A widening cast from a signed _BitInt operand to an unsigned _BitInt
type involves filling the extra limb(s) with sign extension.
On a target that wants _BitInts extended in memory, if this unsigned
type has a partial limb, the unused part of it should be zeroed.
e.g. Assuming limb_mode == E_DImode, at the end of
void
test (unsigned _BitInt(519) *t, _BitInt(512) x)
{
*t = -x;
}
the most significant limb of *t should be masked with 0x7f.
This patch also fixes gcc.dg/torture/bitint-16.c, which aborts at -O2
when the extension on load is optimized away.
gcc/ChangeLog:
* gimple-lower-bitint.cc (bitint_large_huge::lower_mergeable_stmt):
zero-extend the partial limb of any unsigned _BitInt LHS assigned
with a widening sign-extension.
---
gcc/gimple-lower-bitint.cc | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/gcc/gimple-lower-bitint.cc b/gcc/gimple-lower-bitint.cc
index 631a7844790..d80191c6761 100644
--- a/gcc/gimple-lower-bitint.cc
+++ b/gcc/gimple-lower-bitint.cc
@@ -3161,6 +3161,14 @@ bitint_large_huge::lower_mergeable_stmt (gimple *stmt,
tree_code &cmp_code,
{
tree l = limb_access (nlhs ? NULL_TREE : lhs_type,
nlhs ? nlhs : lhs, idx, true);
+
+ if (bitint_extended && sext && TYPE_UNSIGNED (lhs_type)
+ && tree_fits_uhwi_p (idx) && !nlhs)
+ {
+ rhs1 = add_cast (limb_access_type (lhs_type, idx), rhs1);
+ rhs1 = add_cast (TREE_TYPE (l), rhs1);
+ }
+
g = gimple_build_assign (l, rhs1);
}
insert_before (g);
--
2.46.0
