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Don't move normal loads across volatile/atomic loads.

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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
This commit is contained in:
Jakob Stoklund Olesen 2012-08-29 20:48:45 +00:00
parent 688c1cd6c9
commit 0d75858395
1 changed files with 8 additions and 3 deletions
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11
lib/CodeGen/MachineInstr.cpp
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@ -1343,7 +1343,12 @@ bool MachineInstr::isSafeToMove(const TargetInstrInfo *TII,
AliasAnalysis *AA, AliasAnalysis *AA,
bool &SawStore) const { bool &SawStore) const {
// Ignore stuff that we obviously can't move. // 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; SawStore = true;
return false; return false;
} }
@ -1359,8 +1364,8 @@ bool MachineInstr::isSafeToMove(const TargetInstrInfo *TII,
// load. // load.
if (mayLoad() && !isInvariantLoad(AA)) if (mayLoad() && !isInvariantLoad(AA))
// Otherwise, this is a real load. If there is a store between the load and // 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. // end of block, we can't move it.
return !SawStore && !hasVolatileMemoryRef(); return !SawStore;
return true; return true;
} }