br_table optimizations (#1502)

Inspired by #1501

 * remove unneeded appearances of the default switch target (at the front or back of the list of targets)
 * optimize a switch with 0, 1 or 2 targets into an if or if-chain
 * optimize a br_if br pair when they have the same target

Makes e.g. fastcomp libc++ 2% smaller. Noticeable improvements on other things like box2d etc.

1 files changed, 5 insertions, 0 deletions

diff --git a/src/mixed_arena.h b/src/mixed_arena.h
index 9354527ec..a1c51b5eb 100644
--- a/src/mixed_arena.h
+++ b/src/mixed_arena.h
@@ -208,6 +208,11 @@ public:
     usedElements++;
   }
 
+  T& front() const {
+    assert(usedElements > 0);
+    return data[0];
+  }
+
   void erase(Iterator start_it, Iterator end_it) {
     assert(start_it.parent == end_it.parent && start_it.parent == this);
     assert(start_it.index <= end_it.index && end_it.index <= usedElements);