Don't move normal loads across volatile/atomic loads.
It is technically allowed to move a normal load across a volatile load,
but probably not a good idea.
It is not allowed to move a load across an atomic load with
Ordering > Monotonic, and we model those with MOVolatile as well.
I recently removed the mayStore flag from atomic load instructions, so
they don't need a pseudo-opcode. This patch makes up for the difference.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@162857 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/MachineInstr.cpp b/lib/CodeGen/MachineInstr.cpp
index bfb722b..7ff79b3 100644
--- a/lib/CodeGen/MachineInstr.cpp
+++ b/lib/CodeGen/MachineInstr.cpp
@@ -1343,7 +1343,12 @@
AliasAnalysis *AA,
bool &SawStore) const {
// Ignore stuff that we obviously can't move.
- if (mayStore() || isCall()) {
+ //
+ // Treat volatile loads as stores. This is not strictly necessary for
+ // volatiles, but it is required for atomic loads. It is now allowed to move
+ // a load across an atomic load with Ordering > Monotonic.
+ if (mayStore() || isCall() ||
+ (mayLoad() && hasVolatileMemoryRef())) {
SawStore = true;
return false;
}
@@ -1359,8 +1364,8 @@
// load.
if (mayLoad() && !isInvariantLoad(AA))
// Otherwise, this is a real load. If there is a store between the load and
- // end of block, or if the load is volatile, we can't move it.
- return !SawStore && !hasVolatileMemoryRef();
+ // end of block, we can't move it.
+ return !SawStore;
return true;
}