Flatten control flow pass (#999)

This pass flattens out control flow in order to achieve 2 properties:

 * Control flow structures (block, loop, if) and control flow operations (br, br_if, br_table, return, unreachable) may only be block children, a loop body, or an if-true or if-false. (I.e., they cannot be nested inside an i32.add, a drop, a call, an if-condition, etc.)

 * Disallow block, loop, and if return values, i.e., do not use control flow to pass around values.

As a result, expressions cannot contain control flow, and overall control flow is simpler, more structured, and more "flat".

This should make things like re-relooping wasm code much easier, as they can run after the cfg is flattened

1 files changed, 1 insertions, 0 deletions

diff --git a/src/passes/pass.cpp b/src/passes/pass.cpp
index 51e76cdf7..50c8da46b 100644
--- a/src/passes/pass.cpp
+++ b/src/passes/pass.cpp
@@ -70,6 +70,7 @@ void PassRegistry::registerPasses() {
   registerPass("dce", "removes unreachable code", createDeadCodeEliminationPass);
   registerPass("duplicate-function-elimination", "removes duplicate functions", createDuplicateFunctionEliminationPass);
   registerPass("extract-function", "leaves just one function (useful for debugging)", createExtractFunctionPass);
+  registerPass("flatten-control-flow", "flattens out control flow to be only on blocks, not nested as expressions", createFlattenControlFlowPass);
   registerPass("inlining", "inlines functions (currently only ones with a single use)", createInliningPass);
   registerPass("legalize-js-interface", "legalizes i64 types on the import/export boundary", createLegalizeJSInterfacePass);
   registerPass("local-cse", "common subexpression elimination inside basic blocks", createLocalCSEPass);