Properly handle optimizing out a set from inside the value of another set in SimplifyLocals (#2064)

Details in lengthy comment in the source.

Fixes #2063

2 files changed, 51 insertions, 0 deletions

diff --git a/test/passes/simplify-locals.txt b/test/passes/simplify-locals.txt
new file mode 100644
index 000000000..b743ea528
--- /dev/null
+++ b/test/passes/simplify-locals.txt
@@ -0,0 +1,22 @@
+(module
+ (type $0 (func (result i32)))
+ (func $sink-from-inside (; 0 ;) (type $0) (result i32)
+  (local $0 i32)
+  (local $1 i32)
+  (local $2 i32)
+  (nop)
+  (i32.and
+   (select
+    (i32.const 0)
+    (i32.const 1)
+    (i32.const 1)
+   )
+   (block $block (result i32)
+    (nop)
+    (nop)
+    (nop)
+    (i32.const 1)
+   )
+  )
+ )
+)
diff --git a/test/passes/simplify-locals.wast b/test/passes/simplify-locals.wast
new file mode 100644
index 000000000..3208b76de
--- /dev/null
+++ b/test/passes/simplify-locals.wast
@@ -0,0 +1,29 @@
+(module
+ (func $sink-from-inside (result i32)
+  (local $0 i32)
+  (local $1 i32)
+  (local $2 i32)
+  (local.set $2
+   (block (result i32)
+    (local.set $0
+     (i32.const 1)
+    )
+    (drop
+     (local.get $0)
+    )
+    (local.set $1 ;; after we sink this, must be careful about sinking the parent, to not reorder other things badly
+     (select
+      (i32.const 0)
+      (i32.const 1)
+      (local.get $0)
+     )
+    )
+    (i32.const 1)
+   )
+  )
+  (i32.and
+   (local.get $1)
+   (local.get $2)
+  )
+ )
+)