fix #29175, invalid lowered IR from repeating code for declared types

src/julia-syntax.scm

@@ -2750,12 +2750,37 @@ f(x) = yt(x)
         ,(delete-duplicates (append (lam:sp lam) capt-sp)))
       ,body)))
 
+;; renumber ssavalues assigned in an expr, allowing it to be repeated
+(define (renumber-assigned-ssavalues e)
+  (let ((vals (expr-find-all (lambda (x) (and (assignment? x) (ssavalue? (cadr x))))
+                             e
+                             cadadr)))
+    (if (null? vals)
+        e
+        (let ((repl (table)))
+          (for-each (lambda (id) (put! repl id (make-ssavalue)))
+                    vals)
+          (let do-replace ((x e))
+            (if (or (atom? x) (quoted? x))
+                x
+                (if (eq? (car x) 'ssavalue)
+                    (or (get repl (cadr x) #f) x)
+                    (cons (car x)
+                          (map do-replace (cdr x))))))))))
+
 (define (convert-for-type-decl rhs t)
   (if (equal? t '(core Any))
       rhs
-      `(call (core typeassert)
-             (call (top convert) ,t ,rhs)
-             ,t)))
+      (let* ((temp (if (or (atom? t) (ssavalue? t) (quoted? t))
+                       #f
+                       (make-ssavalue)))
+             (ty   (or temp t))
+             (ex   `(call (core typeassert)
+                          (call (top convert) ,ty ,rhs)
+                          ,ty)))
+        (if temp
+            `(block (= ,temp ,(renumber-assigned-ssavalues t)) ,ex)
+            ex))))
 
 ;; convert assignment to a closed variable to a setfield! call.
 ;; while we're at it, generate `convert` calls for variables with

test/core.jl

@@ -6714,3 +6714,12 @@ struct T29145{A,B}
     end
 end
 @test_throws TypeError T29145()
+
+# issue #29175
+function f29175(tuple::T) where {T<:Tuple}
+    prefix::Tuple{T.parameters[1:end-1]...} = tuple[1:length(T.parameters)-1]
+    x = prefix
+    prefix = x  # force another conversion to declared type
+    return prefix
+end
+@test f29175((1,2,3)) === (1,2)