Cranelift: Collapse double extends into a single extend (#5772)

cranelift/codegen/src/opts/algebraic.isle

@@ -6,6 +6,12 @@
 ;; than a piece of the input or a new node that we construct; but we
 ;; can freely rewrite e.g. `x+y-y` to `x`.
 
+;; Chained `uextend` and `sextend`.
+(rule (simplify (uextend ty (uextend _intermediate_ty x)))
+      (uextend ty x))
+(rule (simplify (sextend ty (sextend _intermediate_ty x)))
+      (sextend ty x))
+
 ;; x+0 == 0+x == x.
 (rule (simplify (iadd ty
                       x

cranelift/filetests/filetests/egraph/algebraic.clif

@@ -337,3 +337,23 @@ block0(v1: i32):
 
 ; check: v5 = iconst.i8 1
 ; check: return v5
+
+function %double_uextend(i16) -> i64 {
+block0(v1: i16):
+    v2 = uextend.i32 v1
+    v3 = uextend.i64 v2
+    return v3
+}
+
+; check: v4 = uextend.i64 v1
+; check: return v4
+
+function %double_sextend(i16) -> i64 {
+block0(v1: i16):
+    v2 = sextend.i32 v1
+    v3 = sextend.i64 v2
+    return v3
+}
+
+; check: v4 = sextend.i64 v1
+; check: return v4