Add a `tuple.drop` text pseudoinstruction (#6170)

We previously overloaded `drop` to mean both normal drops of single values and
also drops of tuple values. That works fine in the legacy text parser since it
can infer parent-child relationships directly from the s-expression structure of
the input, so it knows that a drop should drop an entire tuple if the
tuple-producing instruction is a child of the drop. The new text parser,
however, is much more like the binary parser in that it uses instruction types
to create parent-child instructions. The new parser always assumes that `drop`
is meant to drop just a single value because that's what it does in WebAssembly.

Since we want to continue to let `Drop` IR expressions consume tuples, and since
we will need a way to write tests for that IR pattern that work with the new
parser, introduce a new pseudoinstruction, `tuple.drop`, to represent drops of
tuples. This pseudoinstruction only exists in the text format and it parses to
normal `Drop` expressions. `tuple.drop` takes the arity of its operand as an
immediate, which will let the new parser parse it correctly in the future.

1 files changed, 2 insertions, 2 deletions

diff --git a/test/lit/passes/vacuum_all-features.wast b/test/lit/passes/vacuum_all-features.wast
index f85d21692..9b06624cf 100644
--- a/test/lit/passes/vacuum_all-features.wast
+++ b/test/lit/passes/vacuum_all-features.wast
@@ -1286,14 +1286,14 @@
  ;; CHECK-NEXT:  (nop)
  ;; CHECK-NEXT: )
  (func $1
-  (drop
+  (tuple.drop 2
    (block $block (result funcref i32)
     ;; we can vaccum out all parts of this block: the br_if is not taken, there
     ;; is a nop, and the tuple at the end goes to a dropped block anyhow. this
     ;; test specifically verifies handling of tuples containing non-nullable
     ;; types, for which we try to create a zero in an intermediate step along
     ;; the way.
-    (drop
+    (tuple.drop 2
      (br_if $block
       (tuple.make 2
        (ref.func $1)