https://gcc.gnu.org/g:94d2bc6d08caad947a8897a538f2a9b64e16a11a
commit r16-3038-g94d2bc6d08caad947a8897a538f2a9b64e16a11a
Author: Yang Yujie <yangyu...@loongson.cn>
Date: Wed Aug 6 12:03:39 2025 +0200
bitint: Zero-extend the result of a signed->unsigned widening cast
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.
* 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.dg/torture/bitint-83.c: New test.
Diff:
---
gcc/gimple-lower-bitint.cc | 11 ++++++++
gcc/testsuite/gcc.dg/torture/bitint-83.c | 48 ++++++++++++++++++++++++++++++++
2 files changed, 59 insertions(+)
diff --git a/gcc/gimple-lower-bitint.cc b/gcc/gimple-lower-bitint.cc
index 122417371ce8..e7c7fe5f657c 100644
--- a/gcc/gimple-lower-bitint.cc
+++ b/gcc/gimple-lower-bitint.cc
@@ -3181,6 +3181,17 @@ 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);
diff --git a/gcc/testsuite/gcc.dg/torture/bitint-83.c
b/gcc/testsuite/gcc.dg/torture/bitint-83.c
new file mode 100644
index 000000000000..8a9df4431547
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/bitint-83.c
@@ -0,0 +1,48 @@
+/* Derived from a test in gcc.dg/torture/bitint-16.c */
+/* { dg-do run { target bitint } } */
+/* { dg-options "-std=c23 -pedantic-errors" } */
+/* { dg-skip-if "" { ! run_expensive_tests } { "*" } { "-O0" "-O2" } } */
+/* { dg-skip-if "" { ! run_expensive_tests } { "-flto" } { "" } } */
+
+#include "../bitintext.h"
+
+#define BASIC_TESTS \
+ TEST(8) \
+ TEST(16) \
+ TEST(32)
+
+#if __BITINT_MAXWIDTH__ >= 519
+#define ALL_TESTS \
+ BASIC_TESTS \
+ TEST(64) \
+ TEST(128) \
+ TEST(256) \
+ TEST(512)
+#else
+#define ALL_TESTS BASIC_TESTS
+#endif
+
+#define TEST(N) \
+void \
+test##N (unsigned _BitInt(N + 7) *t, _BitInt(N) x) \
+{ \
+ *t = -x; \
+}
+ALL_TESTS
+#undef TEST
+
+volatile int y = 0;
+
+int
+main (void)
+{
+#define TEST(N) \
+ { \
+ unsigned _BitInt(N + 7) t; \
+ _BitInt(N) x = y + N; \
+ test##N (&t, x); \
+ BEXTC (t); \
+ }
+ ALL_TESTS
+#undef TEST
+}
