fuzzbug fixes

src/backend/schedule.rs

@@ -91,6 +91,9 @@ impl Schedule {
                         log::trace!("v{} waiting on {:?}", value.index(), operands);
                         ctx.remaining_inputs.insert(value, operands.len());
                         for &input in operands {
+                            if input == Value::undef() {
+                                continue;
+                            }
                             let input = f.resolve_alias(input);
                             ctx.waiting_on_value
                                 .entry(input)

src/backend/use_count.rs

@@ -2,7 +2,7 @@
 
 use std::collections::VecDeque;
 
-use crate::{Value, FunctionBody, ValueDef};
+use crate::{FunctionBody, Value, ValueDef};
 use fxhash::FxHashSet;
 
 #[derive(Clone, Debug)]
@@ -23,17 +23,21 @@ impl UseCountAnalysis {
         let mut workqueue_set = FxHashSet::default();
         for block in 0..f.blocks.len() {
             for &value in &f.blocks[block].insts {
+                if value != Value::undef() {
                     let value = f.resolve_alias(value);
                     if workqueue_set.insert(value) {
                         workqueue.push_back(value);
                     }
                     counts.toplevel.insert(value);
                 }
+            }
             f.blocks[block].terminator.visit_uses(|value| {
+                if value != Value::undef() {
                     let value = f.resolve_alias(value);
                     if workqueue_set.insert(value) {
                         workqueue.push_back(value);
                     }
+                }
             });
 
             while let Some(value) = workqueue.pop_front() {
@@ -43,6 +47,9 @@ impl UseCountAnalysis {
                     &ValueDef::Alias(..) | &ValueDef::Arg(..) | &ValueDef::BlockParam(..) => {}
                     &ValueDef::Operator(_op, ref args) => {
                         for &arg in args {
+                            if arg == Value::undef() {
+                                continue;
+                            }
                             let arg = f.resolve_alias(arg);
                             if counts.use_count[arg.index()] == 0 {
                                 if workqueue_set.insert(arg) {
@@ -52,6 +59,9 @@ impl UseCountAnalysis {
                         }
                     }
                     &ValueDef::PickOutput(value, _) => {
+                        if value == Value::undef() {
+                            continue;
+                        }
                         let value = f.resolve_alias(value);
                         if counts.use_count[value.index()] == 0 {
                             if workqueue_set.insert(value) {

src/ir.rs

@@ -106,6 +106,7 @@ impl FunctionBody {
     }
 
     pub fn resolve_alias(&self, value: Value) -> Value {
+        assert_ne!(value, Value::undef());
         let mut result = value;
         loop {
             if let &ValueDef::Alias(to) = &self.values[result.index()] {