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

@@ -177,6 +177,7 @@ 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
@@ -1144,7 +1145,12 @@ proc track(tracked: PEffects, n: PNode) =
       let last = lastSon(child)
       track(tracked, last)
   of nkCaseStmt: trackCase(tracked, n)
-  of nkWhen, nkIfStmt, nkIfExpr: trackIf(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])
   of nkWhileStmt:
     # 'while true' loop?

lib/pure/volatile.nim

@@ -19,9 +19,8 @@ template volatileLoad*[T](src: ptr T): T =
     when defined(js):
       src[]
     else:
-      var res: T
-      {.emit: [res, " = (*(", typeof(src[]), " volatile*)", src, ");"].}
-      res
+      result = default(T)
+      {.emit: [result, " = (*(", typeof(src[]), " volatile*)", src, ");"].}
 
 template volatileStore*[T](dest: ptr T, val: T) =
   ## Generates a volatile store into the container `dest` of the value

tests/init/tlet.nim

@@ -53,3 +53,21 @@ proc foo() =
 
 static: foo()
 foo()
+
+# 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()