Backport some minor speedups

1 files changed, 32 insertions, 0 deletions

diff --git a/chapter20/src/test/java/com/seaofnodes/simple/SchedulingScratchTest.java b/chapter20/src/test/java/com/seaofnodes/simple/SchedulingScratchTest.java
new file mode 100644
index 00000000..319c94b0
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/SchedulingScratchTest.java
@@ -0,0 +1,32 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.codegen.CodeGen;
+import org.junit.Test;
+import static org.junit.Assert.assertEquals;
+
+public class SchedulingScratchTest {
+    @Test public void testScratchAcrossCompilations() {
+        String src = """
+            int[] !xs = new int[2];
+            xs[0] = arg;
+            int sum = 0;
+            int i = 0;
+            while( i<5 ) {
+                int old = xs[arg&1];
+                xs[0] = i;
+                sum = sum + old;
+                i = i + 1;
+            }
+            return sum;
+            """;
+        // Each fresh compilation reuses node IDs and the scheduler's scratch.
+        for( int round=0; round<3; round++ ) {
+            CodeGen code = new CodeGen(src).driver(CodeGen.Phase.TypeCheck);
+            // A small graph after many earlier node allocations.
+            if( round==0 ) code._uid += 100_000;
+            assertEquals("6",Eval2.eval(code,0));
+            assertEquals("0",Eval2.eval(code,1));
+            assertEquals("8",Eval2.eval(code,2));
+        }
+    }
+}