pr70222-1.c.jj 2016-03-15
11:30:41.657000384 +0100
+++ gcc/testsuite/gcc.c-torture/execute/pr70222-1.c 2016-03-15
11:30:41.657000384 +0100
@@ -0,0 +1,30 @@
+/* PR rtl-optimization/70222 */
+
+int a = 1;
+unsigned int b = 2;
+int c = 0;
+int d = 0;
+
+void
+foo ()
+{
+ int e = ((-(c >= c)) < b) > ((int) (-1ULL >> ((a / a) * 15)));
+ d = -e;
+}
+
+__attribute__((noinline, noclone)) void
+bar (int x)
+{
+ if (x != -1)
+ __builtin_abort ();
+}
+
+int
+main ()
+{
+#if __CHAR_BIT__ == 8 && __SIZEOF_INT__ == 4 && __SIZEOF_LONG_LONG__ == 8
+ foo ();
+ bar (d);
+#endif
+ return 0;
+}
--- gcc/testsuite/gcc.c-torture/execute/pr70222-2.c.jj 2016-03-15
11:36:13.273366841 +0100
+++ gcc/testsuite/gcc.c-torture/execute/pr70222-2.c 2016-03-15
11:36:18.156298614 +0100
@@ -0,0 +1,20 @@
+/* PR rtl-optimization/70222 */
+
+#if __CHAR_BIT__ == 8 && __SIZEOF_INT__ == 4 && __SIZEOF_LONG_LONG__ == 8
+__attribute__((noinline, noclone)) unsigned int
+foo (int x)
+{
+ unsigned long long y = -1ULL >> x;
+ return (unsigned int) y >> 31;
+}
+#endif
+
+int
+main ()
+{
+#if __CHAR_BIT__ == 8 && __SIZEOF_INT__ == 4 && __SIZEOF_LONG_LONG__ == 8
+ if (foo (15) != 1 || foo (32) != 1 || foo (33) != 0)
+ __builtin_abort ();
+#endif
+ return 0;
+}
Jakub
