Relooper CFG optimizations (#1759)

Previously the relooper would do some optimizations when deciding when to use an if vs a switch, how to group blocks, etc. This PR adds an additional pre-optimization phase with some basic but useful simplify-cfg style passes,

* Skip empty blocks when they have just one exit.
* Merge exiting branches when they are equivalent.
* Canonicalize block contents to make such comparisons more useful.
* Turn a trivial one-target switch into a simple branch.

This can help in noticeable ways when running the rereloop pass, e.g. on LLVM wasm backend output.

Also:

* Binaryen C API changes to the relooper, which now gets a Module for its constructor. It needs it for the optimizations, as it may construct new nodes.
* Many relooper-fuzzer improvements.
* Clean up HashType usage.

1 files changed, 5 insertions, 5 deletions

diff --git a/src/ir/ExpressionAnalyzer.cpp b/src/ir/ExpressionAnalyzer.cpp
index 44abc2f64..f9b981129 100644
--- a/src/ir/ExpressionAnalyzer.cpp
+++ b/src/ir/ExpressionAnalyzer.cpp
@@ -305,14 +305,14 @@ bool ExpressionAnalyzer::flexibleEqual(Expression* left, Expression* right, Expr
 
 
 // hash an expression, ignoring superficial details like specific internal names
-uint32_t ExpressionAnalyzer::hash(Expression* curr) {
-  uint32_t digest = 0;
+HashType ExpressionAnalyzer::hash(Expression* curr) {
+  HashType digest = 0;
 
-  auto hash = [&digest](uint32_t hash) {
+  auto hash = [&digest](HashType hash) {
     digest = rehash(digest, hash);
   };
   auto hash64 = [&digest](uint64_t hash) {
-    digest = rehash(rehash(digest, uint32_t(hash >> 32)), uint32_t(hash));
+    digest = rehash(rehash(digest, HashType(hash >> 32)), HashType(hash));
   };
 
   std::vector<Name> nameStack;
@@ -498,7 +498,7 @@ uint32_t ExpressionAnalyzer::hash(Expression* curr) {
         hash(c->type);
         auto bits = c->value.getBits();
         if (getTypeSize(c->type) == 4) {
-          hash(uint32_t(bits));
+          hash(HashType(bits));
         } else {
           hash64(bits);
         }