[ARM] Support constant pools in data when generating execute-only code.

The ARM backend asserts against constant pool lowering when it generates
execute-only code in order to prevent the generation of constant pools in
the text section. It appears that target independent optimizations might
generate DAG nodes that represent constant pools. By lowering such nodes
as global addresses we don't violate the semantics of execute-only code
and also it is guaranteed that execute-only behaves correct with the
position-independent addressing modes that support execute-only code.

Differential Revision: https://reviews.llvm.org/D33773

llvm-svn: 305387

1 files changed, 38 insertions, 15 deletions

diff --git a/llvm/lib/Target/ARM/ARMISelLowering.cpp b/llvm/lib/Target/ARM/ARMISelLowering.cpp
index 5b2d093e8f0..5c48e2a5a92 100644
--- a/llvm/lib/Target/ARM/ARMISelLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMISelLowering.cpp
@@ -2669,12 +2669,34 @@ static SDValue LowerWRITE_REGISTER(SDValue Op, SelectionDAG &DAG) {
 // Select(N) returns N. So the raw TargetGlobalAddress nodes, etc. can only
 // be used to form addressing mode. These wrapped nodes will be selected
 // into MOVi.
-static SDValue LowerConstantPool(SDValue Op, SelectionDAG &DAG) {
+SDValue ARMTargetLowering::LowerConstantPool(SDValue Op,
+                                             SelectionDAG &DAG) const {
   EVT PtrVT = Op.getValueType();
   // FIXME there is no actual debug info here
   SDLoc dl(Op);
   ConstantPoolSDNode *CP = cast<ConstantPoolSDNode>(Op);
   SDValue Res;
+
+  // When generating execute-only code Constant Pools must be promoted to the
+  // global data section. It's a bit ugly that we can't share them across basic
+  // blocks, but this way we guarantee that execute-only behaves correct with
+  // position-independent addressing modes.
+  if (Subtarget->genExecuteOnly()) {
+    auto AFI = DAG.getMachineFunction().getInfo<ARMFunctionInfo>();
+    auto T = const_cast<Type*>(CP->getType());
+    auto C = const_cast<Constant*>(CP->getConstVal());
+    auto M = const_cast<Module*>(DAG.getMachineFunction().
+                                 getFunction()->getParent());
+    auto L = Twine(DAG.getDataLayout().getPrivateGlobalPrefix()) + "CP" +
+             Twine(DAG.getMachineFunction().getFunctionNumber()) + "_" +
+             Twine(AFI->createPICLabelUId());
+    auto GV = new GlobalVariable(*M, T, /*isConstant=*/true,
+                                 GlobalVariable::InternalLinkage, C, L);
+    SDValue GA = DAG.getTargetGlobalAddress(dyn_cast<GlobalValue>(GV),
+                                            dl, PtrVT);
+    return LowerGlobalAddress(GA, DAG);
+  }
+
   if (CP->isMachineConstantPoolEntry())
     Res = DAG.getTargetConstantPool(CP->getMachineCPVal(), PtrVT,
                                     CP->getAlignment());
@@ -3118,6 +3140,19 @@ static bool isReadOnly(const GlobalValue *GV) {
          isa<Function>(GV);
 }
 
+SDValue ARMTargetLowering::LowerGlobalAddress(SDValue Op,
+                                              SelectionDAG &DAG) const {
+  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);
+  }
+}
+
 SDValue ARMTargetLowering::LowerGlobalAddressELF(SDValue Op,
                                                  SelectionDAG &DAG) const {
   EVT PtrVT = getPointerTy(DAG.getDataLayout());
@@ -7634,21 +7669,9 @@ SDValue ARMTargetLowering::LowerOperation(SDValue Op, SelectionDAG &DAG) const {
   switch (Op.getOpcode()) {
   default: llvm_unreachable("Don't know how to custom lower this!");
   case ISD::WRITE_REGISTER: return LowerWRITE_REGISTER(Op, DAG);
-  case ISD::ConstantPool:
-    if (Subtarget->genExecuteOnly())
-      llvm_unreachable("execute-only should not generate constant pools");
-    return LowerConstantPool(Op, DAG);
+  case ISD::ConstantPool: return LowerConstantPool(Op, DAG);
   case ISD::BlockAddress:  return LowerBlockAddress(Op, DAG);
-  case ISD::GlobalAddress:
-    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::GlobalAddress: return LowerGlobalAddress(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);