[RISCV] Don't emit save-restore call if function is a interrupt handler

[Jim]

Summary

It has to save all caller-saved registers before a call in the handler.
So don't emit a call that save/restore registers.

[simoncook]

This LGTM, I've left a note on a potential comment update, but otherwise looks good

llvm/lib/Target/RISCV/RISCVMachineFunctionInfo.h

63

Can you update this comment to put , or is an interrupt handler

[Jim]

Address comment

[luismarques]

Thanks, good catch. LGTM.

I wonder if this test should just go in the existing saverestore.ll test?

[Jim]

Address @luismarques's comment

[jrtc27]

llvm/test/CodeGen/RISCV/saverestore.ll

304

Inline the attribute

[Jim]

Address @jrtc27's comment.

llvm/lib/Target/RISCV/RISCVMachineFunctionInfo.h

int getMoveF64FrameIndex(MachineFunction &MF) {
     return MoveF64FrameIndex;
   }
 
   unsigned getLibCallStackSize() const { return LibCallStackSize; }
   void setLibCallStackSize(unsigned Size) { LibCallStackSize = Size; }
 
   bool useSaveRestoreLibCalls(const MachineFunction &MF) const {
     // We cannot use fixed locations for the callee saved spill slots if the
-    // function uses a varargs save area.
+    // function uses a varargs save area, or is an interrupt handler.
     return MF.getSubtarget<RISCVSubtarget>().enableSaveRestore() &&
-           VarArgsSaveSize == 0 && !MF.getFrameInfo().hasTailCall();
+           VarArgsSaveSize == 0 && !MF.getFrameInfo().hasTailCall() &&
+           !MF.getFunction().hasFnAttribute("interrupt");
   }
 
   uint64_t getRVVStackSize() const { return RVVStackSize; }
   void setRVVStackSize(uint64_t Size) { RVVStackSize = Size; }
 
   uint64_t getRVVPadding() const { return RVVPadding; }
   void setRVVPadding(uint64_t Padding) { RVVPadding = Padding; }
 
   unsigned getCalleeSavedStackSize() const { return CalleeSavedStackSize; }
   void setCalleeSavedStackSize(unsigned Size) { CalleeSavedStackSize = Size; }
 };
 
 } // end namespace llvm
 
 #endif // LLVM_LIB_TARGET_RISCV_RISCVMACHINEFUNCTIONINFO_H

llvm/test/CodeGen/RISCV/saverestore.ll

 ; RV64I-FP-SR:         addi sp, s0, -32
 ; RV64I-FP-SR:         tail __riscv_restore_2
   %sp = call i8* @llvm.stacksave()
   %addr = alloca i8, i32 %n
   call void @notdead(i8* %addr)
   call void @llvm.stackrestore(i8* %sp)
   ret void
 }
+
+; Check that functions with interrupt attribute do not use save/restore code
+
+declare i32 @foo(...)
+define void @interrupt() nounwind "interrupt"="user" {
+; RV32I-LABEL: interrupt:
+; RV32I-NOT:     call t0, __riscv_save
+; RV32I-NOT:     tail __riscv_restore
+;
+; RV64I-LABEL: interrupt:
+; RV64I-NOT:     call t0, __riscv_save
+; RV64I-NOT:     tail __riscv_restore
+;
+; RV32I-SR-LABEL: interrupt:
+; RV32I-SR-NOT:     call t0, __riscv_save
+; RV32I-SR-NOT:     tail __riscv_restore
+;
+; RV64I-SR-LABEL: interrupt:
+; RV64I-SR-NOT:     call t0, __riscv_save
+; RV64I-SR-NOT:     tail __riscv_restore
+;
+; RV32I-FP-SR-LABEL: interrupt:
+; RV32I-FP-SR-NOT:     call t0, __riscv_save
+; RV32I-FP-SR-NOT:     tail __riscv_restore
+;
+; RV64I-FP-SR-LABEL: interrupt:
+; RV64I-FP-SR-NOT:     call t0, __riscv_save
+; RV64I-FP-SR-NOT:     tail __riscv_restore
+  %call = call i32 bitcast (i32 (...)* @foo to i32 ()*)()
+  ret void
+}