Hi!
The following testcase is miscompiled, because expand_mult_const adds an
incorrect REG_EQUAL note to a temporary pseudo. In the testcase, we
do an unsigned __int128 multiplication of a variable by
0x7fffffffffffffff, which is determined to be best performed as
shift left by 63 (multiplication by 0x8000000000000000U) followed by
subtraction, i.e. (x << 63) - x. The val_so_far is tracked in an UHWI and
is necessarily always non-negative even because the caller ensures that,
if (is_neg && mode_bitsize > HOST_BITS_PER_WIDE_INT) then it performs
expand_mult_const on the negation and negates afterwards the result.
The problem is that it calls gen_int_mode, where the argument is signed hwi
(well, these days poly_int64). That is fine for DImode multiplication, we
don't really care about bits above the mode, but for TImode multiplication
it is significant. Without this patch we emit in that case:
(expr_list:REG_EQUAL (mult:TI (reg/v:TI 85 [ x ])
(const_int -9223372036854775808 [0x8000000000000000]))
but that is for TImode actually multiplication by
0xffffffffffffffff8000000000000000
rather than
0x00000000000000008000000000000000, so we need to emit
(const_wide_int 0x08000000000000000)
instead. Bootstrapped/regtested on x86_64-linux and i686-linux, ok for
trunk and after a while for 8.3?
2018-08-30 Jakub Jelinek <ja...@redhat.com>
PR middle-end/87138
* expmed.c (expand_mult_const): If val_so_far has MSB set, use
immed_wide_int_const instead of gen_int_mode. Formatting fixes.
* gcc.target/i386/avx512bw-pr87138.c: New test.
--- gcc/expmed.c.jj 2018-08-29 14:20:53.427109187 +0200
+++ gcc/expmed.c 2018-08-29 17:22:52.416860714 +0200
@@ -3347,19 +3347,27 @@ expand_mult_const (machine_mode mode, rt
/* Write a REG_EQUAL note on the last insn so that we can cse
multiplication sequences. Note that if ACCUM is a SUBREG,
we've set the inner register and must properly indicate that. */
- tem = op0, nmode = mode;
- accum_inner = accum;
- if (GET_CODE (accum) == SUBREG)
+ tem = op0, nmode = mode;
+ accum_inner = accum;
+ if (GET_CODE (accum) == SUBREG)
{
accum_inner = SUBREG_REG (accum);
nmode = GET_MODE (accum_inner);
tem = gen_lowpart (nmode, op0);
}
- insn = get_last_insn ();
- set_dst_reg_note (insn, REG_EQUAL,
- gen_rtx_MULT (nmode, tem,
- gen_int_mode (val_so_far, nmode)),
+ insn = get_last_insn ();
+ rtx c;
+ if (val_so_far > (unsigned HOST_WIDE_INT) HOST_WIDE_INT_MAX)
+ {
+ wide_int wval_so_far
+ = wi::uhwi (val_so_far,
+ GET_MODE_PRECISION (as_a <scalar_mode> (nmode)));
+ c = immed_wide_int_const (wval_so_far, nmode);
+ }
+ else
+ c = gen_int_mode (val_so_far, nmode);
+ set_dst_reg_note (insn, REG_EQUAL, gen_rtx_MULT (nmode, tem, c),
accum_inner);
}
}
--- gcc/testsuite/gcc.target/i386/avx512bw-pr87138.c.jj 2018-08-29
17:55:08.550154082 +0200
+++ gcc/testsuite/gcc.target/i386/avx512bw-pr87138.c 2018-08-29
17:56:11.112131910 +0200
@@ -0,0 +1,29 @@
+/* PR middle-end/87138 */
+/* { dg-do run { target int128 } } */
+/* { dg-options "-O -fno-tree-fre -mavx512bw -mtune=k8" } */
+/* { dg-require-effective-target avx512bw } */
+
+#include "avx512bw-check.h"
+
+typedef int U __attribute__ ((vector_size (64)));
+typedef __int128 V __attribute__ ((vector_size (64)));
+V g, i;
+
+static inline void
+foo (unsigned h, V j, U k, V n)
+{
+ k /= h;
+ __builtin_memmove (&h, &n, 1);
+ n[j[1]] *= 0x7FFFFFFFFFFFFFFF;
+ j[k[5]] = 0;
+ g = n;
+ i = h + j + n;
+}
+
+void
+avx512bw_test ()
+{
+ foo (~0, (V) { }, (U) { 5 }, (V) { 3 });
+ if (g[0] != (__int128) 3 * 0x7FFFFFFFFFFFFFFF)
+ abort ();
+}
Jakub
