Make load->store deletion a bit smarter. This allows us to compile this:
void test(long long *P) { *P ^= 1; }
into just:
_test:
movl 4(%esp), %eax
xorl $1, (%eax)
ret
instead of code like this:
_test:
movl 4(%esp), %ecx
xorl $1, (%ecx)
movl 4(%ecx), %edx
movl %edx, 4(%ecx)
ret
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@45762 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index e581ed3..0bb11fa 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -4122,6 +4122,34 @@
return SDOperand();
}
+/// ReachesChainWithoutSideEffects - Do a little local search to see if Src can
+/// reach Dest without any side effects like a store, or call. Non-volatile
+/// loads are ok though.
+static bool ReachesChainWithoutSideEffects(SDOperand Src, SDOperand Dest,
+ unsigned Depth = 0) {
+ if (Src == Dest) return true;
+
+ // Don't search too deeply, we just want to be able to see through
+ // TokenFactor's etc.
+ if (Depth == 2) return false;
+
+ // If this is a token factor, all inputs to the TF happen in parallel. If any
+ // of the operands of the TF reach dest, then we can do the xform.
+ if (Src.getOpcode() == ISD::TokenFactor) {
+ for (unsigned i = 0, e = Src.getNumOperands(); i != e; ++i)
+ if (ReachesChainWithoutSideEffects(Src.getOperand(i), Dest, Depth+1))
+ return true;
+ return false;
+ }
+
+ // Loads don't have side effects, look through them.
+ if (LoadSDNode *Ld = dyn_cast<LoadSDNode>(Src)) {
+ if (!Ld->isVolatile())
+ return ReachesChainWithoutSideEffects(Ld->getChain(), Dest, Depth+1);
+ }
+ return false;
+}
+
SDOperand DAGCombiner::visitSTORE(SDNode *N) {
StoreSDNode *ST = cast<StoreSDNode>(N);
SDOperand Chain = ST->getChain();
@@ -4250,10 +4278,12 @@
// If this is a load followed by a store to the same location, then the store
// is dead/noop.
if (LoadSDNode *Ld = dyn_cast<LoadSDNode>(Value)) {
- if (Chain.Val == Ld && Ld->getBasePtr() == Ptr &&
+ if (Ld->getBasePtr() == Ptr && ST->getStoredVT() == Ld->getLoadedVT() &&
ST->getAddressingMode() == ISD::UNINDEXED &&
- ST->getStoredVT() == Ld->getLoadedVT() &&
- !ST->isVolatile()) {
+ !ST->isVolatile() &&
+ // There can't be any side effects between the load and store, such as
+ // a call or store.
+ ReachesChainWithoutSideEffects(Chain, SDOperand(Ld, 1))) {
// The store is dead, remove it.
return Chain;
}