Add the llvm.frameallocate and llvm.recoverframeallocation intrinsics

These intrinsics allow multiple functions to share a single stack
allocation from one function's call frame. The function with the
allocation may only perform one allocation, and it must be in the entry
block.

Functions accessing the allocation call llvm.recoverframeallocation with
the function whose frame they are accessing and a frame pointer from an
active call frame of that function.

These intrinsics are very difficult to inline correctly, so the
intention is that they be introduced rarely, or at least very late
during EH preparation.

Reviewers: echristo, andrew.w.kaylor

Differential Revision: http://reviews.llvm.org/D6493

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225746 91177308-0d34-0410-b5e6-96231b3b80d8

5 files changed, 90 insertions, 0 deletions

diff --git a/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index 461b6d272da..bbed8081a14 100644
--- a/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -748,6 +748,16 @@ void AsmPrinter::emitCFIInstruction(const MachineInstr &MI) {
   emitCFIInstruction(CFI);
 }
 
+void AsmPrinter::emitFrameAlloc(const MachineInstr &MI) {
+  // The operands are the MCSymbol and the frame offset of the allocation.
+  MCSymbol *FrameAllocSym = MI.getOperand(0).getMCSymbol();
+  int FrameOffset = MI.getOperand(1).getImm();
+
+  // Emit a symbol assignment.
+  OutStreamer.EmitAssignment(FrameAllocSym,
+                             MCConstantExpr::Create(FrameOffset, OutContext));
+}
+
 /// EmitFunctionBody - This method emits the body and trailer for a
 /// function.
 void AsmPrinter::EmitFunctionBody() {
@@ -786,6 +796,10 @@ void AsmPrinter::EmitFunctionBody() {
         emitCFIInstruction(MI);
         break;
 
+      case TargetOpcode::FRAME_ALLOC:
+        emitFrameAlloc(MI);
+        break;
+
       case TargetOpcode::EH_LABEL:
       case TargetOpcode::GC_LABEL:
         OutStreamer.EmitLabel(MI.getOperand(0).getMCSymbol());
diff --git a/lib/CodeGen/DeadMachineInstructionElim.cpp b/lib/CodeGen/DeadMachineInstructionElim.cpp
index 48213c12e04..c17a35d1c73 100644
--- a/lib/CodeGen/DeadMachineInstructionElim.cpp
+++ b/lib/CodeGen/DeadMachineInstructionElim.cpp
@@ -59,6 +59,10 @@ bool DeadMachineInstructionElim::isDead(const MachineInstr *MI) const {
   if (MI->isInlineAsm())
     return false;
 
+  // Don't delete frame allocation labels.
+  if (MI->getOpcode() == TargetOpcode::FRAME_ALLOC)
+    return false;
+
   // Don't delete instructions with side effects.
   bool SawStore = false;
   if (!MI->isSafeToMove(TII, nullptr, SawStore) && !MI->isPHI())
diff --git a/lib/CodeGen/MachineFunction.cpp b/lib/CodeGen/MachineFunction.cpp
index 8a2b610948b..6b4cba6c678 100644
--- a/lib/CodeGen/MachineFunction.cpp
+++ b/lib/CodeGen/MachineFunction.cpp
@@ -587,6 +587,14 @@ int MachineFrameInfo::CreateFixedSpillStackObject(uint64_t Size,
   return -++NumFixedObjects;
 }
 
+int MachineFrameInfo::CreateFrameAllocation(uint64_t Size) {
+  // Force the use of a frame pointer. The intention is that this intrinsic be
+  // used in conjunction with unwind mechanisms that leak the frame pointer.
+  setFrameAddressIsTaken(true);
+  Size = RoundUpToAlignment(Size, StackAlignment);
+  return CreateStackObject(Size, StackAlignment, false);
+}
+
 BitVector
 MachineFrameInfo::getPristineRegs(const MachineBasicBlock *MBB) const {
   assert(MBB && "MBB must be valid");
diff --git a/lib/CodeGen/PrologEpilogInserter.cpp b/lib/CodeGen/PrologEpilogInserter.cpp
index f5f32abc0e4..385e5a35afb 100644
--- a/lib/CodeGen/PrologEpilogInserter.cpp
+++ b/lib/CodeGen/PrologEpilogInserter.cpp
@@ -817,6 +817,17 @@ void PEI::replaceFrameIndices(MachineBasicBlock *BB, MachineFunction &Fn,
         continue;
       }
 
+      // Frame allocations are target independent. Simply swap the index with
+      // the offset.
+      if (MI->getOpcode() == TargetOpcode::FRAME_ALLOC) {
+        assert(TFI->hasFP(Fn) && "frame alloc requires FP");
+        MachineOperand &FI = MI->getOperand(i);
+        unsigned Reg;
+        int FrameOffset = TFI->getFrameIndexReference(Fn, FI.getIndex(), Reg);
+        FI.ChangeToImmediate(FrameOffset);
+        continue;
+      }
+
       // Some instructions (e.g. inline asm instructions) can have
       // multiple frame indices and/or cause eliminateFrameIndex
       // to insert more than one instruction. We need the register
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index e1396649f34..8a762555577 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -48,6 +48,7 @@
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/Statepoint.h"
+#include "llvm/MC/MCSymbol.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorHandling.h"
@@ -5581,6 +5582,58 @@ SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I, unsigned Intrinsic) {
   }
   case Intrinsic::instrprof_increment:
     llvm_unreachable("instrprof failed to lower an increment");
+
+  case Intrinsic::frameallocate: {
+    MachineFunction &MF = DAG.getMachineFunction();
+    const TargetInstrInfo *TII = DAG.getSubtarget().getInstrInfo();
+
+    // Do the allocation and map it as a normal value.
+    // FIXME: Maybe we should add this to the alloca map so that we don't have
+    // to register allocate it?
+    uint64_t Size = cast<ConstantInt>(I.getArgOperand(0))->getZExtValue();
+    int Alloc = MF.getFrameInfo()->CreateFrameAllocation(Size);
+    MVT PtrVT = TLI.getPointerTy(0);
+    SDValue FIVal = DAG.getFrameIndex(Alloc, PtrVT);
+    setValue(&I, FIVal);
+
+    // Directly emit a FRAME_ALLOC machine instr. Label assignment emission is
+    // the same on all targets.
+    MCSymbol *FrameAllocSym =
+        MF.getMMI().getContext().getOrCreateFrameAllocSymbol(MF.getName());
+    BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, dl,
+            TII->get(TargetOpcode::FRAME_ALLOC))
+        .addSym(FrameAllocSym)
+        .addFrameIndex(Alloc);
+
+    return nullptr;
+  }
+
+  case Intrinsic::recoverframeallocation: {
+    // i8* @llvm.recoverframeallocation(i8* %fn, i8* %fp)
+    MachineFunction &MF = DAG.getMachineFunction();
+    MVT PtrVT = TLI.getPointerTy(0);
+
+    // Get the symbol that defines the frame offset.
+    Function *Fn = cast<Function>(I.getArgOperand(0)->stripPointerCasts());
+    MCSymbol *FrameAllocSym =
+        MF.getMMI().getContext().getOrCreateFrameAllocSymbol(Fn->getName());
+
+    // Create a TargetExternalSymbol for the label to avoid any target lowering
+    // that would make this PC relative.
+    StringRef Name = FrameAllocSym->getName();
+    assert(Name.size() == strlen(Name.data()) && "not null terminated");
+    SDValue OffsetSym = DAG.getTargetExternalSymbol(Name.data(), PtrVT);
+    SDValue OffsetVal =
+        DAG.getNode(ISD::RECOVER_FRAME_ALLOC, sdl, PtrVT, OffsetSym);
+
+    // Add the offset to the FP.
+    Value *FP = I.getArgOperand(1);
+    SDValue FPVal = getValue(FP);
+    SDValue Add = DAG.getNode(ISD::ADD, sdl, PtrVT, FPVal, OffsetVal);
+    setValue(&I, Add);
+
+    return nullptr;
+  }
   }
 }