From 18d73c206e8259de61abf54d8d0f47c0e54f42aa Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Mon, 9 Jun 2008 07:58:07 +0000
Subject: [PATCH] Fix PR2411, where ip constant prop would propagate the result
 of a weak function.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@52137 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/IPO/IPConstantPropagation.cpp      |  5 +++++
 .../IPConstantProp/2008-06-09-WeakProp.ll         | 15 +++++++++++++++
 2 files changed, 20 insertions(+)
 create mode 100644 test/Transforms/IPConstantProp/2008-06-09-WeakProp.ll

diff --git a/lib/Transforms/IPO/IPConstantPropagation.cpp b/lib/Transforms/IPO/IPConstantPropagation.cpp
index 792fa980a60..4ebdaf3fb2b 100644
--- a/lib/Transforms/IPO/IPConstantPropagation.cpp
+++ b/lib/Transforms/IPO/IPConstantPropagation.cpp
@@ -147,6 +147,11 @@ bool IPCP::PropagateConstantReturn(Function &F) {
   if (F.getReturnType() == Type::VoidTy)
     return false; // No return value.
 
+  // If this function could be overridden later in the link stage, we can't
+  // propagate information about its results into callers.
+  if (F.hasLinkOnceLinkage() || F.hasWeakLinkage())
+    return false;
+  
   // Check to see if this function returns a constant.
   SmallVector<Value *,4> RetVals;
   const StructType *STy = dyn_cast<StructType>(F.getReturnType());
diff --git a/test/Transforms/IPConstantProp/2008-06-09-WeakProp.ll b/test/Transforms/IPConstantProp/2008-06-09-WeakProp.ll
new file mode 100644
index 00000000000..fc7e3bba38a
--- /dev/null
+++ b/test/Transforms/IPConstantProp/2008-06-09-WeakProp.ll
@@ -0,0 +1,15 @@
+; RUN: llvm-as < %s | opt -ipconstprop | llvm-dis | grep {ret i32 %r}
+; Should not propagate the result of a weak function.
+; PR2411
+
+define weak i32 @foo() nounwind  {
+entry:
+        ret i32 1
+}
+
+define i32 @main() nounwind  {
+entry:
+        %r = call i32 @foo( ) nounwind
+        ret i32 %r
+}
+