From 1cfcf17a10898f8c429021c4f78bd9ae61935c52 Mon Sep 17 00:00:00 2001
From: wolfbeast <mcwerewolf@gmail.com>
Date: Wed, 31 Oct 2018 17:30:52 +0100
Subject: Don't mark MGetFirstDollarIndex as movable.

---
 js/src/jit/MIR.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/js/src/jit/MIR.h b/js/src/jit/MIR.h
index 6ec05af76..b2e84322f 100644
--- a/js/src/jit/MIR.h
+++ b/js/src/jit/MIR.h
@@ -8272,7 +8272,10 @@ class MGetFirstDollarIndex
       : MUnaryInstruction(str)
     {
         setResultType(MIRType::Int32);
-        setMovable();
+
+        // Codegen assumes string length > 0 but that's not guaranteed in RegExp.
+        // Don't allow LICM to move this.
+        MOZ_ASSERT(!isMovable());
     }
 
   public:
-- 
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