master: x86-64, struct-by-value: coordinate arglist transforms

The branch "master" has been updated in SBCL:
       via  6a39892471ffe36d723cd07928bff3182bfd8ac5 (commit)
      from  6fff197f3513ef36f05bb919bd1861947434bdf8 (commit)

- Log -----------------------------------------------------------------
commit 6a39892471ffe36d723cd07928bff3182bfd8ac5
Author: Jesse Bouwman <[email protected]>
Date:   Mon Apr 27 14:05:06 2026 -0700

    x86-64, struct-by-value: coordinate arglist transforms
---
 src/compiler/x86-64/c-call.lisp         |  6 ++++++
 tests/alien-struct-by-value.c           | 15 +++++++++++++++
 tests/alien-struct-by-value.impure.lisp | 19 +++++++++++++++++++
 3 files changed, 40 insertions(+)

diff --git a/src/compiler/x86-64/c-call.lisp b/src/compiler/x86-64/c-call.lisp
index 7d20f433d..ef603ab17 100644
--- a/src/compiler/x86-64/c-call.lisp
+++ b/src/compiler/x86-64/c-call.lisp
@@ -520,6 +520,12 @@ Floats are passed in integer registers."
             (and (alien-integer-type-p result-type)
                  (> (sb-alien::alien-integer-type-bits result-type) 64)))
         (collect ((new-args) (lambda-vars) (new-arg-types))
+          ;; When the OUTER struct-return path injected a hidden
+          ;; buffer SAP as the first arg, thread it through.
+          (let ((buf-var (and large-struct-return-p (gensym "BUF"))))
+            (when buf-var
+              (lambda-vars buf-var)
+              (new-args buf-var)))
           (dolist (type arg-types)
             (let ((arg (gensym)))
               (lambda-vars arg)
diff --git a/tests/alien-struct-by-value.c b/tests/alien-struct-by-value.c
index a77cd7136..28f4de700 100644
--- a/tests/alien-struct-by-value.c
+++ b/tests/alien-struct-by-value.c
@@ -427,3 +427,18 @@ struct nest_di nest_di_make(double d, int i) {
   struct nest_di s; s.inner.d = d; s.inner.i = i; return s;
 }
 double nest_di_sum(struct nest_di s) { return s.inner.d + (double)s.inner.i; }
+
+/*
+ * Large struct return + __int128 argument.  Exercise interaction of
+ * hidden sret pointer (injected by the struct-return IR1 transform)
+ * and int128 splitting (rewrites the arg list): these must agree on
+ * whether the buffer arg is present.
+ */
+struct three_u64 { unsigned long long a, b, c; };
+struct three_u64 three_u64_from_u128(__uint128_t x) {
+  struct three_u64 s;
+  s.a = (unsigned long long) x;
+  s.b = (unsigned long long) (x >> 64);
+  s.c = s.a ^ s.b;
+  return s;
+}
diff --git a/tests/alien-struct-by-value.impure.lisp b/tests/alien-struct-by-value.impure.lisp
index c845d43e2..ae685f940 100644
--- a/tests/alien-struct-by-value.impure.lisp
+++ b/tests/alien-struct-by-value.impure.lisp
@@ -786,3 +786,22 @@
     (assert (= (slot (slot s 'inner) 'd) 3.5d0))
     (assert (= (slot (slot s 'inner) 'i) 7))
     (assert (= (nest-di-sum s) 10.5d0))))
+
+;;; Large struct return combined with an __int128 argument: the
+;;; struct-return IR1 transform injects a hidden sret-pointer arg
+;;; ahead of the original args; the int128-splitting transform
+;;; rewrites the arg list.
+#+x86-64
+(with-test (:name :struct-by-value-large-return-with-int128-arg)
+  (define-alien-routine three-u64-from-u128 (struct nil
+                                                    (a (unsigned 64))
+                                                    (b (unsigned 64))
+                                                    (c (unsigned 64)))
+    (x (unsigned 128)))
+  (let* ((low #x0123456789abcdef)
+         (high #xfedcba9876543210)
+         (x (logior low (ash high 64)))
+         (s (three-u64-from-u128 x)))
+    (assert (= (slot s 'a) low))
+    (assert (= (slot s 'b) high))
+    (assert (= (slot s 'c) (logxor low high)))))

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