From 2153c4b8281c1e5f25887ef9183947198c50a9d2 Mon Sep 17 00:00:00 2001
From: Philip Reames <listmail@philipreames.com>
Date: Tue, 19 Mar 2019 17:20:49 +0000
Subject: [PATCH] [AtomicExpand] Fix a crash bug when lowering unordered loads
 to cmpxchg

Add tests for wider atomic loads and stores.  In the process, fix a crasher where we appearently handled unorder stores, but not loads, when lowering to cmpxchg idioms.

llvm-svn: 356482

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Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1797127
       https://github.com/rust-lang/compiler-builtins/issues/338

[ mikhailnov: backported to llvm8, removed tests ]
################################################################

---
diff --git a/llvm/lib/CodeGen/AtomicExpandPass.cpp b/llvm/lib/CodeGen/AtomicExpandPass.cpp
index 10dd21d1ef9d..7a8013abccfb 100644
--- a/llvm/lib/CodeGen/AtomicExpandPass.cpp
+++ b/llvm/lib/CodeGen/AtomicExpandPass.cpp
@@ -431,6 +431,9 @@
 bool AtomicExpand::expandAtomicLoadToCmpXchg(LoadInst *LI) {
   IRBuilder<> Builder(LI);
   AtomicOrdering Order = LI->getOrdering();
+  if (Order == AtomicOrdering::Unordered)
+    Order = AtomicOrdering::Monotonic;
+
   Value *Addr = LI->getPointerOperand();
   Type *Ty = cast<PointerType>(Addr->getType())->getElementType();
   Constant *DummyVal = Constant::getNullValue(Ty);