Minor code cleanups (#1617)

* code cleanups in wasm-binary: remove an & param, and standardize whitespace

* add some docs for how the relooper handles blocks with no outgoing branches [ci skip]

Author: kripken

src/binaryen-c.h

@@ -822,7 +822,8 @@ const char* BinaryenExportGetValue(BinaryenExportRef export_);
 // General usage is (1) create a relooper, (2) create blocks, (3) add
 // branches between them, (4) render the output.
 //
-// See Relooper.h for more details
+// For more details, see src/cfg/Relooper.h and
+// https://github.com/WebAssembly/binaryen/wiki/Compiling-to-WebAssembly-with-Binaryen#cfg-api
 
 typedef void* RelooperRef;
 typedef void* RelooperBlockRef;

src/cfg/Relooper.h

@@ -235,6 +235,10 @@ struct Block {
   // Add a branch: if the condition holds we branch (or if null, we branch if all others failed)
   // Note that there can be only one branch from A to B (if you need multiple conditions for the branch,
   // create a more interesting expression in the Condition).
+  // If a Block has no outgoing branches, the contents in Code must contain a terminating
+  // instruction, as the relooper doesn't know whether you want control flow to stop with
+  // an `unreachable` or a `return` or something else (if you forget to do this, control
+  // flow may continue into the block that happens to be emitted right after it).
   void AddBranchTo(Block *Target, wasm::Expression* Condition, wasm::Expression* Code = nullptr);
 
   // Add a switch branch: if the switch condition is one of these values, we branch (or if the list is empty, we are the default)

src/wasm-binary.h

@@ -750,7 +750,7 @@ class WasmBinaryWriter : public Visitor<WasmBinaryWriter, void> {
   // AST writing via visitors
   int depth = 0; // only for debugging
 
-  void recurse(Expression*& curr);
+  void recurse(Expression* curr);
   std::vector<Name> breakStack;
   Function::DebugLocation lastDebugLocation;
   size_t lastBytecodeOffset;