Optimization for division by one during constant propagation (#39)

Signed and unsigned divisions by literal 1 are already optimized away during the Selection phase.  This pull request also optimizes those divisions when the 1 divisor is produced by constant propagation.

1 files changed, 16 insertions, 10 deletions

diff --git a/arm/ConstpropOp.vp b/arm/ConstpropOp.vp
index f94606b0..bd08d597 100644
--- a/arm/ConstpropOp.vp
+++ b/arm/ConstpropOp.vp
@@ -160,18 +160,24 @@ Definition make_mulimm (n: int) (r1 r2: reg) :=
     end.
 
 Definition make_divimm (n: int) (r1 r2: reg) :=
-  match Int.is_power2 n with
-  | Some l => if Int.ltu l (Int.repr 31)
-              then (Oshrximm l, r1 :: nil)
-              else (Odiv, r1 :: r2 :: nil)
-  | None   => (Odiv, r1 :: r2 :: nil)
-  end.
+  if Int.eq n Int.one then
+    (Omove, r1 :: nil)
+  else
+    match Int.is_power2 n with
+    | Some l => if Int.ltu l (Int.repr 31)
+                then (Oshrximm l, r1 :: nil)
+                else (Odiv, r1 :: r2 :: nil)
+    | None   => (Odiv, r1 :: r2 :: nil)
+    end.
 
 Definition make_divuimm (n: int) (r1 r2: reg) :=
-  match Int.is_power2 n with
-  | Some l => (Oshift (Slsr (mk_shift_amount l)), r1 :: nil)
-  | None   => (Odivu, r1 :: r2 :: nil)
-  end.
+  if Int.eq n Int.one then
+    (Omove, r1 :: nil)
+  else
+    match Int.is_power2 n with
+    | Some l => (Oshift (Slsr (mk_shift_amount l)), r1 :: nil)
+    | None   => (Odivu, r1 :: r2 :: nil)
+    end.
 
 Definition make_andimm (n: int) (r: reg) (a: aval) :=
   if Int.eq n Int.zero then (Ointconst Int.zero, nil)