From 3fe1823a59dc689d081a7a7e327639c20bf51bbc Mon Sep 17 00:00:00 2001
From: Alon Zakai <azakai@google.com>
Date: Fri, 23 Apr 2021 16:09:35 -0700
Subject: OptimizeInstructions: Do not change unreachability in if/select
 changes (#3840)

For example,

(if (result i32)
  (local.get $x)
  (return
    (local.get $y)
  )
  (return
    (local.get $z)
  )
)

If we move the returns outside we'd become unreachable, but we should
not make such type changes in this pass (they are handled by DCE and
Vacuum).

(found by the fuzzer)
---
 test/lit/passes/optimize-instructions.wast | 50 ++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)

(limited to 'test')

diff --git a/test/lit/passes/optimize-instructions.wast b/test/lit/passes/optimize-instructions.wast
index 058c030dd..5b5b44b57 100644
--- a/test/lit/passes/optimize-instructions.wast
+++ b/test/lit/passes/optimize-instructions.wast
@@ -12188,6 +12188,33 @@
       )
     )
   )
+  ;; CHECK:      (func $ternary-identical-arms-return-select (param $x i32) (param $y i32) (param $z i32) (result i32)
+  ;; CHECK-NEXT:  (block $block
+  ;; CHECK-NEXT:   (select
+  ;; CHECK-NEXT:    (return
+  ;; CHECK-NEXT:     (local.get $x)
+  ;; CHECK-NEXT:    )
+  ;; CHECK-NEXT:    (return
+  ;; CHECK-NEXT:     (local.get $y)
+  ;; CHECK-NEXT:    )
+  ;; CHECK-NEXT:    (local.get $z)
+  ;; CHECK-NEXT:   )
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT: )
+  (func $ternary-identical-arms-return-select (param $x i32) (param $y i32) (param $z i32) (result i32)
+    (block $block
+      ;; we cannot optimize a select currently as the return has side effects
+      (select
+        (return
+          (local.get $x)
+        )
+        (return
+          (local.get $y)
+        )
+        (local.get $z)
+      )
+    )
+  )
   ;; CHECK:      (func $send-i32 (param $0 i32)
   ;; CHECK-NEXT:  (nop)
   ;; CHECK-NEXT: )
@@ -12212,4 +12239,27 @@
       )
     )
   )
+  ;; CHECK:      (func $if-dont-change-to-unreachable (param $x i32) (param $y i32) (param $z i32) (result i32)
+  ;; CHECK-NEXT:  (if (result i32)
+  ;; CHECK-NEXT:   (local.get $x)
+  ;; CHECK-NEXT:   (return
+  ;; CHECK-NEXT:    (local.get $y)
+  ;; CHECK-NEXT:   )
+  ;; CHECK-NEXT:   (return
+  ;; CHECK-NEXT:    (local.get $z)
+  ;; CHECK-NEXT:   )
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT: )
+  (func $if-dont-change-to-unreachable (param $x i32) (param $y i32) (param $z i32) (result i32)
+    ;; if we move the returns outside, we'd become unreachable; avoid that.
+    (if (result i32)
+      (local.get $x)
+      (return
+        (local.get $y)
+      )
+      (return
+        (local.get $z)
+      )
+    )
+  )
 )
-- 
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