Hi!
When val_so_far is signed, we can end up in UB in various places, e.g.
for the multiplication by 0x7fffffffffffffff, which is done as << 63 shift
followed by subtracting one.
Fixed by computing this in UHWI instead, and only cast at the end to SHWI.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2016-08-16 Jakub Jelinek <ja...@redhat.com>
PR middle-end/67485
* expmed.c (expand_mult_const): Change val_so_far's type to UHWI,
only cast it to SHWI for the final comparison.
* gcc.c-torture/compile/pr67485.c: New test.
--- gcc/expmed.c.jj 2016-08-12 17:33:46.000000000 +0200
+++ gcc/expmed.c 2016-08-15 13:45:59.197300977 +0200
@@ -3055,7 +3055,7 @@ expand_mult_const (machine_mode mode, rt
rtx target, const struct algorithm *alg,
enum mult_variant variant)
{
- HOST_WIDE_INT val_so_far;
+ unsigned HOST_WIDE_INT val_so_far;
rtx_insn *insn;
rtx accum, tem;
int opno;
@@ -3105,14 +3105,14 @@ expand_mult_const (machine_mode mode, rt
tem = expand_shift (LSHIFT_EXPR, mode, op0, log, NULL_RTX, 0);
accum = force_operand (gen_rtx_PLUS (mode, accum, tem),
add_target ? add_target : accum_target);
- val_so_far += HOST_WIDE_INT_1 << log;
+ val_so_far += HOST_WIDE_INT_1U << log;
break;
case alg_sub_t_m2:
tem = expand_shift (LSHIFT_EXPR, mode, op0, log, NULL_RTX, 0);
accum = force_operand (gen_rtx_MINUS (mode, accum, tem),
add_target ? add_target : accum_target);
- val_so_far -= HOST_WIDE_INT_1 << log;
+ val_so_far -= HOST_WIDE_INT_1U << log;
break;
case alg_add_t2_m:
@@ -3188,7 +3188,7 @@ expand_mult_const (machine_mode mode, rt
nmode = GET_MODE_INNER (mode);
val &= GET_MODE_MASK (nmode);
val_so_far &= GET_MODE_MASK (nmode);
- gcc_assert (val == val_so_far);
+ gcc_assert (val == (HOST_WIDE_INT) val_so_far);
return accum;
}
--- gcc/testsuite/gcc.c-torture/compile/pr67485.c.jj 2016-08-15
13:48:13.747639954 +0200
+++ gcc/testsuite/gcc.c-torture/compile/pr67485.c 2016-08-15
13:48:17.113598401 +0200
@@ -0,0 +1,7 @@
+/* PR middle-end/67485 */
+
+long int
+foo (long int x)
+{
+ return x * __LONG_MAX__;
+}
Jakub
