Cranelift: More simplification opts for `iadd`/`isub` (#7654)

cranelift/codegen/src/opts/arithmetic.isle

@@ -20,6 +20,17 @@
                       x))
       (ineg ty x))
 
+;; x + -y == -y + x == -(y - x) == x - y
+(rule (simplify (iadd ty x (ineg ty y)))
+      (isub ty x y))
+(rule (simplify (iadd ty (ineg ty y) x))
+      (isub ty x y))
+(rule (simplify (ineg ty (isub ty y x)))
+      (isub ty x y))
+;; x - -y == x + y
+(rule (simplify (isub ty x (ineg ty y)))
+      (iadd ty x y))
+
 ;; ineg(ineg(x)) == x.
 (rule (simplify (ineg ty (ineg ty x))) (subsume x))
 
@@ -55,24 +66,16 @@
       (if-let -1 (i64_sextend_imm64 ty c))
       (ineg ty x))
 
-;; (!x) + 1 == 1 + (!x) == !(x) - (-1) == ineg(x)
+;; (!x) + 1 == ineg(x)
 (rule (simplify (iadd ty (bnot ty x) (iconst ty (u64_from_imm64 1))))
       (ineg ty x))
-(rule (simplify (iadd ty (iconst ty (u64_from_imm64 1)) (bnot ty x)))
-      (ineg ty x))
-(rule (simplify (isub ty (bnot ty x) (iconst ty c)))
-      (if-let -1 (i64_sextend_imm64 ty c))
-      (ineg ty x))
 
-;; !(x - 1) == !(x + (-1)) == !((-1) + x) == ineg(x)
+;; !(x - 1) == !(x + (-1)) == ineg(x)
 (rule (simplify (bnot ty (isub ty x (iconst ty (u64_from_imm64 1)))))
       (ineg ty x))
 (rule (simplify (bnot ty (iadd ty x (iconst ty c))))
       (if-let -1 (i64_sextend_imm64 ty c))
       (ineg ty x))
-(rule (simplify (bnot ty (iadd ty (iconst ty c) x)))
-      (if-let -1 (i64_sextend_imm64 ty c))
-      (ineg ty x))
 
 ;; x/1 == x.
 (rule (simplify (sdiv ty

cranelift/codegen/src/opts/bitops.isle

@@ -1,26 +1,18 @@
 ;; Rewrites for `band`, `bnot`, `bor`, `bxor`
 
-;; x | 0 == 0 | x == x | x == x.
+;; x | 0 == x | x == x.
 (rule (simplify (bor ty
                      x
                      (iconst ty (u64_from_imm64 0))))
       (subsume x))
-(rule (simplify (bor ty
-                     (iconst ty (u64_from_imm64 0))
-                     x))
-      (subsume x))
 (rule (simplify (bor ty x x))
       (subsume x))
 
-;; x ^ 0 == 0 ^ x == x.
+;; x ^ 0 == x.
 (rule (simplify (bxor ty
                      x
                      (iconst ty (u64_from_imm64 0))))
       (subsume x))
-(rule (simplify (bxor ty
-                     (iconst ty (u64_from_imm64 0))
-                     x))
-      (subsume x))
 
 ;; x ^ x == 0.
 (rule (simplify (bxor (fits_in_64 (ty_int ty)) x x))
@@ -34,18 +26,14 @@
 (rule (simplify (bor (fits_in_64 (ty_int ty)) x (bnot ty x))) (subsume (iconst ty (imm64 (ty_mask ty)))))
 (rule (simplify (bor (fits_in_64 (ty_int ty)) (bnot ty x) x)) (subsume (iconst ty (imm64 (ty_mask ty)))))
 
-;; x & -1 == -1 & x == x & x == x.
+;; x & x == x & -1 == x.
 (rule (simplify (band ty x x)) (subsume x))
 (rule (simplify (band ty x (iconst ty k)))
       (if-let -1 (i64_sextend_imm64 ty k))
       (subsume x))
-(rule (simplify (band ty (iconst ty k) x))
-      (if-let -1 (i64_sextend_imm64 ty k))
-      (subsume x))
 
-;; x & 0 == 0 & x == x & not(x) == not(x) & x == 0.
+;; x & 0 == x & not(x) == not(x) & x == 0.
 (rule (simplify (band ty _ zero @ (iconst ty (u64_from_imm64 0)))) (subsume zero))
-(rule (simplify (band ty zero @ (iconst ty (u64_from_imm64 0)) _)) (subsume zero))
 (rule (simplify (band (fits_in_64 (ty_int ty)) x (bnot ty x))) (subsume (iconst ty (imm64 0))))
 (rule (simplify (band (fits_in_64 (ty_int ty)) (bnot ty x) x)) (subsume (iconst ty (imm64 0))))
 

cranelift/codegen/src/opts/cprop.isle

@@ -173,6 +173,17 @@
        (select ty (iconst _ (u64_from_imm64 0)) x y))
       y)
 
+;; Replace subtraction by a "negative" constant with addition.
+;; Notably, this gives `x - (-1) == x + 1`, so other patterns don't have to
+;; match the subtract-negative-one version too.
+;; TODO: it would be nice to do this for `x + (-1) == x - 1` as well, but
+;; that needs work in lowering first to avoid regressing addressing modes.
+
+(rule (simplify (isub ty x (iconst ty k1)))
+      (if-let k2 (i64_sextend_imm64 ty k1))
+      (if-let $true (u64_lt (i64_as_u64 (i64_neg k2)) (i64_as_u64 k2)))
+      (iadd ty x (iconst ty (imm64_masked ty (i64_as_u64 (i64_neg k2))))))
+
 ;; TODO: fadd, fsub, fmul, fdiv, fneg, fabs
 
 ;; A splat of a constant can become a direct `vconst` with the appropriate bit

cranelift/filetests/filetests/egraph/arithmetic.clif

@@ -20,6 +20,42 @@ block0(v0: i32):
     ; check: return v0
 }
 
+function %add_ineg(i32, i32) -> i32 {
+block0(v0: i32, v1: i32):
+    v2 = ineg v1
+    v3 = iadd v0, v2
+    return v3
+    ; check: v4 = isub v0, v1
+    ; check: return v4
+}
+
+function %ineg_add(i32, i32) -> i32 {
+block0(v0: i32, v1: i32):
+    v2 = ineg v0
+    v3 = iadd v2, v1
+    return v3
+    ; check: v4 = isub v1, v0
+    ; check: return v4
+}
+
+function %sub_ineg(i32, i32) -> i32 {
+block0(v0: i32, v1: i32):
+    v2 = ineg v1
+    v3 = isub v0, v2
+    return v3
+    ; check: v4 = iadd v0, v1
+    ; check: return v4
+}
+
+function %sub_then_ineg(i32, i32) -> i32 {
+block0(v0: i32, v1: i32):
+    v2 = isub v0, v1
+    v3 = ineg v2
+    return v3
+    ; check: v4 = isub v1, v0
+    ; check: return v4
+}
+
 function %imul_ineg_cancel(i32, i32) -> i32 {
 block0(v0: i32, v1: i32):
     v2 = ineg v0
@@ -125,8 +161,8 @@ block0(v0: i32):
     return v3
 }
 
-; check: v4 = ineg v0
+; check: v5 = ineg v0
-; check: return v4
+; check: return v5
 
 function %ineg_not_minus_neg_1(i32) -> i32 {
 block0(v0: i32):
@@ -136,8 +172,8 @@ block0(v0: i32):
     return v3
 }
 
-; check: v4 = ineg v0
+; check: v6 = ineg v0
-; check: return v4
+; check: return v6
 
 function %ineg_not_sub_one(i32) -> i32 {
 block0(v0: i32):
@@ -172,7 +208,17 @@ block0(v0: i32):
 ; check: v6 = ineg v0
 ; check: return v6
 
+function %byte_sub_smax_twice(i8) -> i8 {
+block0(v0: i8):
+    v1 = iconst.i8 127
+    v2 = isub v0, v1
+    v3 = isub v2, v1
+    return v3
+}
 
+; check: v6 = iconst.i8 2
+; check: v7 = iadd v0, v6  ; v6 = 2
+; check: return v7
 
 function %double_fneg(f32) -> f32 {
 block0(v1: f32):

cranelift/filetests/filetests/egraph/cprop.clif

@@ -260,3 +260,25 @@ block0:
 
 ; check: v3 = iconst.i32 0xfff6
 ; nextln: return v3
+
+function %sub_u8max(i8) -> i8 {
+block0(v0: i8):
+    v1 = iconst.i8 255
+    v2 = isub v0, v1
+    return v2
+}
+
+; check: v3 = iconst.i8 1
+; nextln: v4 = iadd v0, v3  ; v3 = 1
+; nextln: return v4
+
+function %sub_u32max(i32) -> i32 {
+block0(v0: i32):
+    v1 = iconst.i32 0xFFFF_FFFF
+    v2 = isub v0, v1
+    return v2
+}
+
+; check: v3 = iconst.i32 1
+; nextln: v4 = iadd v0, v3  ; v3 = 1
+; nextln: return v4

cranelift/filetests/filetests/egraph/shifts.clif

@@ -701,8 +701,8 @@ block0(v0: i8):
 }
 
 ; check: v2 = iconst.i8 1
-; check: v21 = rotr v0, v2  ; v2 = 1
+; check: v16 = rotr v0, v2  ; v2 = 1
-; check: return v21
+; check: return v16
 
 function %rotl_rotr_add(i8, i8, i8) -> i8 {
 block0(v0: i8, v1: i8, v2: i8):
@@ -725,8 +725,8 @@ block0(v0: i8):
 }
 
 ; check: v2 = iconst.i8 1
-; check: v21 = rotl v0, v2  ; v2 = 1
+; check: v16 = rotl v0, v2  ; v2 = 1
-; check: return v21
+; check: return v16
 
 function %rotl_rotr_add(i8, i8, i8) -> i8 {
 block0(v0: i8, v1: i8, v2: i8):