Handle const eval failure

Author: simonvandel

compiler/rustc_mir/src/transform/const_goto.rs

@@ -76,11 +76,11 @@ impl<'a, 'tcx> Visitor<'tcx> for ConstGotoOptimizationFinder<'a, 'tcx> {
                                 {
                                     // We now know that the Switch matches on the const place, and it is statementless
                                     // Now find which value in the Switch matches the const value.
-                                    let const_value = _const.literal.eval_bits(
+                                    let const_value = _const.literal.try_eval_bits(
                                         self.tcx,
                                         self.param_env,
                                         switch_ty,
-                                    );
+                                    )?;
                                     let found_value_idx_option = targets
                                         .iter()
                                         .enumerate()

src/test/mir-opt/const_goto_const_eval_fail.f.ConstGoto.diff

@@ -0,0 +1,51 @@
+- // MIR for `f` before ConstGoto
++ // MIR for `f` after ConstGoto
+  
+  fn f() -> u64 {
+      let mut _0: u64;                     // return place in scope 0 at $DIR/const_goto_const_eval_fail.rs:6:44: 6:47
+      let mut _1: bool;                    // in scope 0 at $DIR/const_goto_const_eval_fail.rs:7:11: 12:6
+      let mut _2: i32;                     // in scope 0 at $DIR/const_goto_const_eval_fail.rs:8:15: 8:16
+  
+      bb0: {
+          StorageLive(_1);                 // scope 0 at $DIR/const_goto_const_eval_fail.rs:7:11: 12:6
+          StorageLive(_2);                 // scope 0 at $DIR/const_goto_const_eval_fail.rs:8:15: 8:16
+          _2 = const A;                    // scope 0 at $DIR/const_goto_const_eval_fail.rs:8:15: 8:16
+          switchInt(_2) -> [1_i32: bb2, 2_i32: bb2, 3_i32: bb2, otherwise: bb1]; // scope 0 at $DIR/const_goto_const_eval_fail.rs:9:13: 9:14
+      }
+  
+      bb1: {
+          _1 = const true;                 // scope 0 at $DIR/const_goto_const_eval_fail.rs:10:18: 10:22
+          goto -> bb3;                     // scope 0 at $DIR/const_goto_const_eval_fail.rs:8:9: 11:10
+      }
+  
+      bb2: {
+          _1 = const B;                    // scope 0 at $DIR/const_goto_const_eval_fail.rs:9:26: 9:27
+-         goto -> bb3;                     // scope 0 at $DIR/const_goto_const_eval_fail.rs:8:9: 11:10
++         switchInt(_1) -> [false: bb4, otherwise: bb3]; // scope 0 at $DIR/const_goto_const_eval_fail.rs:13:9: 13:14
+      }
+  
+      bb3: {
+-         switchInt(_1) -> [false: bb5, otherwise: bb4]; // scope 0 at $DIR/const_goto_const_eval_fail.rs:13:9: 13:14
+-     }
+- 
+-     bb4: {
+          _0 = const 2_u64;                // scope 0 at $DIR/const_goto_const_eval_fail.rs:14:17: 14:18
+-         goto -> bb6;                     // scope 0 at $DIR/const_goto_const_eval_fail.rs:7:5: 15:6
++         goto -> bb5;                     // scope 0 at $DIR/const_goto_const_eval_fail.rs:7:5: 15:6
+      }
+  
+-     bb5: {
++     bb4: {
+          _0 = const 1_u64;                // scope 0 at $DIR/const_goto_const_eval_fail.rs:13:18: 13:19
+-         goto -> bb6;                     // scope 0 at $DIR/const_goto_const_eval_fail.rs:7:5: 15:6
++         goto -> bb5;                     // scope 0 at $DIR/const_goto_const_eval_fail.rs:7:5: 15:6
+      }
+  
+-     bb6: {
++     bb5: {
+          StorageDead(_2);                 // scope 0 at $DIR/const_goto_const_eval_fail.rs:16:1: 16:2
+          StorageDead(_1);                 // scope 0 at $DIR/const_goto_const_eval_fail.rs:16:1: 16:2
+          return;                          // scope 0 at $DIR/const_goto_const_eval_fail.rs:16:2: 16:2
+      }
+  }
+  

src/test/mir-opt/const_goto_const_eval_fail.rs

@@ -0,0 +1,16 @@
+#![feature(min_const_generics)]
+#![crate_type = "lib"]
+
+// If const eval fails, then don't crash
+// EMIT_MIR const_goto_const_eval_fail.f.ConstGoto.diff
+pub fn f<const A: i32, const B: bool>() -> u64 {
+    match {
+        match A {
+            1 | 2 | 3 => B,
+            _ => true,
+        }
+    } {
+        false => 1,
+        true => 2,
+    }
+}