[AArch 64] Use a constant pool load for weak symbol references when

using static relocation model and small code model.

Summary: currently we generate GOT based relocations for weak symbol
references regardless of the underlying relocation model. This should
be change so that in static relocation model we use a constant pool
load instead.

Patch from: Keith Walker

Reviewers: Renato Golin, Tim Northover
llvm-svn: 217503

1 files changed, 21 insertions, 1 deletions

diff --git a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
index db00f8dc84a..91629d30444 100644
--- a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -2711,7 +2711,8 @@ SDValue AArch64TargetLowering::LowerGlobalAddress(SDValue Op,
                                                   SelectionDAG &DAG) const {
   EVT PtrVT = getPointerTy();
   SDLoc DL(Op);
-  const GlobalValue *GV = cast<GlobalAddressSDNode>(Op)->getGlobal();
+  const GlobalAddressSDNode *GN = cast<GlobalAddressSDNode>(Op);
+  const GlobalValue *GV = GN->getGlobal();
   unsigned char OpFlags =
       Subtarget->ClassifyGlobalReference(GV, getTargetMachine());
 
@@ -2726,6 +2727,25 @@ SDValue AArch64TargetLowering::LowerGlobalAddress(SDValue Op,
     return DAG.getNode(AArch64ISD::LOADgot, DL, PtrVT, GotAddr);
   }
 
+  if ((OpFlags & AArch64II::MO_CONSTPOOL) != 0) {
+    assert(getTargetMachine().getCodeModel() == CodeModel::Small &&
+           "use of MO_CONSTPOOL only supported on small model");
+    SDValue Hi = DAG.getTargetConstantPool(GV, PtrVT, 0, 0, AArch64II::MO_PAGE);
+    SDValue ADRP = DAG.getNode(AArch64ISD::ADRP, DL, PtrVT, Hi);
+    unsigned char LoFlags = AArch64II::MO_PAGEOFF | AArch64II::MO_NC;
+    SDValue Lo = DAG.getTargetConstantPool(GV, PtrVT, 0, 0, LoFlags);
+    SDValue PoolAddr = DAG.getNode(AArch64ISD::ADDlow, DL, PtrVT, ADRP, Lo);
+    SDValue GlobalAddr = DAG.getLoad(PtrVT, DL, DAG.getEntryNode(), PoolAddr,
+                                     MachinePointerInfo::getConstantPool(),
+                                     /*isVolatile=*/ false,
+                                     /*isNonTemporal=*/ true,
+                                     /*isInvariant=*/ true, 8);
+    if (GN->getOffset() != 0)
+      return DAG.getNode(ISD::ADD, DL, PtrVT, GlobalAddr,
+                         DAG.getConstant(GN->getOffset(), PtrVT));
+    return GlobalAddr;
+  }
+
   if (getTargetMachine().getCodeModel() == CodeModel::Large) {
     const unsigned char MO_NC = AArch64II::MO_NC;
     return DAG.getNode(