Sink dag combine's post index load / store code that swap base ptr and index into the target hook. Only the target knows whether the swap is safe. In Thumb2 mode, the offset must be an immediate. rdar://7998649

llvm-svn: 104060

1 files changed, 15 insertions, 1 deletions

diff --git a/llvm/lib/Target/ARM/ARMISelLowering.cpp b/llvm/lib/Target/ARM/ARMISelLowering.cpp
index c284a7e0439..f5373cb0e7f 100644
--- a/llvm/lib/Target/ARM/ARMISelLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMISelLowering.cpp
@@ -4407,9 +4407,11 @@ bool ARMTargetLowering::getPostIndexedAddressParts(SDNode *N, SDNode *Op,
   bool isSEXTLoad = false;
   if (LoadSDNode *LD = dyn_cast<LoadSDNode>(N)) {
     VT  = LD->getMemoryVT();
+    Ptr = LD->getBasePtr();
     isSEXTLoad = LD->getExtensionType() == ISD::SEXTLOAD;
   } else if (StoreSDNode *ST = dyn_cast<StoreSDNode>(N)) {
     VT  = ST->getMemoryVT();
+    Ptr = ST->getBasePtr();
   } else
     return false;
 
@@ -4417,13 +4419,25 @@ bool ARMTargetLowering::getPostIndexedAddressParts(SDNode *N, SDNode *Op,
   bool isLegal = false;
   if (Subtarget->isThumb2())
     isLegal = getT2IndexedAddressParts(Op, VT, isSEXTLoad, Base, Offset,
-                                        isInc, DAG);
+                                       isInc, DAG);
   else
     isLegal = getARMIndexedAddressParts(Op, VT, isSEXTLoad, Base, Offset,
                                         isInc, DAG);
   if (!isLegal)
     return false;
 
+  if (Ptr != Base) {
+    // Swap base ptr and offset to catch more post-index load / store when
+    // it's legal. In Thumb2 mode, offset must be an immediate.
+    if (Ptr == Offset && Op->getOpcode() == ISD::ADD &&
+        !Subtarget->isThumb2())
+      std::swap(Base, Offset);
+
+    // Post-indexed load / store update the base pointer.
+    if (Ptr != Base)
+      return false;
+  }
+
   AM = isInc ? ISD::POST_INC : ISD::POST_DEC;
   return true;
 }