[Wasm GC] Signature Pruning (#4545)

This adds a new signature-pruning pass that prunes parameters from
signature types where those parameters are never used in any function
that has that type. This is similar to DeadArgumentElimination but works
on a set of functions, and it can handle indirect calls.

Also move a little code from SignatureRefining into a shared place to
avoid duplication of logic to update signature types.

This pattern happens in j2wasm code, for example if all method functions
for some virtual method just return a constant and do not use the this
pointer. 

1 files changed, 4 insertions, 0 deletions

diff --git a/src/passes/pass.cpp b/src/passes/pass.cpp
index 3ac4485e3..04947ae07 100644
--- a/src/passes/pass.cpp
+++ b/src/passes/pass.cpp
@@ -353,6 +353,9 @@ void PassRegistry::registerPasses() {
   registerPass("set-globals",
                "sets specified globals to specified values",
                createSetGlobalsPass);
+  registerPass("signature-pruning",
+               "remove params from function signature types where possible",
+               createSignaturePruningPass);
   registerPass("signature-refining",
                "apply more specific subtypes to signature types where possible",
                createSignatureRefiningPass);
@@ -549,6 +552,7 @@ void PassRunner::addDefaultGlobalOptimizationPrePasses() {
   if (wasm->features.hasGC() && getTypeSystem() == TypeSystem::Nominal &&
       options.optimizeLevel >= 2) {
     addIfNoDWARFIssues("type-refining");
+    addIfNoDWARFIssues("signature-pruning");
     addIfNoDWARFIssues("signature-refining");
     addIfNoDWARFIssues("global-refining");
     // Global type optimization can remove fields that are not needed, which can