Tighten up assertions for basic-gvn test. (#10186)

Assert that the v4 assignment is gone. Assert that nothing appears before the v2 assignment, as that would be a surprise worth hearing about.

Author: erikrose

cranelift/filetests/filetests/egraph/basic-gvn.clif

@@ -19,9 +19,9 @@ block2(v6: i32):
 ;; Check that the `iadd` for `v4` is subsumed by `v2`:
 
 ; check: block0(v0: i32, v1: i32):
-; check:      v2 = iadd v0, v1
+; nextln:      v2 = iadd v0, v1
 ; check:  block1:
-; check:      v5 = iadd.i32 v2, v0
+; nextln:      v5 = iadd.i32 v2, v0
 ; nextln:     return v5
 ; check: block2:
 ; nextln:    return v1

cranelift/isle/isle/README.md

@@ -6,4 +6,4 @@ clif instructions to vcode's `MachInst`s in Cranelift.
 ISLE is a statically-typed term-rewriting language. You define rewriting rules
 that map input terms (clif instructions) into output terms (`MachInst`s). These
 rules get compiled down into Rust source test that uses a tree of `match`
-expressions that is as good or better than what you would have written by hand.
+expressions as good as or better than what you would have written by hand.