Optimize equivalent locals (#1540)

If locals are known to contain the same value, we can

*    Pick which local to use for a get_local of any of them. Makes sense to prefer the most common, to increase the chance of one dropping to zero uses.
*    Remove copies between a local and one that we know contains the same value.

This is a consistent win, small though, around 0.1-0.2%.

1 files changed, 98 insertions, 0 deletions

diff --git a/test/passes/simplify-locals.wast b/test/passes/simplify-locals.wast
index 3d82fe0a4..d8d5ff7a6 100644
--- a/test/passes/simplify-locals.wast
+++ b/test/passes/simplify-locals.wast
@@ -1129,4 +1129,102 @@
    )
    (i32.const 0)
   )
+
+  (func $pick
+   (local $x i32)
+   (local $y i32)
+   (set_local $x (get_local $y))
+   (if (i32.const 1)
+    (set_local $x (i32.const 1))
+   )
+   (set_local $x (get_local $y))
+   (set_local $x (get_local $y))
+  )
+  (func $pick-2
+   (local $x i32)
+   (local $y i32)
+   (set_local $y (get_local $x))
+   (if (i32.const 1)
+    (set_local $y (i32.const 1))
+   )
+   (set_local $y (get_local $x))
+   (set_local $y (get_local $x))
+  )
+  (func $many
+   (local $x i32)
+   (local $y i32)
+   (local $z i32)
+   (local $w i32)
+   (set_local $y (get_local $x))
+   (set_local $z (get_local $y))
+   (set_local $w (get_local $z))
+   (set_local $x (get_local $z))
+   (if (i32.const 1)
+    (set_local $y (i32.const 1))
+   )
+   (set_local $x (get_local $z))
+   (if (i32.const 1)
+    (set_local $y (i32.const 1))
+   )
+   (set_local $y (get_local $x))
+   (set_local $z (get_local $y))
+   (set_local $w (get_local $z))
+   (set_local $z (i32.const 2))
+   (set_local $x (get_local $z))
+   (if (i32.const 1)
+    (set_local $y (i32.const 1))
+   )
+   (set_local $y (get_local $x))
+   (set_local $z (get_local $y))
+   (set_local $w (get_local $z))
+   (set_local $z (i32.const 2))
+   (set_local $x (get_local $w))
+  )
+  (func $loop-copies (param $x i32) (param $y i32)
+   (loop $loop
+    (set_local $x (get_local $y))
+    (set_local $y (get_local $x))
+    (br_if $loop (get_local $x))
+   )
+  )
+  (func $proper-type (result f64)
+   (local $var$0 i32)
+   (local $var$2 f64)
+   (set_local $var$0
+    (select
+     (i32.const 0)
+     (i32.const 1)
+     (get_local $var$0)
+    )
+   )
+   (tee_local $var$2
+    (get_local $var$2)
+   )
+  )
+  (func $multi-pass-get-equivs-right (param $var$0 i32) (param $var$1 i32) (result f64)
+   (local $var$2 i32)
+   (set_local $var$2
+    (get_local $var$0)
+   )
+   (i32.store
+    (get_local $var$2)
+    (i32.const 1)
+   )
+   (f64.promote/f32
+    (f32.load
+     (get_local $var$2)
+    )
+   )
+  )
+  (func $if-value-structure-equivalent (param $x i32) (result i32)
+    (local $y i32)
+    (if (i32.const 1)
+      (set_local $x (i32.const 2))
+      (block
+        (set_local $y (get_local $x))
+        (set_local $x (get_local $y))
+      )
+    )
+    (get_local $x)
+  )
 )