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

Author: dcodeIO

src/binaryen-c.cpp

@@ -1319,6 +1319,11 @@ void BinaryenExpressionPrint(BinaryenExpressionRef expr) {
   std::cout << '\n';
 }
 
+BinaryenExpressionRef BinaryenExpressionCopy(BinaryenExpressionRef expr,
+                                             BinaryenModuleRef module) {
+  return ExpressionManipulator::copy(expr, *(Module*)module);
+}
+
 // Specific expression utility
 
 // Block

src/binaryen-c.h

@@ -848,6 +848,8 @@ BINARYEN_API BinaryenExpressionId
 BinaryenExpressionGetId(BinaryenExpressionRef expr);
 BINARYEN_API BinaryenType BinaryenExpressionGetType(BinaryenExpressionRef expr);
 BINARYEN_API void BinaryenExpressionPrint(BinaryenExpressionRef expr);
+BINARYEN_API BinaryenExpressionRef
+BinaryenExpressionCopy(BinaryenExpressionRef expr, BinaryenModuleRef module);
 
 BINARYEN_API const char* BinaryenBlockGetName(BinaryenExpressionRef expr);
 BINARYEN_API BinaryenIndex

src/js/binaryen.js-post.js

@@ -2407,6 +2407,9 @@ function wrapModule(module, self) {
   self['setDebugLocation'] = function(func, expr, fileIndex, lineNumber, columnNumber) {
     return Module['_BinaryenFunctionSetDebugLocation'](func, expr, fileIndex, lineNumber, columnNumber);
   };
+  self['copyExpression'] = function(expr) {
+    return Module['_BinaryenExpressionCopy'](expr, module);
+  };
 
   return self;
 }

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));