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.

2 files changed, 138 insertions, 0 deletions

diff --git a/test/passes/optimize-instructions.txt b/test/passes/optimize-instructions.txt
index 0b156f803..5a0a45e3d 100644
--- a/test/passes/optimize-instructions.txt
+++ b/test/passes/optimize-instructions.txt
@@ -11,6 +11,7 @@
  (type $9 (func (param i32 i64 f32 f64)))
  (type $10 (func (param i32 i64 f32)))
  (type $11 (func (param i32 i64 f64 i32)))
+ (type $12 (func (result f64)))
  (memory $0 0)
  (export "load-off-2" (func $load-off-2))
  (func $f (; 0 ;) (type $0) (param $i1 i32) (param $i2 i64)
@@ -2906,6 +2907,96 @@
    )
   )
  )
+ (func $getFallthrough (; 71 ;) (type $1)
+  (local $x0 i32)
+  (local $x1 i32)
+  (local $x2 i32)
+  (local $x3 i32)
+  (local $x4 i32)
+  (local $x5 i32)
+  (local $x6 i32)
+  (local $x7 i32)
+  (set_local $x0
+   (i32.const 1)
+  )
+  (drop
+   (get_local $x0)
+  )
+  (set_local $x1
+   (tee_local $x2
+    (i32.const 1)
+   )
+  )
+  (drop
+   (get_local $x1)
+  )
+  (set_local $x3
+   (loop $loop-in (result i32)
+    (i32.const 1)
+   )
+  )
+  (drop
+   (get_local $x3)
+  )
+  (set_local $x4
+   (if (result i32)
+    (i32.const 1)
+    (i32.const 2)
+    (i32.const 3)
+   )
+  )
+  (drop
+   (i32.and
+    (get_local $x4)
+    (i32.const 7)
+   )
+  )
+  (set_local $x5
+   (if (result i32)
+    (i32.const 1)
+    (unreachable)
+    (i32.const 3)
+   )
+  )
+  (drop
+   (get_local $x5)
+  )
+  (set_local $x6
+   (if (result i32)
+    (i32.const 1)
+    (i32.const 3)
+    (unreachable)
+   )
+  )
+  (drop
+   (get_local $x6)
+  )
+  (drop
+   (block $out (result i32)
+    (set_local $x7
+     (br_if $out
+      (i32.const 1)
+      (i32.const 1)
+     )
+    )
+    (drop
+     (get_local $x7)
+    )
+    (unreachable)
+   )
+  )
+ )
+ (func $tee-with-unreachable-value (; 72 ;) (type $12) (result f64)
+  (local $var$0 i32)
+  (block $label$1 (result f64)
+   (tee_local $var$0
+    (br_if $label$1
+     (f64.const 1)
+     (unreachable)
+    )
+   )
+  )
+ )
 )
 (module
  (type $0 (func))
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)))