Coarsen trycatch regions for contiguous blocks with same rescue.

Fixes #3777. Previously, every basic block with an associated rescue block would get its own trycatch range emitted into JVM bytecode. This may not be an issue on all JVMs, but some may have trouble optimizing code across all those trycatch boundaries. Others may do this coarsening for us, but we're still bloating up the size of the emitted bytecode. Either way, this fix combines contiguous blocks that have the same rescue into a single JVM trycatch.
jruby · Apr 5, 2016 · ff882fc · ff882fc
1 parent e6a5867
commit ff882fc
Showing 1 changed file with 54 additions and 11 deletions.
diff --git a/core/src/main/java/org/jruby/ir/targets/JVMVisitor.java b/core/src/main/java/org/jruby/ir/targets/JVMVisitor.java
@@ -166,23 +166,65 @@ public void emitScope(IRScope scope, String name, Signature signature, boolean s
 
         int numberOfBasicBlocks = bbs.length;
         int ipc = 0; // synthetic, used for debug traces that show which instr failed
+
+        Label currentRescue = null;
+        Label currentRegionStart = null;
+        Label currentBlockStart = null;
+        Map<Label, org.objectweb.asm.Label> rescueEndForStart = new HashMap<>();
+        Map<Label, org.objectweb.asm.Label> syntheticEndForStart = new HashMap<>();
+
         for (int i = 0; i < numberOfBasicBlocks; i++) {
             BasicBlock bb = bbs[i];
-            org.objectweb.asm.Label start = jvm.methodData().getLabel(bb.getLabel());
-            Label rescueLabel = exceptionTable.get(bb);
-            org.objectweb.asm.Label end = null;
+            currentBlockStart = bb.getLabel();
 
-            m.mark(start);
+            Label rescueLabel = exceptionTable.get(bb);
 
-            boolean newEnd = false;
             if (rescueLabel != null) {
-                if (i+1 < numberOfBasicBlocks) {
-                    end = jvm.methodData().getLabel(bbs[i+1].getLabel());
+                if (currentRescue != null) {
+                    if (rescueLabel == currentRescue) {
+                        // continue, inside active rescue region
+                        continue;
+                    } else {
+                        // end of active region and start of new one
+                        rescueEndForStart.put(currentRegionStart, jvm.methodData().getLabel(bb.getLabel()));
+                        currentRescue = rescueLabel;
+                        currentRegionStart = bb.getLabel();
+                    }
                 } else {
-                    newEnd = true;
-                    end = new org.objectweb.asm.Label();
+                    currentRescue = rescueLabel;
+                    currentRegionStart = bb.getLabel();
                 }
+            } else {
+                if (currentRescue == null) {
+                    // continue, no new or active region
+                    continue;
+                } else {
+                    // end of active region, no new region
+                    rescueEndForStart.put(currentRegionStart, jvm.methodData().getLabel(bb.getLabel()));
+                    currentRescue = null;
+                    currentRegionStart = null;
+                }
+            }
+        }
+
+        // handle unclosed final region
+        if (currentRegionStart != null) {
+            org.objectweb.asm.Label syntheticEnd = new org.objectweb.asm.Label();
+            rescueEndForStart.put(currentRegionStart, syntheticEnd);
+            syntheticEndForStart.put(currentBlockStart, syntheticEnd);
+        }
+
+        for (int i = 0; i < numberOfBasicBlocks; i++) {
+            BasicBlock bb = bbs[i];
+            org.objectweb.asm.Label start = jvm.methodData().getLabel(bb.getLabel());
+            Label rescueLabel = exceptionTable.get(bb);
+
+            m.mark(start);
 
+            // if this is the start of a rescued region, emit trycatch
+            org.objectweb.asm.Label end;
+            if (rescueLabel != null && (end = rescueEndForStart.get(bb.getLabel())) != null) {
+                // first entry into a rescue region, do the try/catch
                 org.objectweb.asm.Label rescue = jvm.methodData().getLabel(rescueLabel);
                 jvmAdapter().trycatch(start, end, rescue, p(Throwable.class));
             }
@@ -201,8 +243,9 @@ public void emitScope(IRScope scope, String name, Signature signature, boolean s
                 visit(instr);
             }
 
-            if (newEnd) {
-                m.mark(end);
+            org.objectweb.asm.Label syntheticEnd = syntheticEndForStart.get(bb.getLabel());
+            if (syntheticEnd != null) {
+                m.mark(syntheticEnd);
             }
         }