Split critical edge targeting the start block

Author: tmiasko

compiler/rustc_mir/src/transform/add_call_guards.rs

@@ -38,7 +38,9 @@ impl<'tcx> MirPass<'tcx> for AddCallGuards {
 
 impl AddCallGuards {
     pub fn add_call_guards(&self, body: &mut Body<'_>) {
-        let pred_count: IndexVec<_, _> = body.predecessors().iter().map(|ps| ps.len()).collect();
+        let mut pred_count: IndexVec<_, _> =
+            body.predecessors().iter().map(|ps| ps.len()).collect();
+        pred_count[START_BLOCK] += 1;
 
         // We need a place to store the new blocks generated
         let mut new_blocks = Vec::new();

src/test/ui/codegen/issue-88043-bb-does-not-have-terminator.rs

@@ -0,0 +1,35 @@
+// build-pass
+// compile-flags: -Copt-level=0
+
+// Regression test for #88043: LLVM crash when the RemoveZsts mir-opt pass is enabled.
+// We should not see the error:
+// `Basic Block in function '_ZN4main10take_until17h0067b8a660429bc9E' does not have terminator!`
+
+fn bump() -> Option<usize> {
+    unreachable!()
+}
+
+fn take_until(terminate: impl Fn() -> bool) {
+    loop {
+        if terminate() {
+            return;
+        } else {
+            bump();
+        }
+    }
+}
+
+// CHECK-LABEL: @main
+fn main() {
+    take_until(|| true);
+    f(None);
+}
+
+fn f(_a: Option<String>) -> Option<u32> {
+    loop {
+        g();
+        ()
+    }
+}
+
+fn g() -> Option<u32> { None }