master: Revert do-conset-elements to older logic on 3 backends

The branch "master" has been updated in SBCL:
       via  573b76f06944bac4527b76c13cb8081b3762e6e4 (commit)
      from  0aeedbcaf61cf8944848ad57c431caa529b9e5b7 (commit)

- Log -----------------------------------------------------------------
commit 573b76f06944bac4527b76c13cb8081b3762e6e4
Author: Douglas Katzman <[email protected]>
Date:   Fri Jul 17 20:03:21 2026 +0000

    Revert do-conset-elements to older logic on 3 backends
---
 src/compiler/constraint.lisp | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/compiler/constraint.lisp b/src/compiler/constraint.lisp
index 517b0013a..5b8307287 100644
--- a/src/compiler/constraint.lisp
+++ b/src/compiler/constraint.lisp
@@ -514,7 +514,13 @@
              #-sb-xc-host (the simple-vector (sb-kernel:%array-data *constraint-universe*))
              #+sb-xc-host *constraint-universe*))
        (declare (optimize speed))
-       #-sb-xc-host
+       ;; Some backends do not implement either count-leading-zeros or count-trailing-zeros
+       ;; efficiently. For those, iterating over all bits of a simple-bit-vector
+       ;; uses potentially fewer cycles than scanning for just the 1 bits.
+       ;; - Loongarch supports these in the base architecture but our vop is deficient
+       ;; - Sparc added LZCNT no earlier than V9, but not on all V9 implementations
+       ;; - Risc-v only implements something if the Zbb extension is supported
+       #+(and (not sb-xc-host) (not (or sparc loongarch64 riscv)))
        ;; Aligning to word boundaries is valid because MIN and MAX are merely hints about where
        ;; nonzero bits exist.
        (let ((,minword (floor (conset-min ,conset) sb-vm:n-word-bits))
@@ -540,7 +546,7 @@
                                            (* ,index sb-vm:n-word-bits))))))
                       ,@body)))
              finally (return ,result)))
-       #+sb-xc-host
+       #-(and (not sb-xc-host) (not (or sparc loongarch64 riscv)))
        (loop for ,index from (conset-min ,conset) below (conset-max ,conset)
              do (when (plusp (sbit ,conset-vector ,index))
                   (let ((,constraint (aref ,universe ,index)))

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