Improve getFallthrough (#1643)

That method looks through tee_locals and other operations that receive a value and let it flow through them, like a block's final value, etc. It just handled a few such operations, with this PR all of them should be handled.

Also refactor it out of the OptimizeInstructions pass as I think it may be useful for propagating returned constants.

1 files changed, 47 insertions, 0 deletions

diff --git a/test/passes/optimize-instructions.wast b/test/passes/optimize-instructions.wast
index b65432715..aa979c62a 100644
--- a/test/passes/optimize-instructions.wast
+++ b/test/passes/optimize-instructions.wast
@@ -3479,6 +3479,53 @@
       )
     )
   )
+  (func $getFallthrough ;; unit tests for Properties::getFallthrough
+    (local $x0 i32)
+    (local $x1 i32)
+    (local $x2 i32)
+    (local $x3 i32)
+    (local $x4 i32)
+    (local $x5 i32)
+    (local $x6 i32)
+    (local $x7 i32)
+    ;; the trivial case
+    (set_local $x0 (i32.const 1))
+    (drop (i32.and (get_local $x0) (i32.const 7)))
+    ;; tees
+    (set_local $x1 (tee_local $x2 (i32.const 1)))
+    (drop (i32.and (get_local $x1) (i32.const 7)))
+    ;; loop
+    (set_local $x3 (loop (result i32) (i32.const 1)))
+    (drop (i32.and (get_local $x3) (i32.const 7)))
+    ;; if - two sides, can't
+    (set_local $x4 (if (result i32) (i32.const 1) (i32.const 2) (i32.const 3)))
+    (drop (i32.and (get_local $x4) (i32.const 7)))
+    ;; if - one side, can
+    (set_local $x5 (if (result i32) (i32.const 1) (unreachable) (i32.const 3)))
+    (drop (i32.and (get_local $x5) (i32.const 7)))
+    ;; if - one side, can
+    (set_local $x6 (if (result i32) (i32.const 1) (i32.const 3) (unreachable)))
+    (drop (i32.and (get_local $x6) (i32.const 7)))
+    ;; br_if with value
+    (drop
+      (block $out (result i32)
+        (set_local $x7 (br_if $out (i32.const 1) (i32.const 1)))
+        (drop (i32.and (get_local $x7) (i32.const 7)))
+        (unreachable)
+      )
+    )
+  )
+  (func $tee-with-unreachable-value (result f64)
+   (local $var$0 i32)
+   (block $label$1 (result f64)
+    (tee_local $var$0
+     (br_if $label$1 ;; the f64 does not actually flow through this, it's unreachable (and the type is wrong - but unchecked)
+      (f64.const 1)
+      (unreachable)
+     )
+    )
+   )
+  )
 )
 (module
   (import "env" "memory" (memory $0 (shared 256 256)))