cranelift: rewrite x*-1 to ineg(x) (#6052)

* cranelift: rewrite `x*-1` to `ineg(x)`

* Add commuted test

cranelift/codegen/src/opts/algebraic.isle

@@ -62,6 +62,14 @@
                       _))
       (subsume zero))
 
+;; x*-1 == -1*x == ineg(x).
+(rule (simplify (imul ty x (iconst ty c)))
+      (if-let -1 (i64_sextend_imm64 ty c))
+      (ineg ty x))
+(rule (simplify (imul ty (iconst ty c) x))
+      (if-let -1 (i64_sextend_imm64 ty c))
+      (ineg ty x))
+
 ;; x/1 == x.
 (rule (simplify (sdiv ty
                       x

cranelift/filetests/filetests/egraph/algebraic.clif

@@ -250,6 +250,27 @@ block0(v0: i32):
     ; check: return v2
 }
 
+function %mul_minus_one(i32) -> i32 {
+block0(v0: i32):
+    v1 = iconst.i32 0xffff_ffff ; -1
+    v2 = imul v0, v1
+    return v2
+    ; check: v3 = ineg v0
+    ; check: v4 -> v3
+    ; check: return v3
+}
+
+function %mul_minus_one_commuted(i32) -> i32 {
+block0(v0: i32):
+    v1 = iconst.i32 0xffff_ffff ; -1
+    v2 = imul v1, v0
+    return v2
+    ; check: v3 = ineg v0
+    ; check: v5 -> v3
+    ; check: v6 -> v3
+    ; check: return v3
+}
+
 function %or_and_y_with_not_y_i8(i8, i8) -> i8 {
 block0(v0: i8, v1: i8):
     v2 = band v0, v1