[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, 6 insertions, 8 deletions

diff --git a/llvm/lib/Target/RISCV/RISCVRegisterInfo.cpp b/llvm/lib/Target/RISCV/RISCVRegisterInfo.cpp
index 75b277531ce..5776a92cab9 100644
--- a/llvm/lib/Target/RISCV/RISCVRegisterInfo.cpp
+++ b/llvm/lib/Target/RISCV/RISCVRegisterInfo.cpp
@@ -57,22 +57,20 @@ const uint32_t *RISCVRegisterInfo::getNoPreservedMask() const {
 void RISCVRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
                                             int SPAdj, unsigned FIOperandNum,
                                             RegScavenger *RS) const {
-  // TODO: this implementation is a temporary placeholder which does just
-  // enough to allow other aspects of code generation to be tested
-
   assert(SPAdj == 0 && "Unexpected non-zero SPAdj value");
 
   MachineInstr &MI = *II;
   MachineFunction &MF = *MI.getParent()->getParent();
-  const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
   DebugLoc DL = MI.getDebugLoc();
 
-  unsigned FrameReg = getFrameRegister(MF);
   int FrameIndex = MI.getOperand(FIOperandNum).getIndex();
-  int Offset = TFI->getFrameIndexReference(MF, FrameIndex, FrameReg);
-  Offset += MI.getOperand(FIOperandNum + 1).getImm();
+  unsigned FrameReg;
+  int Offset =
+      getFrameLowering(MF)->getFrameIndexReference(MF, FrameIndex, FrameReg) +
+      MI.getOperand(FIOperandNum + 1).getImm();
 
-  assert(TFI->hasFP(MF) && "eliminateFrameIndex currently requires hasFP");
+  assert(MF.getSubtarget().getFrameLowering()->hasFP(MF) &&
+         "eliminateFrameIndex currently requires hasFP");
 
   // Offsets must be directly encoded in a 12-bit immediate field
   if (!isInt<12>(Offset)) {