[PATCH] D62686: [RISCV] Add support for save/restore of callee-saved registers via libcalls

[Shiva Chen via Phabricator via llvm-commits]

shiva0217 added inline comments.


================
Comment at: llvm/lib/Target/RISCV/RISCVFrameLowering.cpp:289
   unsigned CFIIndex = MF.addFrameInst(
       MCCFIInstruction::createDefCfaOffset(nullptr, -StackSize));
   BuildMI(MBB, MBBI, DL, TII->get(TargetOpcode::CFI_INSTRUCTION))
----------------
Should the -StackSize be -RealStackSize?


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Comment at: llvm/lib/Target/RISCV/RISCVFrameLowering.cpp:667
+        .addExternalSymbol(SpillLibCall, RISCVII::MO_CALL)
+        .setMIFlag(MachineInstr::FrameSetup);
+
----------------
There is a case may trigger an assertion when compile with -O3 -g -msave-restore if the libcall has FrameSetup flag.
  int main(int a, char* argv[]) {
    exit(0);
    return 0;
  }


================
Comment at: llvm/lib/Target/RISCV/RISCVFrameLowering.cpp:668
+        .setMIFlag(MachineInstr::FrameSetup);
+
+    // Add registers spilled in libcall as liveins.
----------------
GCC will generate stack adjustment and GPR callee saved CFIs for the save libcalls. Should we do the same?


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Comment at: llvm/lib/Target/RISCV/RISCVRegisterInfo.h:40
 
+  bool hasReservedSpillSlot(const MachineFunction &MF, unsigned Reg,
+                            int &FrameIdx) const override;
----------------
An alternative of defining hasReservedSpillSlot could be set SaveRegs for the registers will be pushed by the libcalls in determineCalleeSaves. So the StackSize calculation will take the callee saved registers will be pushed by the libcalls into account.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D62686/new/

https://reviews.llvm.org/D62686