[Wasm GC] Fix RSE on non-nullable locals (#3943)

RedundantSetElimination checks if a local already has the default
value when we assign the default to it. For a non-nullable local, however,
there is no initial value - it cannot be used before it is assigned to. So
we just need to skip such locals, and not assume they contain a default
value we can compare against (we would assert on trying to create a
"zero" for such a non-nullable type).

Fixes #3942

1 files changed, 15 insertions, 0 deletions

diff --git a/test/lit/passes/rse-gc.wast b/test/lit/passes/rse-gc.wast
new file mode 100644
index 000000000..7bea92260
--- /dev/null
+++ b/test/lit/passes/rse-gc.wast
@@ -0,0 +1,15 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py and should not be edited.
+;; RUN: wasm-opt %s --rse --enable-gc-nn-locals -all -S -o - | filecheck %s
+
+(module
+ ;; CHECK:      (func $10
+ ;; CHECK-NEXT:  (local $1 (ref func))
+ ;; CHECK-NEXT:  (nop)
+ ;; CHECK-NEXT: )
+ (func $10
+  ;; A non-nullable local. The pass should ignore it (as we cannot optimize
+  ;; anything here anyhow: the code must assign to the local before reading from
+  ;; it, so no sets can be redundant in that sense).
+  (local $1 (ref func))
+ )
+)