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, 2 insertions, 2 deletions

diff --git a/src/binaryen-c.h b/src/binaryen-c.h
index 6f244e533..f2027fd1c 100644
--- a/src/binaryen-c.h
+++ b/src/binaryen-c.h
@@ -806,7 +806,7 @@ typedef void* RelooperRef;
 typedef void* RelooperBlockRef;
 
 // Create a relooper instance
-RelooperRef RelooperCreate(void);
+RelooperRef RelooperCreate(BinaryenModuleRef module);
 
 // Create a basic block that ends with nothing, or with some simple branching
 RelooperBlockRef RelooperAddBlock(RelooperRef relooper, BinaryenExpressionRef code);
@@ -827,7 +827,7 @@ void RelooperAddBranchForSwitch(RelooperBlockRef from, RelooperBlockRef to, Bina
 //   @param labelHelper To render irreducible control flow, we may need a helper variable to
 //                      guide us to the right target label. This value should be an index of
 //                      an i32 local variable that is free for us to use.
-BinaryenExpressionRef RelooperRenderAndDispose(RelooperRef relooper, RelooperBlockRef entry, BinaryenIndex labelHelper, BinaryenModuleRef module);
+BinaryenExpressionRef RelooperRenderAndDispose(RelooperRef relooper, RelooperBlockRef entry, BinaryenIndex labelHelper);
 
 //
 // ========= Other APIs =========