bitintlower: Fix up ?ROTATE_EXPR lowering [PR117847]
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Commit Message
Hi!
In the ?ROTATE_EXPR lowering I forgot to handle rotation by 0 correctly.
INTEGER_CST 0 is very unlikely, it would be probably folded away, but
a non-constant count can't use just p - n because then the shift count
is out of bounds for zero.
In the FE I use n == 0 ? x : (x << n) | (x >> (p - n)) but bitintlower
here isn't prepared at this point to have bb split and am not sure if
using COND_EXPR is a good idea either, so the patch uses (p - n) % p.
Perhaps I should just disable lowering the rotate in the FE for the
non-mode precision BITINT_TYPEs too.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2024-12-03 Jakub Jelinek <jakub@redhat.com>
PR middle-end/117847
* gimple-lower-bitint.cc (gimple_lower_bitint) <case LROTATE_EXPR>:
Use m = (p - n) % p instead of m = p - n for the other shift count.
* gcc.dg/torture/bitint-75.c: New test.
Jakub
Comments
On Tue, 3 Dec 2024, Jakub Jelinek wrote:
> Hi!
>
> In the ?ROTATE_EXPR lowering I forgot to handle rotation by 0 correctly.
> INTEGER_CST 0 is very unlikely, it would be probably folded away, but
> a non-constant count can't use just p - n because then the shift count
> is out of bounds for zero.
>
> In the FE I use n == 0 ? x : (x << n) | (x >> (p - n)) but bitintlower
> here isn't prepared at this point to have bb split and am not sure if
> using COND_EXPR is a good idea either, so the patch uses (p - n) % p.
> Perhaps I should just disable lowering the rotate in the FE for the
> non-mode precision BITINT_TYPEs too.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
OK.
Richard.
> 2024-12-03 Jakub Jelinek <jakub@redhat.com>
>
> PR middle-end/117847
> * gimple-lower-bitint.cc (gimple_lower_bitint) <case LROTATE_EXPR>:
> Use m = (p - n) % p instead of m = p - n for the other shift count.
>
> * gcc.dg/torture/bitint-75.c: New test.
>
> --- gcc/gimple-lower-bitint.cc.jj 2024-11-23 13:00:29.000000000 +0100
> +++ gcc/gimple-lower-bitint.cc 2024-12-03 00:50:58.839052842 +0100
> @@ -6233,11 +6233,20 @@ gimple_lower_bitint (void)
> tree p = build_int_cst (TREE_TYPE (n),
> TYPE_PRECISION (type));
> if (TREE_CODE (n) == INTEGER_CST)
> - m = fold_build2 (MINUS_EXPR, TREE_TYPE (n), p, n);
> + {
> + if (integer_zerop (n))
> + m = n;
> + else
> + m = fold_build2 (MINUS_EXPR, TREE_TYPE (n), p, n);
> + }
> else
> {
> + tree tem = make_ssa_name (TREE_TYPE (n));
> + g = gimple_build_assign (tem, MINUS_EXPR, p, n);
> + gsi_insert_before (&gsi, g, GSI_SAME_STMT);
> + gimple_set_location (g, loc);
> m = make_ssa_name (TREE_TYPE (n));
> - g = gimple_build_assign (m, MINUS_EXPR, p, n);
> + g = gimple_build_assign (m, TRUNC_MOD_EXPR, tem, p);
> gsi_insert_before (&gsi, g, GSI_SAME_STMT);
> gimple_set_location (g, loc);
> }
> --- gcc/testsuite/gcc.dg/torture/bitint-75.c.jj 2024-12-02 11:51:52.448594565 +0100
> +++ gcc/testsuite/gcc.dg/torture/bitint-75.c 2024-12-02 11:51:43.387722691 +0100
> @@ -0,0 +1,27 @@
> +/* PR middle-end/117847 */
> +/* { dg-do run { target bitint } } */
> +/* { dg-options "-std=c23" } */
> +/* { dg-skip-if "" { ! run_expensive_tests } { "*" } { "-O0" "-O2" } } */
> +/* { dg-skip-if "" { ! run_expensive_tests } { "-flto" } { "" } } */
> +
> +#if __BITINT_MAXWIDTH__ >= 512
> +typedef unsigned _BitInt(512) B;
> +
> +__attribute__((noipa)) B
> +foo (B a, int r)
> +{
> + B b = __builtin_stdc_rotate_left (a, r);
> + return b;
> +}
> +#endif
> +
> +int
> +main ()
> +{
> +#if __BITINT_MAXWIDTH__ >= 512
> + B a = 0x4ad4fdecc8717d7c6f8b1afb82fdb742477ef2ab34057d1dcc79ba30c38a352dea3253c8c25126d98da02213ad54b90d2998f947941ea4b45e71c61dc1fe3192uwb;
> + B x = foo (a, 0);
> + if (x != a)
> + __builtin_abort ();
> +#endif
> +}
>
> Jakub
>
>
@@ -6233,11 +6233,20 @@ gimple_lower_bitint (void)
tree p = build_int_cst (TREE_TYPE (n),
TYPE_PRECISION (type));
if (TREE_CODE (n) == INTEGER_CST)
- m = fold_build2 (MINUS_EXPR, TREE_TYPE (n), p, n);
+ {
+ if (integer_zerop (n))
+ m = n;
+ else
+ m = fold_build2 (MINUS_EXPR, TREE_TYPE (n), p, n);
+ }
else
{
+ tree tem = make_ssa_name (TREE_TYPE (n));
+ g = gimple_build_assign (tem, MINUS_EXPR, p, n);
+ gsi_insert_before (&gsi, g, GSI_SAME_STMT);
+ gimple_set_location (g, loc);
m = make_ssa_name (TREE_TYPE (n));
- g = gimple_build_assign (m, MINUS_EXPR, p, n);
+ g = gimple_build_assign (m, TRUNC_MOD_EXPR, tem, p);
gsi_insert_before (&gsi, g, GSI_SAME_STMT);
gimple_set_location (g, loc);
}
@@ -0,0 +1,27 @@
+/* PR middle-end/117847 */
+/* { dg-do run { target bitint } } */
+/* { dg-options "-std=c23" } */
+/* { dg-skip-if "" { ! run_expensive_tests } { "*" } { "-O0" "-O2" } } */
+/* { dg-skip-if "" { ! run_expensive_tests } { "-flto" } { "" } } */
+
+#if __BITINT_MAXWIDTH__ >= 512
+typedef unsigned _BitInt(512) B;
+
+__attribute__((noipa)) B
+foo (B a, int r)
+{
+ B b = __builtin_stdc_rotate_left (a, r);
+ return b;
+}
+#endif
+
+int
+main ()
+{
+#if __BITINT_MAXWIDTH__ >= 512
+ B a = 0x4ad4fdecc8717d7c6f8b1afb82fdb742477ef2ab34057d1dcc79ba30c38a352dea3253c8c25126d98da02213ad54b90d2998f947941ea4b45e71c61dc1fe3192uwb;
+ B x = foo (a, 0);
+ if (x != a)
+ __builtin_abort ();
+#endif
+}