From 74d614a6fc97587c2092807edf5382163d6d1dc6 Mon Sep 17 00:00:00 2001
From: Saleem Abdulrasool <compnerd@compnerd.org>
Date: Fri, 9 May 2014 00:58:32 +0000
Subject: [PATCH] ARM: support PIC on Windows on ARM

Handle lowering of global addresses for PIC mode compilation on Windows.  Always
use the movw/movt load to load the address as Windows on ARM requires ARMv7+ and
is a pure Thumb environment.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208385 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Target/ARM/ARMISelLowering.cpp | 28 ++++++++++++++++++++++++++--
 lib/Target/ARM/ARMISelLowering.h   |  1 +
 test/CodeGen/ARM/Windows/pic.ll    | 16 ++++++++++++++++
 3 files changed, 43 insertions(+), 2 deletions(-)
 create mode 100644 test/CodeGen/ARM/Windows/pic.ll

diff --git a/lib/Target/ARM/ARMISelLowering.cpp b/lib/Target/ARM/ARMISelLowering.cpp
index 8f410b702c5..925b4693fd5 100644
--- a/lib/Target/ARM/ARMISelLowering.cpp
+++ b/lib/Target/ARM/ARMISelLowering.cpp
@@ -2485,6 +2485,23 @@ SDValue ARMTargetLowering::LowerGlobalAddressDarwin(SDValue Op,
   return Result;
 }
 
+SDValue ARMTargetLowering::LowerGlobalAddressWindows(SDValue Op,
+                                                     SelectionDAG &DAG) const {
+  assert(Subtarget->isTargetWindows() && "non-Windows COFF is not supported");
+  assert(Subtarget->useMovt() && "Windows on ARM expects to use movw/movt");
+
+  const GlobalValue *GV = cast<GlobalAddressSDNode>(Op)->getGlobal();
+  EVT PtrVT = getPointerTy();
+  SDLoc DL(Op);
+
+  ++NumMovwMovt;
+
+  // FIXME: Once remat is capable of dealing with instructions with register
+  // operands, expand this into two nodes.
+  return DAG.getNode(ARMISD::Wrapper, DL, PtrVT,
+                     DAG.getTargetGlobalAddress(GV, DL, PtrVT));
+}
+
 SDValue ARMTargetLowering::LowerGLOBAL_OFFSET_TABLE(SDValue Op,
                                                     SelectionDAG &DAG) const {
   assert(Subtarget->isTargetELF() &&
@@ -6050,8 +6067,15 @@ SDValue ARMTargetLowering::LowerOperation(SDValue Op, SelectionDAG &DAG) const {
   case ISD::ConstantPool:  return LowerConstantPool(Op, DAG);
   case ISD::BlockAddress:  return LowerBlockAddress(Op, DAG);
   case ISD::GlobalAddress:
-    return Subtarget->isTargetMachO() ? LowerGlobalAddressDarwin(Op, DAG) :
-      LowerGlobalAddressELF(Op, DAG);
+    switch (Subtarget->getTargetTriple().getObjectFormat()) {
+    default: llvm_unreachable("unknown object format");
+    case Triple::COFF:
+      return LowerGlobalAddressWindows(Op, DAG);
+    case Triple::ELF:
+      return LowerGlobalAddressELF(Op, DAG);
+    case Triple::MachO:
+      return LowerGlobalAddressDarwin(Op, DAG);
+    }
   case ISD::GlobalTLSAddress: return LowerGlobalTLSAddress(Op, DAG);
   case ISD::SELECT:        return LowerSELECT(Op, DAG);
   case ISD::SELECT_CC:     return LowerSELECT_CC(Op, DAG);
diff --git a/lib/Target/ARM/ARMISelLowering.h b/lib/Target/ARM/ARMISelLowering.h
index 7f28a251f52..cff7a9799a8 100644
--- a/lib/Target/ARM/ARMISelLowering.h
+++ b/lib/Target/ARM/ARMISelLowering.h
@@ -437,6 +437,7 @@ namespace llvm {
     SDValue LowerBlockAddress(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerGlobalAddressDarwin(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerGlobalAddressELF(SDValue Op, SelectionDAG &DAG) const;
+    SDValue LowerGlobalAddressWindows(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerGlobalTLSAddress(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerToTLSGeneralDynamicModel(GlobalAddressSDNode *GA,
                                             SelectionDAG &DAG) const;
diff --git a/test/CodeGen/ARM/Windows/pic.ll b/test/CodeGen/ARM/Windows/pic.ll
new file mode 100644
index 00000000000..28d371f4521
--- /dev/null
+++ b/test/CodeGen/ARM/Windows/pic.ll
@@ -0,0 +1,16 @@
+; RUN: llc -mtriple thumbv7-windows-itanium -relocation-model pic -filetype asm -o - %s \
+; RUN:    | FileCheck %s
+
+@external = external global i8
+
+define arm_aapcs_vfpcc i8 @return_external() {
+entry:
+  %0 = load i8* @external, align 1
+  ret i8 %0
+}
+
+; CHECK-LABEL: return_external
+; CHECK: movw r0, :lower16:external
+; CHECK: movt r0, :upper16:external
+; CHECK: ldrb r0, [r0]
+