Step limit is now terminator limit

Author: oli-obk

src/librustc/mir/interpret/error.rs

@@ -196,7 +196,7 @@ impl<'tcx> Error for EvalError<'tcx> {
             OutOfMemory{..} =>
                 "could not allocate more memory",
             ExecutionTimeLimitReached =>
-                "reached the configured maximum execution time",
+                "the expression was too complex to be evaluated or resulted in an infinite loop",
             StackFrameLimitReached =>
                 "reached the configured maximum number of stack frames",
             OutOfTls =>

src/librustc_mir/interpret/eval_context.rs

@@ -41,7 +41,7 @@ pub struct EvalContext<'a, 'mir, 'tcx: 'a + 'mir, M: Machine<'mir, 'tcx>> {
     /// The maximum number of stack frames allowed
     pub(crate) stack_limit: usize,
 
-    /// The maximum number of operations that may be executed.
+    /// The maximum number of terminators that may be evaluated.
     /// This prevents infinite loops and huge computations from freezing up const eval.
     /// Remove once halting problem is solved.
     pub(crate) steps_remaining: usize,

src/librustc_mir/interpret/step.rs

@@ -19,7 +19,6 @@ impl<'a, 'mir, 'tcx, M: Machine<'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M> {
 
     /// Returns true as long as there are more things to do.
     pub fn step(&mut self) -> EvalResult<'tcx, bool> {
-        self.inc_step_counter_and_check_limit(1)?;
         if self.stack.is_empty() {
             return Ok(false);
         }
@@ -37,6 +36,8 @@ impl<'a, 'mir, 'tcx, M: Machine<'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M> {
             return Ok(true);
         }
 
+        self.inc_step_counter_and_check_limit(1)?;
+
         let terminator = basic_block.terminator();
         assert_eq!(old_frames, self.cur_frame());
         self.terminator(terminator)?;