Add EntryRegDiversions to record diversions for each block entry.

cranelift/codegen/src/binemit/mod.rs

@@ -176,7 +176,7 @@ where
 {
     let mut divert = RegDiversions::new();
     for ebb in func.layout.ebbs() {
-        divert.clear();
+        divert.at_ebb(&func.entry_diversions, ebb);
         debug_assert_eq!(func.offsets[ebb], sink.offset());
         for inst in func.layout.ebb_insts(ebb) {
             emit_inst(func, inst, &mut divert, sink, isa);

cranelift/codegen/src/binemit/relaxation.rs

@@ -74,7 +74,7 @@ pub fn relax_branches(
     {
         let mut cur = FuncCursor::new(func);
         while let Some(ebb) = cur.next_ebb() {
-            divert.clear();
+            divert.at_ebb(&cur.func.entry_diversions, ebb);
             cur.func.offsets[ebb] = offset;
             while let Some(inst) = cur.next_inst() {
                 divert.apply(&cur.func.dfg[inst]);
@@ -93,7 +93,8 @@ pub fn relax_branches(
         // Visit all instructions in layout order.
         let mut cur = FuncCursor::new(func);
         while let Some(ebb) = cur.next_ebb() {
-            divert.clear();
+            divert.at_ebb(&cur.func.entry_diversions, ebb);
+
             // Record the offset for `ebb` and make sure we iterate until offsets are stable.
             if cur.func.offsets[ebb] != offset {
                 cur.func.offsets[ebb] = offset;

cranelift/codegen/src/binemit/shrink.rs

@@ -20,7 +20,9 @@ pub fn shrink_instructions(func: &mut Function, isa: &dyn TargetIsa) {
     let mut divert = RegDiversions::new();
 
     for ebb in func.layout.ebbs() {
-        divert.clear();
+        // Load diversions from predecessors.
+        divert.at_ebb(&func.entry_diversions, ebb);
+
         for inst in func.layout.ebb_insts(ebb) {
             let enc = func.encodings[inst];
             if enc.is_legal() {