Add C/JS APIs to copy expressions (#2840)

This API enables use cases where we want to keep the original expression, yet utilize passes like `vacuum` or `precompute` to evaluate it without implicitly modifying the original.

C-API: **BinaryenExpressionCopy**(expr, module)
JS-API: **Module#copyExpression**(expr)

1 files changed, 31 insertions, 0 deletions

diff --git a/test/binaryen.js/copy-expression.js b/test/binaryen.js/copy-expression.js
new file mode 100644
index 000000000..261c028fa
--- /dev/null
+++ b/test/binaryen.js/copy-expression.js
@@ -0,0 +1,31 @@
+var module = new binaryen.Module();
+
+// Create an expression and copy it
+var original = module.block(null, [
+  module.if(
+    module.local.get(0, binaryen.i32),
+    module.i32.const(1),
+    module.i32.const(2)
+  )
+], binaryen.i32);
+var copy = module.copyExpression(original);
+
+// Check that the expression incl. sub-expressions are copies
+assert(original !== copy);
+
+var originalInfo = binaryen.getExpressionInfo(original);
+assert(originalInfo.children.length === 1);
+
+var copyInfo = binaryen.getExpressionInfo(copy);
+assert(originalInfo.children.length === copyInfo.children.length);
+assert(originalInfo.children[0] !== copyInfo.children[0]);
+
+var originalIfInfo = binaryen.getExpressionInfo(originalInfo.children[0]);
+var copyIfInfo = binaryen.getExpressionInfo(copyInfo.children[0]);
+
+assert(originalIfInfo.condition !== copyIfInfo.condition);
+assert(originalIfInfo.ifTrue !== copyIfInfo.ifTrue);
+assert(originalIfInfo.ifFalse !== copyIfInfo.ifFalse);
+
+// Check that both are otherwise identical
+assert(binaryen.emitText(original) === binaryen.emitText(copy));