[Xtensa] Correct use of A7 register, because it maybe used as Frame Pointer and input function argument at the same time.

Author: andreisfr

llvm/lib/Target/Xtensa/XtensaFrameLowering.cpp

@@ -127,6 +127,16 @@ void XtensaFrameLowering::emitPrologue(MachineFunction &MF,
       BuildMI(MBB, MBBI, dl, TII.get(Xtensa::MOVSP), SP).addReg(TmpReg);
     }
 
+    // Store FP register in A8, because FP may be used to pass function
+    // arguments
+    if (STI.hasDensity()) {
+      BuildMI(MBB, MBBI, dl, TII.get(Xtensa::MOV_N), Xtensa::A8).addReg(FP);
+    } else {
+      BuildMI(MBB, MBBI, dl, TII.get(Xtensa::OR), Xtensa::A8)
+          .addReg(FP)
+          .addReg(FP);
+    }
+
     // if framepointer enabled, set it to point to the stack pointer.
     if (hasFP(MF)) {
       // Insert instruction "move $fp, $sp" at this location.
@@ -158,7 +168,15 @@ void XtensaFrameLowering::emitPrologue(MachineFunction &MF,
     if (StackSize == 0 && !MFI.adjustsStack())
       return;
 
-    // MachineLocation DstML, SrcML;
+    // Store FP register in A8, because FP may be used to pass function
+    // arguments
+    if (STI.hasDensity()) {
+      BuildMI(MBB, MBBI, dl, TII.get(Xtensa::MOV_N), Xtensa::A8).addReg(FP);
+    } else {
+      BuildMI(MBB, MBBI, dl, TII.get(Xtensa::OR), Xtensa::A8)
+          .addReg(FP)
+          .addReg(FP);
+    }
 
     // Adjust stack.
     TII.adjustStackPtr(SP, -StackSize, MBB, MBBI);

llvm/lib/Target/Xtensa/XtensaISelLowering.cpp

@@ -739,7 +739,17 @@ SDValue XtensaTargetLowering::LowerFormalArguments(
 
       // Transform the arguments stored on
       // physical registers into virtual ones
-      unsigned Reg = MF.addLiveIn(VA.getLocReg(), RC);
+      unsigned Reg = 0;
+      unsigned FrameReg = Subtarget.getRegisterInfo()->getFrameRegister(MF);
+
+      // Argument passed in FrameReg we save in A8 (in emitPrologue), 
+      // so load argument from A8
+      if (VA.getLocReg() == FrameReg) {
+        Reg = MF.addLiveIn(Xtensa::A8, RC);
+      } else {
+        Reg = MF.addLiveIn(VA.getLocReg(), RC);
+      }
+
       SDValue ArgValue = DAG.getCopyFromReg(Chain, DL, Reg, RegVT);
 
       // If this is an 8 or 16-bit value, it has been passed promoted
@@ -818,7 +828,16 @@ SDValue XtensaTargetLowering::LowerFormalArguments(
     // to the vararg save area.
     for (unsigned I = Idx; I < ArgRegs.size(); ++I, VaArgOffset += RegSize) {
       const unsigned Reg = RegInfo.createVirtualRegister(RC);
-      RegInfo.addLiveIn(ArgRegs[I], Reg);
+      unsigned FrameReg = Subtarget.getRegisterInfo()->getFrameRegister(MF);
+
+      // Argument passed in FrameReg we save in A8 (in emitPrologue),
+      // so load argument from A8
+      if (ArgRegs[I] == FrameReg) {
+        RegInfo.addLiveIn(Xtensa::A8, Reg);
+      } else {
+        RegInfo.addLiveIn(ArgRegs[I], Reg);
+      }
+
       SDValue ArgValue = DAG.getCopyFromReg(Chain, DL, Reg, RegTy);
       FI = MFI.CreateFixedObject(RegSize, VaArgOffset, true);
       SDValue PtrOff = DAG.getFrameIndex(FI, getPointerTy(DAG.getDataLayout()));