Fix swapped BasePtr and Offset in pre-inc memory addresses.

PPCTargetLowering::getPreIndexedAddressParts currently provides
the base part of a memory address in the offset result, and the
offset part in the base result.  That swap is then undone again
when an MI instruction is generated (in PPCDAGToDAGISel::Select
for loads, and using .md Pat patterns for stores).

This patch reverts this double swap, to make common code and
back-end be in sync as to which part of the address is base
and which is offset.

To avoid performance regressions in certain cases, target code
now checks whether the choice of base register would be rejected
for pre-inc accesses by common code, and attempts to swap base
and offset again in such cases.  (Overall, this means that now
pre-ice accesses are generated *more* frequently than before.)



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@177733 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 21 insertions, 1 deletions

diff --git a/lib/Target/PowerPC/PPCISelLowering.cpp b/lib/Target/PowerPC/PPCISelLowering.cpp
index c7d454692e..218a20db57 100644
--- a/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -1192,6 +1192,7 @@ bool PPCTargetLowering::getPreIndexedAddressParts(SDNode *N, SDValue &Base,
                                                   SelectionDAG &DAG) const {
   if (DisablePPCPreinc) return false;
 
+  bool isLoad = true;
   SDValue Ptr;
   EVT VT;
   unsigned Alignment;
@@ -1203,6 +1204,7 @@ bool PPCTargetLowering::getPreIndexedAddressParts(SDNode *N, SDValue &Base,
     Ptr = ST->getBasePtr();
     VT  = ST->getMemoryVT();
     Alignment = ST->getAlignment();
+    isLoad = false;
   } else
     return false;
 
@@ -1210,7 +1212,25 @@ bool PPCTargetLowering::getPreIndexedAddressParts(SDNode *N, SDValue &Base,
   if (VT.isVector())
     return false;
 
-  if (SelectAddressRegReg(Ptr, Offset, Base, DAG)) {
+  if (SelectAddressRegReg(Ptr, Base, Offset, DAG)) {
+
+    // Common code will reject creating a pre-inc form if the base pointer
+    // is a frame index, or if N is a store and the base pointer is either
+    // the same as or a predecessor of the value being stored.  Check for
+    // those situations here, and try with swapped Base/Offset instead.
+    bool Swap = false;
+
+    if (isa<FrameIndexSDNode>(Base) || isa<RegisterSDNode>(Base))
+      Swap = true;
+    else if (!isLoad) {
+      SDValue Val = cast<StoreSDNode>(N)->getValue();
+      if (Val == Base || Base.getNode()->isPredecessorOf(Val.getNode()))
+        Swap = true;
+    }
+
+    if (Swap)
+      std::swap(Base, Offset);
+
     AM = ISD::PRE_INC;
     return true;
   }