Add a liveness verifier.

The liveness verifier will check that the live ranges are consistent
with the function. It runs as part of the register allocation pipeline
when enable_verifier is set.

The initial implementation checks the live ranges, but not the
ISA-specific constraints and affinities.

lib/cretonne/src/context.rs

@@ -81,7 +81,7 @@ impl Context {
     /// Run the register allocator.
     pub fn regalloc(&mut self, isa: &TargetIsa) -> CtonResult {
         self.regalloc
-            .run(isa, &mut self.func, &self.cfg, &self.domtree);
+            .run(isa, &mut self.func, &self.cfg, &self.domtree)?;
         self.verify_if(isa)
     }
 }

lib/cretonne/src/regalloc/context.rs

@@ -11,6 +11,8 @@ use isa::TargetIsa;
 use regalloc::coloring::Coloring;
 use regalloc::live_value_tracker::LiveValueTracker;
 use regalloc::liveness::Liveness;
+use result::CtonResult;
+use verifier::verify_liveness;
 
 /// Persistent memory allocations for register allocation.
 pub struct Context {
@@ -40,7 +42,8 @@ impl Context {
                isa: &TargetIsa,
                func: &mut Function,
                cfg: &ControlFlowGraph,
-               domtree: &DominatorTree) {
+               domtree: &DominatorTree)
+               -> CtonResult {
         // `Liveness` and `Coloring` are self-clearing.
         // Tracker state (dominator live sets) is actually reused between the spilling and coloring
         // phases.
@@ -49,10 +52,16 @@ impl Context {
         // First pass: Liveness analysis.
         self.liveness.compute(isa, func, cfg);
 
+        if isa.flags().enable_verifier() {
+            verify_liveness(isa, func, cfg, &self.liveness)?;
+        }
+
         // TODO: Second pass: Spilling.
 
         // Third pass: Reload and coloring.
         self.coloring
             .run(isa, func, domtree, &mut self.liveness, &mut self.tracker);
+
+        Ok(())
     }
 }

lib/cretonne/src/regalloc/liverange.rs

@@ -174,12 +174,12 @@ pub struct LiveRange {
 /// for contiguous EBBs where all but the last live-in interval covers the whole EBB.
 ///
 #[derive(Copy, Clone)]
-struct Interval {
+pub struct Interval {
     /// Interval starting point.
     ///
     /// Since this interval does not represent the def of the value, it must begin at an EBB header
     /// where the value is live-in.
-    begin: Ebb,
+    pub begin: Ebb,
 
     /// Interval end point.
     ///
@@ -190,7 +190,7 @@ struct Interval {
     /// When this represents multiple contiguous live-in intervals, this is the end point of the
     /// last interval. The other intervals end at the terminator instructions of their respective
     /// EBB.
-    end: Inst,
+    pub end: Inst,
 }
 
 impl Interval {
@@ -368,6 +368,11 @@ impl LiveRange {
             .ok()
             .map(|n| self.liveins[n].end)
     }
+
+    /// Get all the live-in intervals.
+    pub fn liveins(&self) -> &[Interval] {
+        &self.liveins
+    }
 }
 
 /// Allow a `LiveRange` to be stored in a `SparseMap` indexed by values.

lib/cretonne/src/verifier/liveness.rs

@@ -0,0 +1,179 @@
+//! Liveness verifier.
+
+use flowgraph::ControlFlowGraph;
+use ir::{Function, Inst, Value, ProgramOrder, ProgramPoint, ExpandedProgramPoint};
+use ir::entities::AnyEntity;
+use isa::TargetIsa;
+use regalloc::liveness::Liveness;
+use regalloc::liverange::LiveRange;
+use std::cmp::Ordering;
+use verifier::Result;
+
+/// Verify liveness information for `func`.
+///
+/// The provided control flow graph is assumed to be sound.
+///
+/// - All values in the program must have a live range.
+/// - The live range def point must match where the value is defined.
+/// - The live range must reach all uses.
+/// - When a live range is live-in to an EBB, it must be live at all the predecessors.
+/// - The live range affinity must be compatible with encoding constraints.
+///
+/// We don't verify that live ranges are minimal. This would require recomputing live ranges for
+/// all values.
+pub fn verify_liveness(_isa: &TargetIsa,
+                       func: &Function,
+                       cfg: &ControlFlowGraph,
+                       liveness: &Liveness)
+                       -> Result {
+    let verifier = LivenessVerifier {
+        func: func,
+        cfg: cfg,
+        liveness: liveness,
+    };
+    verifier.check_ebbs()?;
+    verifier.check_insts()?;
+    Ok(())
+}
+
+struct LivenessVerifier<'a> {
+    func: &'a Function,
+    cfg: &'a ControlFlowGraph,
+    liveness: &'a Liveness,
+}
+
+impl<'a> LivenessVerifier<'a> {
+    /// Check all EBB arguments.
+    fn check_ebbs(&self) -> Result {
+        for ebb in self.func.layout.ebbs() {
+            for &val in self.func.dfg.ebb_args(ebb) {
+                let lr = match self.liveness.get(val) {
+                    Some(lr) => lr,
+                    None => return err!(ebb, "EBB arg {} has no live range", val),
+                };
+                self.check_lr(ebb.into(), val, lr)?;
+            }
+        }
+        Ok(())
+    }
+
+    /// Check all instructions.
+    fn check_insts(&self) -> Result {
+        for ebb in self.func.layout.ebbs() {
+            for inst in self.func.layout.ebb_insts(ebb) {
+                // Check the defs.
+                for &val in self.func.dfg.inst_results(inst) {
+                    let lr = match self.liveness.get(val) {
+                        Some(lr) => lr,
+                        None => return err!(inst, "{} has no live range", val),
+                    };
+                    self.check_lr(inst.into(), val, lr)?;
+                }
+
+                // Check the uses.
+                for &val in self.func.dfg.inst_args(inst) {
+                    let lr = match self.liveness.get(val) {
+                        Some(lr) => lr,
+                        None => return err!(inst, "{} has no live range", val),
+                    };
+                    if !self.live_at_use(lr, inst) {
+                        return err!(inst, "{} is not live at this use", val);
+                    }
+                }
+            }
+        }
+        Ok(())
+    }
+
+    /// Is `lr` live at the use `inst`?
+    fn live_at_use(&self, lr: &LiveRange, inst: Inst) -> bool {
+        let l = &self.func.layout;
+
+        // Check if `inst` is in the def range, not including the def itself.
+        if l.cmp(lr.def(), inst) == Ordering::Less &&
+           l.cmp(inst, lr.def_local_end()) != Ordering::Greater {
+            return true;
+        }
+
+        // Otherwise see if `inst` is in one of the live-in ranges.
+        match lr.livein_local_end(l.inst_ebb(inst).unwrap(), l) {
+            Some(end) => l.cmp(inst, end) != Ordering::Greater,
+            None => false,
+        }
+    }
+
+    /// Check the integrity of the live range `lr`.
+    fn check_lr(&self, def: ProgramPoint, val: Value, lr: &LiveRange) -> Result {
+        let l = &self.func.layout;
+
+        let loc: AnyEntity = match def.into() {
+            ExpandedProgramPoint::Ebb(e) => e.into(),
+            ExpandedProgramPoint::Inst(i) => i.into(),
+        };
+        if lr.def() != def {
+            return err!(loc, "Wrong live range def ({}) for {}", lr.def(), val);
+        }
+        if lr.is_dead() {
+            if !lr.is_local() {
+                return err!(loc, "Dead live range {} should be local", val);
+            } else {
+                return Ok(());
+            }
+        }
+        let def_ebb = match def.into() {
+            ExpandedProgramPoint::Ebb(e) => e,
+            ExpandedProgramPoint::Inst(i) => l.inst_ebb(i).unwrap(),
+        };
+        match lr.def_local_end().into() {
+            ExpandedProgramPoint::Ebb(e) => {
+                return err!(loc, "Def local range for {} can't end at {}", val, e)
+            }
+            ExpandedProgramPoint::Inst(i) => {
+                if self.func.layout.inst_ebb(i) != Some(def_ebb) {
+                    return err!(loc, "Def local end for {} in wrong ebb", val);
+                }
+            }
+        }
+
+        // Now check the live-in intervals against the CFG.
+        for &livein in lr.liveins() {
+            let mut ebb = livein.begin;
+            if !l.is_ebb_inserted(ebb) {
+                return err!(loc, "{} livein at {} which is not in the layout", val, ebb);
+            }
+            let end_ebb = match l.inst_ebb(livein.end) {
+                Some(e) => e,
+                None => {
+                    return err!(loc,
+                                "{} livein for {} ends at {} which is not in the layout",
+                                val,
+                                ebb,
+                                livein.end)
+                }
+            };
+
+            // Check all the EBBs in the interval independently.
+            loop {
+                // If `val` is live-in at `ebb`, it must be live at all the predecessors.
+                for &(_, pred) in self.cfg.get_predecessors(ebb) {
+                    if !self.live_at_use(lr, pred) {
+                        return err!(pred,
+                                    "{} is live in to {} but not live at predecessor",
+                                    val,
+                                    ebb);
+                    }
+                }
+
+                if ebb == end_ebb {
+                    break;
+                }
+                ebb = match l.next_ebb(ebb) {
+                    Some(e) => e,
+                    None => return err!(loc, "end of {} livein ({}) never reached", val, end_ebb),
+                };
+            }
+        }
+
+        Ok(())
+    }
+}

lib/cretonne/src/verifier/mod.rs

@@ -64,6 +64,27 @@ use std::fmt::{self, Display, Formatter};
 use std::result;
 use std::collections::BTreeSet;
 
+pub use self::liveness::verify_liveness;
+
+// Create an `Err` variant of `Result<X>` from a location and `format!` arguments.
+macro_rules! err {
+    ( $loc:expr, $msg:expr ) => {
+        Err(::verifier::Error {
+            location: $loc.into(),
+            message: String::from($msg),
+        })
+    };
+
+    ( $loc:expr, $fmt:expr, $( $arg:expr ),+ ) => {
+        Err(::verifier::Error {
+            location: $loc.into(),
+            message: format!( $fmt, $( $arg ),+ ),
+        })
+    };
+}
+
+mod liveness;
+
 /// A verifier error.
 #[derive(Debug, PartialEq, Eq)]
 pub struct Error {
@@ -88,23 +109,6 @@ impl std_error::Error for Error {
 /// Verifier result.
 pub type Result = result::Result<(), Error>;
 
-// Create an `Err` variant of `Result<X>` from a location and `format!` arguments.
-macro_rules! err {
-    ( $loc:expr, $msg:expr ) => {
-        Err(Error {
-            location: $loc.into(),
-            message: String::from($msg),
-        })
-    };
-
-    ( $loc:expr, $fmt:expr, $( $arg:expr ),+ ) => {
-        Err(Error {
-            location: $loc.into(),
-            message: format!( $fmt, $( $arg ),+ ),
-        })
-    };
-}
-
 /// Verify `func`.
 pub fn verify_function(func: &Function) -> Result {
     Verifier::new(func).run()

src/utils.rs

@@ -40,7 +40,7 @@ pub fn pretty_verifier_error(func: &ir::Function, err: verifier::Error) -> Strin
         AnyEntity::Inst(inst) => {
             write!(msg, "\n{}: {}\n\n", inst, func.dfg.display_inst(inst)).unwrap()
         }
-        _ => {}
+        _ => msg.push('\n'),
     }
     write_function(&mut msg, func, None).unwrap();
     msg