From: Tomasz Miąsko <tomasz.miasko@gmail.com>
Date: Mon, 3 Aug 2020 00:00:00 +0000 (+0000)
Subject: Fix change detection in CfgSimplifier::collapse_goto_chain
X-Git-Url: https://git.lizzy.rs/?a=commitdiff_plain;h=82651db9b2f6ecb16c773e8afa301c862118bb82;p=rust.git

Fix change detection in CfgSimplifier::collapse_goto_chain

Check that the old target is different from the new collapsed one,
before concluding that anything changed.
---

diff --git a/src/librustc_mir/transform/simplify.rs b/src/librustc_mir/transform/simplify.rs
index 9288d6e16f5..acf8c0181ce 100644
--- a/src/librustc_mir/transform/simplify.rs
+++ b/src/librustc_mir/transform/simplify.rs
@@ -212,6 +212,7 @@ fn collapse_goto_chain(&mut self, start: &mut BasicBlock, changed: &mut bool) {
                 Terminator { kind: TerminatorKind::Goto { ref mut target }, .. } => target,
                 _ => unreachable!(),
             };
+            *changed |= *target != last;
             *target = last;
             debug!("collapsing goto chain from {:?} to {:?}", current, target);
 
@@ -223,7 +224,6 @@ fn collapse_goto_chain(&mut self, start: &mut BasicBlock, changed: &mut bool) {
                 self.pred_count[*target] += 1;
                 self.pred_count[current] -= 1;
             }
-            *changed = true;
             self.basic_blocks[current].terminator = Some(terminator);
         }
     }
diff --git a/src/test/ui/issues/issue-75704.rs b/src/test/ui/issues/issue-75704.rs
new file mode 100644
index 00000000000..aed7ddbcb8c
--- /dev/null
+++ b/src/test/ui/issues/issue-75704.rs
@@ -0,0 +1,7 @@
+// Caused an infinite loop during SimlifyCfg MIR transform previously.
+//
+// build-pass
+
+fn main() {
+    loop { continue; }
+}