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, 7 insertions, 6 deletions

diff --git a/src/binaryen-c.cpp b/src/binaryen-c.cpp
index 8e9ea8589..b0250a270 100644
--- a/src/binaryen-c.cpp
+++ b/src/binaryen-c.cpp
@@ -2373,12 +2373,13 @@ const char* BinaryenExportGetValue(BinaryenExportRef export_) {
 // ========== CFG / Relooper ==========
 //
 
-RelooperRef RelooperCreate(void) {
+RelooperRef RelooperCreate(BinaryenModuleRef module) {
   if (tracing) {
-    std::cout << "  the_relooper = RelooperCreate();\n";
+    std::cout << "  the_relooper = RelooperCreate(the_module);\n";
   }
 
-  return RelooperRef(new CFG::Relooper());
+  auto* wasm = (Module*)module;
+  return RelooperRef(new CFG::Relooper(wasm));
 }
 
 RelooperBlockRef RelooperAddBlock(RelooperRef relooper, BinaryenExpressionRef code) {
@@ -2440,15 +2441,15 @@ void RelooperAddBranchForSwitch(RelooperBlockRef from, RelooperBlockRef to, Bina
   fromBlock->AddSwitchBranchTo(toBlock, std::move(values), (Expression*)code);
 }
 
-BinaryenExpressionRef RelooperRenderAndDispose(RelooperRef relooper, RelooperBlockRef entry, BinaryenIndex labelHelper, BinaryenModuleRef module) {
+BinaryenExpressionRef RelooperRenderAndDispose(RelooperRef relooper, RelooperBlockRef entry, BinaryenIndex labelHelper) {
   auto* R = (CFG::Relooper*)relooper;
   R->Calculate((CFG::Block*)entry);
-  CFG::RelooperBuilder builder(*(Module*)module, labelHelper);
+  CFG::RelooperBuilder builder(*R->Module, labelHelper);
   auto* ret = R->Render(builder);
 
   if (tracing) {
     auto id = noteExpression(ret);
-    std::cout << "  expressions[" << id << "] = RelooperRenderAndDispose(the_relooper, relooperBlocks[" << relooperBlocks[entry] << "], " << labelHelper << ", the_module);\n";
+    std::cout << "  expressions[" << id << "] = RelooperRenderAndDispose(the_relooper, relooperBlocks[" << relooperBlocks[entry] << "], " << labelHelper << ");\n";
     relooperBlocks.clear();
   }