Implement all Builder::replaceWithIdenticalType() cases as best we can (#3872)

The method had TODOs which it halted on. But we should not halt the
entire program, as this is a best-effort attempt to replace a node with
something simpler of the same type (we call it when we know the value
is not actually used).

1 files changed, 21 insertions, 0 deletions

diff --git a/test/lit/passes/coalesce-locals-gc.wast b/test/lit/passes/coalesce-locals-gc.wast
new file mode 100644
index 000000000..5bad35001
--- /dev/null
+++ b/test/lit/passes/coalesce-locals-gc.wast
@@ -0,0 +1,21 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py and should not be edited.
+;; RUN: wasm-opt %s --coalesce-locals -all -S -o - \
+;; RUN:   | filecheck %s
+
+(module
+ ;; CHECK:      (func $test-dead-get-non-nullable (param $0 dataref)
+ ;; CHECK-NEXT:  (unreachable)
+ ;; CHECK-NEXT:  (drop
+ ;; CHECK-NEXT:   (local.get $0)
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT: )
+ (func $test-dead-get-non-nullable (param $func (ref data))
+  (unreachable)
+  (drop
+   ;; A useless get (that does not read from any set, or from the inputs to the
+   ;; function). Normally we replace such gets with nops as best we can, but in
+   ;; this case the type is non-nullable, so we must leave it alone.
+   (local.get $func)
+  )
+ )
+)