merge bundles much faster by just concatenating range-lists and unstable-sorting, rather than a merge-sort-like traversal. Rust stdlib sort is very optimized. clang.wasm 9.1s -> 6.8s now.

src/ion/mod.rs

@@ -264,6 +264,16 @@ impl LiveBundle {
         self.spill_weight_and_props & (1 << 29) != 0
     }
 
+    #[inline(always)]
+    fn set_cached_fixed(&mut self) {
+        self.spill_weight_and_props |= 1 << 30;
+    }
+
+    #[inline(always)]
+    fn set_cached_stack(&mut self) {
+        self.spill_weight_and_props |= 1 << 29;
+    }
+
     #[inline(always)]
     fn cached_spill_weight(&self) -> u32 {
         self.spill_weight_and_props & ((1 << 29) - 1)
@@ -2071,6 +2081,11 @@ impl<'a, F: Function> Env<'a, F> {
         }
 
         // Check for a requirements conflict.
+        if self.bundles[from.index()].cached_stack()
+            || self.bundles[from.index()].cached_fixed()
+            || self.bundles[to.index()].cached_stack()
+            || self.bundles[to.index()].cached_fixed()
+        {
             let req = self
                 .compute_requirement(from)
                 .merge(self.compute_requirement(to));
@@ -2078,6 +2093,7 @@ impl<'a, F: Function> Env<'a, F> {
                 log::debug!(" -> conflicting requirements; aborting merge");
                 return false;
             }
+        }
 
         log::debug!(" -> committing to merge");
 
@@ -2085,8 +2101,6 @@ impl<'a, F: Function> Env<'a, F> {
         // them!  We do this with a merge-sort-like scan over both
         // lists, building a new range list and replacing the list on
         // `to` when we're done.
-        let mut idx_from = 0;
-        let mut idx_to = 0;
         if ranges_from.is_empty() {
             // `from` bundle is empty -- trivial merge.
             log::debug!(" -> from bundle{} is empty; trivial merge", from.index());
@@ -2115,52 +2129,47 @@ impl<'a, F: Function> Env<'a, F> {
             }
             self.bundles[to.index()].ranges = list;
 
+            if self.bundles[from.index()].cached_stack() {
+                self.bundles[to.index()].set_cached_stack();
+            }
+            if self.bundles[from.index()].cached_fixed() {
+                self.bundles[to.index()].set_cached_fixed();
+            }
+
             return true;
         }
 
-        // Two non-empty lists of LiveRanges: traverse both simultaneously and
-        // merge ranges into `merged`.
-        let mut merged: LiveRangeList = smallvec![];
         log::debug!(
             "merging: ranges_from = {:?} ranges_to = {:?}",
             ranges_from,
             ranges_to
         );
-        while idx_from < ranges_from.len() || idx_to < ranges_to.len() {
+
-            if idx_from < ranges_from.len() && idx_to < ranges_to.len() {
+        // Two non-empty lists of LiveRanges: concatenate and
-                if ranges_from[idx_from].range.from <= ranges_to[idx_to].range.from {
+        // sort. This is faster than a mergesort-like merge into a new
-                    self.ranges[ranges_from[idx_from].index.index()].bundle = to;
+        // list, empirically.
-                    merged.push(ranges_from[idx_from]);
+        let from_list = std::mem::replace(&mut self.bundles[from.index()].ranges, smallvec![]);
-                    idx_from += 1;
+        for entry in &from_list {
-                } else {
-                    merged.push(ranges_to[idx_to]);
-                    idx_to += 1;
-                }
-            } else if idx_from < ranges_from.len() {
-                for entry in &ranges_from[idx_from..] {
             self.ranges[entry.index.index()].bundle = to;
         }
-                merged.extend_from_slice(&ranges_from[idx_from..]);
+        self.bundles[to.index()]
-                break;
+            .ranges
-            } else {
+            .extend_from_slice(&from_list[..]);
-                assert!(idx_to < ranges_to.len());
+        self.bundles[to.index()]
-                merged.extend_from_slice(&ranges_to[idx_to..]);
+            .ranges
-                break;
+            .sort_unstable_by_key(|entry| entry.range.from);
-            }
-        }
 
-        #[cfg(debug_assertions)]
+        if self.annotations_enabled {
-        {
+            log::debug!("merging: merged = {:?}", self.bundles[to.index()].ranges);
-            log::debug!("merging: merged = {:?}", merged);
             let mut last_range = None;
-            for entry in &merged {
+            for i in 0..self.bundles[to.index()].ranges.len() {
+                let entry = self.bundles[to.index()].ranges[i];
                 if last_range.is_some() {
                     assert!(last_range.unwrap() < entry.range);
                 }
                 last_range = Some(entry.range);
 
                 if self.ranges[entry.index.index()].bundle == from {
-                    if self.annotations_enabled {
                     self.annotate(
                         entry.range.from,
                         format!(
@@ -2172,7 +2181,6 @@ impl<'a, F: Function> Env<'a, F> {
                         ),
                     );
                 }
-                }
 
                 log::debug!(
                     " -> merged result for bundle{}: range{}",
@@ -2182,9 +2190,6 @@ impl<'a, F: Function> Env<'a, F> {
             }
         }
 
-        self.bundles[to.index()].ranges = merged;
-        self.bundles[from.index()].ranges.clear();
-
         if self.bundles[from.index()].spillset != self.bundles[to.index()].spillset {
             let from_vregs = std::mem::replace(
                 &mut self.spillsets[self.bundles[from.index()].spillset.index()].vregs,
@@ -2198,6 +2203,13 @@ impl<'a, F: Function> Env<'a, F> {
             }
         }
 
+        if self.bundles[from.index()].cached_stack() {
+            self.bundles[to.index()].set_cached_stack();
+        }
+        if self.bundles[from.index()].cached_fixed() {
+            self.bundles[to.index()].set_cached_fixed();
+        }
+
         true
     }
 
@@ -2239,6 +2251,28 @@ impl<'a, F: Function> Env<'a, F> {
                 self.ranges[entry.index.index()].bundle = bundle;
             }
 
+            let mut fixed = false;
+            let mut stack = false;
+            for entry in &self.bundles[bundle.index()].ranges {
+                for u in &self.ranges[entry.index.index()].uses {
+                    if let OperandPolicy::FixedReg(_) = u.operand.policy() {
+                        fixed = true;
+                    }
+                    if let OperandPolicy::Stack = u.operand.policy() {
+                        stack = true;
+                    }
+                    if fixed && stack {
+                        break;
+                    }
+                }
+            }
+            if fixed {
+                self.bundles[bundle.index()].set_cached_fixed();
+            }
+            if stack {
+                self.bundles[bundle.index()].set_cached_stack();
+            }
+
             // Create a spillslot for this bundle.
             let ssidx = SpillSetIndex::new(self.spillsets.len());
             let reg = self.vreg_regs[vreg.index()];