rustc_mir::transform::simplify - remove nops first

Removing nops can allow more basic blocks to be merged, but merging
basic blocks can't allow for more nops to be removed, so we should
remove nops first.

This doesn't matter *that* much, because normally we run SimplifyCfg
several times, but there's no reason not to do it.

2 files changed, 10 insertions, 16 deletions

diff --git a/src/librustc_mir/transform/simplify.rs b/src/librustc_mir/transform/simplify.rs
index d5b79c0d1c3..a1d56ccd874 100644
--- a/src/librustc_mir/transform/simplify.rs
+++ b/src/librustc_mir/transform/simplify.rs
@@ -105,6 +105,8 @@ impl<'a, 'tcx: 'a> CfgSimplifier<'a, 'tcx> {
     }
 
     pub fn simplify(mut self) {
+        self.strip_nops();
+
         loop {
             let mut changed = false;
 
@@ -141,8 +143,6 @@ impl<'a, 'tcx: 'a> CfgSimplifier<'a, 'tcx> {
 
             if !changed { break }
         }
-
-        self.strip_nops()
     }
 
     // Collapse a goto chain starting from `start`
diff --git a/src/test/mir-opt/basic_assignment.rs b/src/test/mir-opt/basic_assignment.rs
index 6afc344ced8..d3bf7f68785 100644
--- a/src/test/mir-opt/basic_assignment.rs
+++ b/src/test/mir-opt/basic_assignment.rs
@@ -50,10 +50,10 @@ fn main() {
 //         StorageLive(_5);
 //         StorageLive(_6);
 //         _6 = _4;
-//         replace(_5 <- _6) -> [return: bb1, unwind: bb7];
+//         replace(_5 <- _6) -> [return: bb1, unwind: bb5];
 //     }
 //     bb1: {
-//         drop(_6) -> [return: bb8, unwind: bb5];
+//         drop(_6) -> [return: bb6, unwind: bb4];
 //     }
 //     bb2: {
 //         resume;
@@ -62,27 +62,21 @@ fn main() {
 //         drop(_4) -> bb2;
 //     }
 //     bb4: {
-//         goto -> bb3;
+//         drop(_5) -> bb3;
 //     }
 //     bb5: {
-//         drop(_5) -> bb4;
+//         drop(_6) -> bb4;
 //     }
 //     bb6: {
-//         goto -> bb5;
-//     }
-//     bb7: {
-//         drop(_6) -> bb6;
-//     }
-//     bb8: {
 //         StorageDead(_6);
 //         _0 = ();
-//         drop(_5) -> [return: bb9, unwind: bb3];
+//         drop(_5) -> [return: bb7, unwind: bb3];
 //     }
-//     bb9: {
+//     bb7: {
 //         StorageDead(_5);
-//         drop(_4) -> bb10;
+//         drop(_4) -> bb8;
 //     }
-//     bb10: {
+//     bb8: {
 //         StorageDead(_4);
 //         StorageDead(_2);
 //         StorageDead(_1);