1 files changed, 21 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/Scalar/GVN.cpp b/llvm/lib/Transforms/Scalar/GVN.cpp
index 9565dc8c3dc..116dc69b372 100644
--- a/llvm/lib/Transforms/Scalar/GVN.cpp
+++ b/llvm/lib/Transforms/Scalar/GVN.cpp
@@ -1219,6 +1219,7 @@ bool GVN::AnalyzeLoadAvailability(LoadInst *LI, MemDepResult DepInfo,
 
   assert((DepInfo.isDef() || DepInfo.isClobber()) &&
          "expected a local dependence");
+  assert(LI->isUnordered() && "rules below are incorrect for ordered access");
 
   const DataLayout &DL = LI->getModule()->getDataLayout();
 
@@ -1227,7 +1228,8 @@ bool GVN::AnalyzeLoadAvailability(LoadInst *LI, MemDepResult DepInfo,
     // read by the load, we can extract the bits we need for the load from the
     // stored value.
     if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInfo.getInst())) {
-      if (Address) {
+      // Can't forward from non-atomic to atomic without violating memory model.
+      if (Address && LI->isAtomic() <= DepSI->isAtomic()) {
         int Offset =
           AnalyzeLoadFromClobberingStore(LI->getType(), Address, DepSI);
         if (Offset != -1) {
@@ -1244,7 +1246,8 @@ bool GVN::AnalyzeLoadAvailability(LoadInst *LI, MemDepResult DepInfo,
     if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInfo.getInst())) {
       // If this is a clobber and L is the first instruction in its block, then
       // we have the first instruction in the entry block.
-      if (DepLI != LI && Address) {
+      // Can't forward from non-atomic to atomic without violating memory model.
+      if (DepLI != LI && Address && LI->isAtomic() <= DepLI->isAtomic()) {
         int Offset =
           AnalyzeLoadFromClobberingLoad(LI->getType(), Address, DepLI, DL);
 
@@ -1258,7 +1261,7 @@ bool GVN::AnalyzeLoadAvailability(LoadInst *LI, MemDepResult DepInfo,
     // If the clobbering value is a memset/memcpy/memmove, see if we can
     // forward a value on from it.
     if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(DepInfo.getInst())) {
-      if (Address) {
+      if (Address && !LI->isAtomic()) {
         int Offset = AnalyzeLoadFromClobberingMemInst(LI->getType(), Address,
                                                       DepMI, DL);
         if (Offset != -1) {
@@ -1304,6 +1307,10 @@ bool GVN::AnalyzeLoadAvailability(LoadInst *LI, MemDepResult DepInfo,
                                          LI->getType(), DL))
       return false;
 
+    // Can't forward from non-atomic to atomic without violating memory model.
+    if (S->isAtomic() < LI->isAtomic())
+      return false;
+
     Res = AvailableValue::get(S->getValueOperand());
     return true;
   }
@@ -1316,6 +1323,10 @@ bool GVN::AnalyzeLoadAvailability(LoadInst *LI, MemDepResult DepInfo,
         !CanCoerceMustAliasedValueToLoad(LD, LI->getType(), DL))
       return false;
 
+    // Can't forward from non-atomic to atomic without violating memory model.
+    if (LD->isAtomic() < LI->isAtomic())
+      return false;
+
     Res = AvailableValue::getLoad(LD);
     return true;
   }
@@ -1587,6 +1598,11 @@ bool GVN::processNonLocalLoad(LoadInst *LI) {
   if (LI->getParent()->getParent()->hasFnAttribute(Attribute::SanitizeAddress))
     return false;
 
+  // This code hasn't been audited for atomic, ordered, or volatile memory
+  // access.
+  if (!LI->isSimple())
+    return false;
+
   // Step 1: Find the non-local dependencies of the load.
   LoadDepVect Deps;
   MD->getNonLocalPointerDependency(LI, Deps);
@@ -1755,7 +1771,8 @@ bool GVN::processLoad(LoadInst *L) {
   if (!MD)
     return false;
 
-  if (!L->isSimple())
+  // This code hasn't been audited for ordered or volatile memory access
+  if (!L->isUnordered())
     return false;
 
   if (L->use_empty()) {