[Wasm GC] Fix inlining + non-nullable locals (#3945)

We don't need to assign a zero value for such locals (and we can't, as no
default value exists for them).

Fixes #3944

Author: kripken

src/passes/Inlining.cpp

@@ -292,9 +292,16 @@ doInlining(Module* module, Function* into, const InliningAction& action) {
   // Zero out the vars (as we may be in a loop, and may depend on their
   // zero-init value
   for (Index i = 0; i < from->vars.size(); i++) {
+    auto type = from->vars[i];
+    if (type.isRef() && !type.isNullable()) {
+      // Non-nullable locals do not need to be zeroed out. They have no zero
+      // value, and by definition should not be used before being written to, so
+      // any value we set here would not be observed anyhow.
+      continue;
+    }
     block->list.push_back(
       builder.makeLocalSet(updater.localMapping[from->getVarIndexBase() + i],
-                           LiteralUtils::makeZero(from->vars[i], *module)));
+                           LiteralUtils::makeZero(type, *module)));
   }
   // Generate and update the inlined contents
   auto* contents = ExpressionManipulator::copy(from->body, *module);

test/lit/passes/inlining-gc.wast

@@ -0,0 +1,45 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py and should not be edited.
+;; RUN: wasm-opt %s --inlining --enable-gc-nn-locals -all -S -o - | filecheck %s
+
+(module
+ ;; CHECK:      (func $caller-nullable
+ ;; CHECK-NEXT:  (local $0 funcref)
+ ;; CHECK-NEXT:  (block $__inlined_func$target-nullable
+ ;; CHECK-NEXT:   (local.set $0
+ ;; CHECK-NEXT:    (ref.null func)
+ ;; CHECK-NEXT:   )
+ ;; CHECK-NEXT:   (nop)
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT: )
+ (func $caller-nullable
+  ;; Call a function with a nullable local. After the inlining there will
+  ;; be a new local in this function for the use of the inlined code, and also
+  ;; we assign the null value to that local in the inlined block (which does
+  ;; not matter much here, but in general if we had a loop that the inlined
+  ;; block was inside of, that would be important to get the right behavior).
+  (call $target-nullable)
+ )
+
+ (func $target-nullable
+  (local $1 (ref null func))
+ )
+
+ ;; CHECK:      (func $caller-non-nullable
+ ;; CHECK-NEXT:  (local $0 (ref func))
+ ;; CHECK-NEXT:  (block $__inlined_func$target-non-nullable
+ ;; CHECK-NEXT:   (nop)
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT: )
+ (func $caller-non-nullable
+  ;; Call a function with a non-nullable local. After the inlining there will
+  ;; be a new local in this function for the use of the inlined code. We do not
+  ;; need to zero it out (such locals cannot be used before being set anyhow, so
+  ;; no zero is needed; and we cannot set a zero anyhow as none exists for the
+  ;; type).
+  (call $target-non-nullable)
+ )
+
+ (func $target-non-nullable
+  (local $1 (ref func))
+ )
+)