inchash::hash::add_wide_int operated directly on the raw encoding
of the wide_int, including any redundant upper bits. The problem
with that is that the upper bits are only defined for some wide-int
storage types (including wide_int itself). wi::to_wide(tree) instead
returns a value that is extended according to the signedness of the
type (so that wi::to_widest can use the same encoding) while rtxes
have the awkward special case of BI, which can be zero-extended
rather than sign-extended.
In the PR, we computed a hash for a "normal" sign-extended wide_int
while the existing entries hashed wi::to_wide(tree). This gives
different results for unsigned types that have the top bit set.
The patch fixes that by hashing the canonical sign-extended form even
if the raw encoding happens to be different.
Tested on aarch64-linux-gnu (with and without SVE), armeb-eabi
and x86_64-linux-gnu. OK to install?
Richard
2019-07-29 Richard Sandiford <richard.sandif...@arm.com>
gcc/
* wide-int.h (generic_wide_int::sext_elt): New function.
* inchash.h (hash::add_wide_int): Use it instead of elt.
Index: gcc/wide-int.h
===================================================================
--- gcc/wide-int.h 2019-07-10 19:41:26.391898059 +0100
+++ gcc/wide-int.h 2019-07-29 10:08:12.048610030 +0100
@@ -730,6 +730,7 @@ class GTY(()) generic_wide_int : public
/* Public accessors for the interior of a wide int. */
HOST_WIDE_INT sign_mask () const;
HOST_WIDE_INT elt (unsigned int) const;
+ HOST_WIDE_INT sext_elt (unsigned int) const;
unsigned HOST_WIDE_INT ulow () const;
unsigned HOST_WIDE_INT uhigh () const;
HOST_WIDE_INT slow () const;
@@ -909,6 +910,23 @@ generic_wide_int <storage>::elt (unsigne
return this->get_val ()[i];
}
+/* Like elt, but sign-extend beyond the upper bit, instead of returning
+ the raw encoding. */
+template <typename storage>
+inline HOST_WIDE_INT
+generic_wide_int <storage>::sext_elt (unsigned int i) const
+{
+ HOST_WIDE_INT elt_i = elt (i);
+ if (!is_sign_extended)
+ {
+ unsigned int precision = this->get_precision ();
+ unsigned int lsb = i * HOST_BITS_PER_WIDE_INT;
+ if (precision - lsb < HOST_BITS_PER_WIDE_INT)
+ elt_i = sext_hwi (elt_i, precision - lsb);
+ }
+ return elt_i;
+}
+
template <typename storage>
template <typename T>
inline generic_wide_int <storage> &
Index: gcc/inchash.h
===================================================================
--- gcc/inchash.h 2019-03-08 18:15:36.704740334 +0000
+++ gcc/inchash.h 2019-07-29 10:08:12.048610030 +0100
@@ -85,7 +85,7 @@ hashval_t iterative_hash_hashval_t (hash
{
add_int (x.get_len ());
for (unsigned i = 0; i < x.get_len (); i++)
- add_hwi (x.elt (i));
+ add_hwi (x.sext_elt (i));
}
/* Hash in pointer PTR. */
