From cf6c4cff644b87b4c9688931e2924e2d73b9998f Mon Sep 17 00:00:00 2001
From: "Alon Zakai (kripken)" <alonzakai@gmail.com>
Date: Tue, 11 Jul 2017 14:18:52 -0700
Subject: infinite loops have side effects

---
 src/ast/effects.h | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

(limited to 'src')

diff --git a/src/ast/effects.h b/src/ast/effects.h
index a7a5d8fb2..6e4bb617e 100644
--- a/src/ast/effects.h
+++ b/src/ast/effects.h
@@ -39,7 +39,7 @@ struct EffectAnalyzer : public PostWalker<EffectAnalyzer> {
     if (breakNames.size() > 0) branches = true;
   }
 
-  bool branches = false; // branches out of this expression
+  bool branches = false; // branches out of this expression, returns, infinite loops, etc
   bool calls = false;
   std::set<Index> localsRead;
   std::set<Index> localsWritten;
@@ -138,6 +138,18 @@ struct EffectAnalyzer : public PostWalker<EffectAnalyzer> {
   }
   void visitLoop(Loop* curr) {
     if (curr->name.is()) breakNames.erase(curr->name); // these were internal breaks
+    // if the loop is unreachable, then there is branching control flow:
+    //  (1) if the body is unreachable because of a (return), uncaught (br) etc., then we
+    //      already noted branching, so it is ok to mark it again  (if we have *caught*
+    //      (br)s, then they did not lead to the loop body being unreachable).
+    //      (same logic applies to blocks)
+    //  (2) if the loop is unreachable because it only has branches up to the loop
+    //      top, but no way to get out, then it is an infinite loop, and we consider
+    //      that a branching side effect (note how the same logic does not apply to
+    //      blocks).
+    if (curr->type == unreachable) {
+      branches = true;
+    }
   }
 
   void visitCall(Call *curr) { calls = true; }
@@ -182,6 +194,7 @@ struct EffectAnalyzer : public PostWalker<EffectAnalyzer> {
         case TruncUFloat64ToInt32:
         case TruncUFloat64ToInt64: {
           implicitTrap = true;
+          break;
         }
         default: {}
       }
@@ -199,6 +212,7 @@ struct EffectAnalyzer : public PostWalker<EffectAnalyzer> {
         case RemSInt64:
         case RemUInt64: {
           implicitTrap = true;
+          break;
         }
         default: {}
       }
-- 
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