[RISCV] Support lowering FrameIndex

Introduces the AddrFI "addressing mode", which is necessary simply because 
it's not possible to write a pattern that directly matches a frameindex.

Ensure callee-saved registers are accessed relative to the stackpointer. This
is necessary as callee-saved register spills are performed before the frame
pointer is set.

Move HexagonDAGToDAGISel::isOrEquivalentToAdd to SelectionDAGISel, so we can 
make use of it in the RISC-V backend.

Differential Revision: https://reviews.llvm.org/D39848

llvm-svn: 320353

1 files changed, 29 insertions, 0 deletions

diff --git a/llvm/lib/Target/RISCV/RISCVFrameLowering.cpp b/llvm/lib/Target/RISCV/RISCVFrameLowering.cpp
index fd3b258e26c..cd18a104631 100644
--- a/llvm/lib/Target/RISCV/RISCVFrameLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVFrameLowering.cpp
@@ -27,3 +27,32 @@ void RISCVFrameLowering::emitPrologue(MachineFunction &MF,
 
 void RISCVFrameLowering::emitEpilogue(MachineFunction &MF,
                                       MachineBasicBlock &MBB) const {}
+
+int RISCVFrameLowering::getFrameIndexReference(const MachineFunction &MF,
+                                               int FI,
+                                               unsigned &FrameReg) const {
+  const MachineFrameInfo &MFI = MF.getFrameInfo();
+  const TargetRegisterInfo *RI = MF.getSubtarget().getRegisterInfo();
+
+  // Callee-saved registers should be referenced relative to the stack
+  // pointer (positive offset), otherwise use the frame pointer (negative
+  // offset).
+  const std::vector<CalleeSavedInfo> &CSI = MFI.getCalleeSavedInfo();
+  int MinCSFI = 0;
+  int MaxCSFI = -1;
+
+  int Offset = MFI.getObjectOffset(FI) - getOffsetOfLocalArea() +
+               MFI.getOffsetAdjustment();
+
+  if (CSI.size()) {
+    MinCSFI = CSI[0].getFrameIdx();
+    MaxCSFI = CSI[CSI.size() - 1].getFrameIdx();
+  }
+
+  FrameReg = RI->getFrameRegister(MF);
+  if (FI >= MinCSFI && FI <= MaxCSFI) {
+    FrameReg = RISCV::X2;
+    Offset += MF.getFrameInfo().getStackSize();
+  }
+  return Offset;
+}