Hi!
The following patch attempts to fix the (view_convert (convert@0 @1))
optimization. If TREE_TYPE (@0) is a _BitInt type with padding bits
and @0 has the same precision as @1 and it has a different sign
and _BitInt with padding bits are extended on the target (x86 doesn't,
aarch64 doesn't, but arm plans to do that), then optimizing it to
just (view_convert @1) is wrong, the padding bits wouldn't be what
it should be.
E.g. bitint-64.c test with -O2 has
_5 = (unsigned _BitInt(5)) _4;
_7 = (unsigned _BitInt(5)) e.0_1;
_8 = _5 + _7;
_9 = (_BitInt(5)) _8;
_10 = VIEW_CONVERT_EXPR<unsigned char>(_9);
and forwprop1 changes that to just
_5 = (unsigned _BitInt(5)) _4;
_7 = (unsigned _BitInt(5)) e.0_1;
_8 = _5 + _7;
_10 = VIEW_CONVERT_EXPR<unsigned char>(_8);
The former makes the padding bits well defined (at least on arm in
the future), while the latter has those bits zero extended.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2024-03-26 Jakub Jelinek <ja...@redhat.com>
PR tree-optimization/114469
* match.pd ((view_convert (convert@0 @1))): Don't optimize if
TREE_TYPE (@0) is a BITINT_TYPE with padding bits which are supposed
to be extended by the ABI.
--- gcc/match.pd.jj 2024-03-15 11:04:24.672914747 +0100
+++ gcc/match.pd 2024-03-26 15:49:44.177864509 +0100
@@ -4699,13 +4699,38 @@ (define_operator_list SYNC_FETCH_AND_AND
zero-extend while keeping the same size (for bool-to-char). */
(simplify
(view_convert (convert@0 @1))
- (if ((INTEGRAL_TYPE_P (TREE_TYPE (@0)) || POINTER_TYPE_P (TREE_TYPE (@0)))
- && (INTEGRAL_TYPE_P (TREE_TYPE (@1)) || POINTER_TYPE_P (TREE_TYPE (@1)))
- && TYPE_SIZE (TREE_TYPE (@0)) == TYPE_SIZE (TREE_TYPE (@1))
- && (TYPE_PRECISION (TREE_TYPE (@0)) == TYPE_PRECISION (TREE_TYPE (@1))
- || (TYPE_PRECISION (TREE_TYPE (@0)) > TYPE_PRECISION (TREE_TYPE (@1))
- && TYPE_UNSIGNED (TREE_TYPE (@1)))))
- (view_convert @1)))
+ (with { tree type0 = TREE_TYPE (@0);
+ tree type1 = TREE_TYPE (@1);
+ bool ok = false;
+ if ((INTEGRAL_TYPE_P (type0) || POINTER_TYPE_P (type0))
+ && (INTEGRAL_TYPE_P (type1) || POINTER_TYPE_P (type1))
+ && TYPE_SIZE (type0) == TYPE_SIZE (type1))
+ {
+ if (TYPE_PRECISION (type0) == TYPE_PRECISION (type1))
+ {
+ if (TREE_CODE (type0) != BITINT_TYPE)
+ ok = true;
+ else
+ {
+ /* Avoid optimizing this if type0 is a _BitInt
+ type with padding bits which are supposed to be
+ extended. */
+ struct bitint_info info;
+ targetm.c.bitint_type_info (TYPE_PRECISION (type0),
+ &info);
+ if (!info.extended)
+ ok = true;
+ else
+ ok = (TYPE_PRECISION (type0)
+ == tree_to_uhwi (TYPE_SIZE (type0)));
+ }
+ }
+ else if (TYPE_PRECISION (type0) > TYPE_PRECISION (type1)
+ && TYPE_UNSIGNED (type1))
+ ok = true;
+ } }
+ (if (ok)
+ (view_convert @1))))
/* Simplify a view-converted empty or single-element constructor. */
(simplify
Jakub
