Speculate in simplify-locals that it is worth turning an if into

an if-else.

If an if sets a local,

  (if
    (..condition..)
    (set_local $x (..value..))
  )

we can turn it into

  (set_local $x
    (if
      (..condition..)
      (..value..)
      (get_local $x)
    )
  )

This increases code size and adds a branch in the if, but allows
the set to be optimized into a tee or optimized out entirely. In
the worst case, other optimizations can break up an if with a copy
in one of its arms later.

Includes a determinism fix for EquivalentSets, which this patch
triggered.

1 files changed, 35 insertions, 39 deletions

diff --git a/test/unit.fromasm.imprecise b/test/unit.fromasm.imprecise
index b5da4cfe4..a56482591 100644
--- a/test/unit.fromasm.imprecise
+++ b/test/unit.fromasm.imprecise
@@ -233,20 +233,20 @@
  )
  (func $smallCompare (; 18 ;) (; has Stack IR ;) (param $0 i32) (param $1 i32) (result i32)
   (if
-   (i32.lt_s
-    (get_local $0)
-    (get_local $1)
-   )
-   (set_local $0
-    (i32.add
-     (get_local $0)
-     (i32.const 1)
-    )
-   )
-  )
-  (if
    (i32.lt_u
-    (get_local $0)
+    (tee_local $0
+     (select
+      (i32.add
+       (get_local $0)
+       (i32.const 1)
+      )
+      (get_local $0)
+      (i32.lt_s
+       (get_local $0)
+       (get_local $1)
+      )
+     )
+    )
     (get_local $1)
    )
    (set_local $0
@@ -426,24 +426,20 @@
  (func $zeroInit (; 25 ;) (; has Stack IR ;) (param $0 i32)
   (local $1 i32)
   (if
-   (call $lb
-    (i32.const 0)
-   )
-   (if
-    (call $lb
-     (i32.const 1)
-    )
-    (set_local $1
+   (i32.eq
+    (if (result i32)
+     (call $lb
+      (i32.const 0)
+     )
+     (if (result i32)
+      (call $lb
+       (i32.const 1)
+      )
+      (i32.const 3)
+      (get_local $1)
+     )
      (i32.const 3)
     )
-   )
-   (set_local $1
-    (i32.const 3)
-   )
-  )
-  (if
-   (i32.eq
-    (get_local $1)
     (i32.const 3)
    )
    (drop
@@ -999,16 +995,16 @@
   )
   (if
    (i32.eq
-    (get_local $0)
-    (i32.const 300)
-   )
-   (set_local $1
-    (i32.const 2)
-   )
-  )
-  (if
-   (i32.eq
-    (get_local $1)
+    (tee_local $1
+     (select
+      (i32.const 2)
+      (get_local $1)
+      (i32.eq
+       (get_local $0)
+       (i32.const 300)
+      )
+     )
+    )
     (i32.const 2)
    )
    (call $relooperJumpThreading_irreducible