Fix a DataFlowOpts bug (#1729)

We create some fake nodes for internal use, and were looking at one by mistake. This fixes that by

* Creating a non-ambiguous fake node, a call (which represents an unknown value properly, unlike a zero which we had before).
* Make DFO not rely on those values, if it knows a node is constant, apply those constant values.
Found by the fuzzer.

2 files changed, 21 insertions, 0 deletions

diff --git a/test/passes/flatten_dfo_O3.txt b/test/passes/flatten_dfo_O3.txt
index 02cdbfa86..c0e8a8811 100644
--- a/test/passes/flatten_dfo_O3.txt
+++ b/test/passes/flatten_dfo_O3.txt
@@ -3,12 +3,14 @@
  (type $1 (func (param i32 i32) (result i32)))
  (type $2 (func (param i64 i32) (result f64)))
  (type $3 (func (param f64) (result f64)))
+ (type $4 (func (result i32)))
  (memory $0 (shared 1 1))
  (export "one" (func $0))
  (export "two" (func $1))
  (export "use-var" (func $2))
  (export "bad1" (func $3))
  (export "only-dfo" (func $4))
+ (export "dfo-tee-get" (func $5))
  (func $0 (; 0 ;) (; has Stack IR ;) (type $0)
   (loop $label$2
    (block $label$3
@@ -47,4 +49,7 @@
    (br $label$1)
   )
  )
+ (func $5 (; 5 ;) (; has Stack IR ;) (type $4) (result i32)
+  (i32.const 1)
+ )
 )
diff --git a/test/passes/flatten_dfo_O3.wast b/test/passes/flatten_dfo_O3.wast
index 512315995..7ba5a2fd6 100644
--- a/test/passes/flatten_dfo_O3.wast
+++ b/test/passes/flatten_dfo_O3.wast
@@ -183,5 +183,21 @@
    (br $label$1)
   )
  )
+ (func "dfo-tee-get" (result i32)
+  (local $0 i32)
+  (if (result i32)
+   (tee_local $0
+    (i32.const 1)
+   )
+   (loop $label$2 (result i32)
+    (select
+     (i32.const 1)
+     (i32.const -1709605511)
+     (get_local $0)
+    )
+   )
+   (unreachable)
+  )
+ )
 )