From c3f5b71b6af4a8c073aac021a82716f203aa60a4 Mon Sep 17 00:00:00 2001
From: Karl Meakin <karlwfmeakin@gmail.com>
Date: Fri, 17 Mar 2023 19:41:20 +0000
Subject: [PATCH] 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           |  4 ++++
 cranelift/filetests/filetests/egraph/algebraic.clif | 10 ++++++++++
 2 files changed, 14 insertions(+)

diff --git a/cranelift/codegen/src/opts/algebraic.isle b/cranelift/codegen/src/opts/algebraic.isle
index ede83f7c0f..03ed0be235 100644
--- a/cranelift/codegen/src/opts/algebraic.isle
+++ b/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))))
 
diff --git a/cranelift/filetests/filetests/egraph/algebraic.clif b/cranelift/filetests/filetests/egraph/algebraic.clif
index 73c39950de..0687330302 100644
--- a/cranelift/filetests/filetests/egraph/algebraic.clif
+++ b/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