craneleft: cancel ineg when args to imul (#6053)

* craneleft: cancel `ineg`/`iabs` when args to `imul`

* Remove unsound `iabs(x) * iabs(y) == x*y` rewrite

cranelift/codegen/src/opts/algebraic.isle

@@ -35,6 +35,10 @@
 ;; ineg(ineg(x)) == x.
 (rule (simplify (ineg ty (ineg ty x))) (subsume x))
 
+;; ineg(x) * ineg(y) == x*y.
+(rule (simplify (imul ty (ineg ty x) (ineg ty y)))
+      (subsume (imul ty x y)))
+
 ;; x-x == 0.
 (rule (simplify (isub (fits_in_64 (ty_int ty)) x x)) (subsume (iconst ty (imm64 0))))
 

cranelift/filetests/filetests/egraph/algebraic.clif

@@ -232,6 +232,16 @@ block0(v0: i32):
     ; check: return v0
 }
 
+function %imul_ineg_cancel(i32, i32) -> i32 {
+block0(v0: i32, v1: i32):
+    v2 = ineg v0
+    v3 = ineg v1
+    v4 = imul v2, v3
+    return v4
+    ; check: v5 = imul v0, v1
+    ; check: return v5
+}
+
 function %isub_self(i32) -> i32 {
 block0(v0: i32):
     v1 = isub v0, v0