From 284c49c36faea2f813f66d9ddf861a45a2a4c422 Mon Sep 17 00:00:00 2001
From: David Majnemer <david.majnemer@gmail.com>
Date: Wed, 1 Jul 2015 05:37:57 +0000
Subject: [PATCH] [SCCP] Turn loads of null into undef instead of zero
 initialized values

Surprisingly, this is a correctness issue: the mmx type exists for
calling convention purposes, LLVM doesn't have a zero representation for
them.

This partially fixes PR23999.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@241142 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/SCCP.cpp | 2 +-
 test/Transforms/SCCP/crash.ll  | 5 +++++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/lib/Transforms/Scalar/SCCP.cpp b/lib/Transforms/Scalar/SCCP.cpp
index bc068f78c57..305175ff8f7 100644
--- a/lib/Transforms/Scalar/SCCP.cpp
+++ b/lib/Transforms/Scalar/SCCP.cpp
@@ -1055,7 +1055,7 @@ void SCCPSolver::visitLoadInst(LoadInst &I) {
 
   // load null -> null
   if (isa<ConstantPointerNull>(Ptr) && I.getPointerAddressSpace() == 0)
-    return markConstant(IV, &I, Constant::getNullValue(I.getType()));
+    return markConstant(IV, &I, UndefValue::get(I.getType()));
 
   // Transform load (constant global) into the value loaded.
   if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
diff --git a/test/Transforms/SCCP/crash.ll b/test/Transforms/SCCP/crash.ll
index 88528902d72..3ec1fd21745 100644
--- a/test/Transforms/SCCP/crash.ll
+++ b/test/Transforms/SCCP/crash.ll
@@ -27,3 +27,8 @@ define i32 @test2([4 x i32] %A) {
   %B = extractvalue [4 x i32] %A, 1
   ret i32 %B
 }
+
+define x86_mmx @test3() {
+  %load = load x86_mmx, x86_mmx* null
+  ret x86_mmx %load
+}
-- 
2.34.1