fixes #24472; let symbol created by template is reused in nimvm branch (#24473)

fixes #24472

Excluding variables which are initialized in the nimvm branch so that
they won't interfere the other branch

(cherry picked from commit e7f48cdd5c)

compiler/sempass2.nim

@@ -212,6 +212,7 @@ proc varDecl(a: PEffects; n: PNode) {.inline.} =
 proc skipHiddenDeref(n: PNode): PNode {.inline.} =
   result = if n.kind == nkHiddenDeref: n[0] else: n
 
+
 proc initVar(a: PEffects, n: PNode; volatileCheck: bool) =
   let n = skipHiddenDeref(n)
   if n.kind != nkSym: return
@@ -1302,7 +1303,9 @@ proc track(tracked: PEffects, n: PNode) =
       track(tracked, last)
   of nkCaseStmt: trackCase(tracked, n)
   of nkWhen: # This should be a "when nimvm" node.
+    let oldState = tracked.init.len
     track(tracked, n[0][1])
+    tracked.init.setLen(oldState)
     track(tracked, n[1][0])
   of nkIfStmt, nkIfExpr: trackIf(tracked, n)
   of nkBlockStmt, nkBlockExpr: trackBlock(tracked, n[1])

lib/pure/volatile.nim

@@ -19,6 +19,7 @@ proc volatileLoad*[T](src: ptr T): T {.inline, noinit.} =
     when defined(js):
       result = src[]
     else:
+      result = default(T)
       {.emit: [result, " = (*(", typeof(src[]), " volatile*)", src, ");"].}
 
 proc volatileStore*[T](dest: ptr T, val: T) {.inline.} =

tests/init/tlet.nim

@@ -83,3 +83,21 @@ proc foo2 =
   doAssert z == 3
 
 foo2()
+
+# bug #24472
+template bar1314(): bool =
+  let hello = true
+  hello
+
+template foo1314*(val: bool): bool =
+  when nimvm:
+    val
+  else:
+    val
+
+proc test() = # Doesn't fail when top level
+  # Original code is calling `unlikely` which has a `nimvm` branch
+  let s = foo1314(bar1314())
+  doAssert s
+
+test()