From 124bdb7497e65f6606635e8ca7adbab0dd2ce07e Mon Sep 17 00:00:00 2001
From: David Majnemer <david.majnemer@gmail.com>
Date: Wed, 25 May 2016 05:53:04 +0000
Subject: [FunctionAttrs] Volatile loads should disable readonly

A volatile load has side effects beyond what callers expect readonly to
signify.  For example, it is not safe to reorder two function calls
which each perform a volatile load to the same memory location.

llvm-svn: 270671
---
 llvm/lib/Transforms/IPO/FunctionAttrs.cpp | 5 +++++
 1 file changed, 5 insertions(+)

(limited to 'llvm/lib/Transforms')

diff --git a/llvm/lib/Transforms/IPO/FunctionAttrs.cpp b/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
index b6ebc632636..c757eb327d0 100644
--- a/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
@@ -463,6 +463,11 @@ determinePointerReadAttrs(Argument *A,
     }
 
     case Instruction::Load:
+      // A volatile load has side effects beyond what readonly can be relied
+      // upon.
+      if (cast<LoadInst>(I)->isVolatile())
+        return Attribute::None;
+
       IsRead = true;
       break;
 
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