[Wasm GC] Fix unreachable local.gets of non-nullable locals in CoalesceLocals (#4574)

Normally we just replace unreachable local.gets with a constant (0, or null), but if
the local is non-nullable we can't do that.

Fixes #4573

2 files changed, 26 insertions, 1 deletions

diff --git a/test/lit/passes/coalesce-locals-gc-nn.wast b/test/lit/passes/coalesce-locals-gc-nn.wast
index 21b6d2a33..69e96ac62 100644
--- a/test/lit/passes/coalesce-locals-gc-nn.wast
+++ b/test/lit/passes/coalesce-locals-gc-nn.wast
@@ -81,4 +81,27 @@
    )
   )
  )
+
+ ;; CHECK:      (func $unreachable-get-of-non-nullable
+ ;; CHECK-NEXT:  (local $0 (ref any))
+ ;; CHECK-NEXT:  (unreachable)
+ ;; CHECK-NEXT:  (drop
+ ;; CHECK-NEXT:   (block (result (ref any))
+ ;; CHECK-NEXT:    (unreachable)
+ ;; CHECK-NEXT:   )
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT: )
+ (func $unreachable-get-of-non-nullable
+  ;; One local is unused entirely, the other is used but only in unreachable
+  ;; code. It does not really matter what we do here (coalesce, or not), but we
+  ;; should emit valid IR. Normally we would apply a constant to replace the
+  ;; local.get, however, the types here are non-nullable, so we must do
+  ;; something else.
+  (local $unused (ref any))
+  (local $used-in-unreachable (ref any))
+  (unreachable)
+  (drop
+   (local.get $used-in-unreachable)
+  )
+ )
 )
diff --git a/test/lit/passes/coalesce-locals-gc.wast b/test/lit/passes/coalesce-locals-gc.wast
index 2c0fc3f03..52243ebc8 100644
--- a/test/lit/passes/coalesce-locals-gc.wast
+++ b/test/lit/passes/coalesce-locals-gc.wast
@@ -11,7 +11,9 @@
  ;; CHECK:      (func $test-dead-get-non-nullable (param $0 dataref)
  ;; CHECK-NEXT:  (unreachable)
  ;; CHECK-NEXT:  (drop
- ;; CHECK-NEXT:   (local.get $0)
+ ;; CHECK-NEXT:   (block (result dataref)
+ ;; CHECK-NEXT:    (unreachable)
+ ;; CHECK-NEXT:   )
  ;; CHECK-NEXT:  )
  ;; CHECK-NEXT: )
  (func $test-dead-get-non-nullable (param $func (ref data))