Only traverse reachable blocks in JumpThreading.

Author: cjgillot

compiler/rustc_mir_transform/src/jump_threading.rs

@@ -89,7 +89,7 @@ impl<'tcx> crate::MirPass<'tcx> for JumpThreading {
             opportunities: Vec::new(),
         };
 
-        for bb in body.basic_blocks.indices() {
+        for (bb, _) in traversal::preorder(body) {
             finder.start_from_switch(bb);
         }
 

tests/crashes/131451.rs renamed to tests/ui/mir/unreachable-loop-jump-threading.rs

@@ -1,9 +1,10 @@
-//@ known-bug: #131451
+//@ build-pass
 //@ needs-rustc-debug-assertions
 //@ compile-flags: -Zmir-enable-passes=+GVN -Zmir-enable-passes=+JumpThreading --crate-type=lib
 
 pub fn fun(terminate: bool) {
     while true {}
+    //~^ WARN denote infinite loops with `loop { ... }`
 
     while !terminate {}
 }