[RISCV] Mark FREM as Expand

[luismarques]

Summary

Mark the FREM SelectionDAG node as Expand, which is necessary in order to support the frem IR instruction on RISC-V. This is expanded into a library call. Adds the corresponding test. Previously, this would have triggered an assertion at instruction selection time.

[rogfer01]

LGTM.

Thanks Luis. I merged your earlier change D54034 into my downstream compiler just to find that frem was missing (triggered by a downstream test).

The fix I did is exactly this change (modulo the test).

[asb]

Could you please a double-frem.ll test as well?

[luismarques]

Adds double-frem.ll test.

lib/Target/RISCV/RISCVISelLowering.cpp

RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
   ISD::CondCode FPCCToExtend[] = {
       ISD::SETOGT, ISD::SETOGE, ISD::SETONE, ISD::SETO,   ISD::SETUEQ,
       ISD::SETUGT, ISD::SETUGE, ISD::SETULT, ISD::SETULE, ISD::SETUNE,
       ISD::SETGT,  ISD::SETGE,  ISD::SETNE};
 
   // TODO: add proper support for the various FMA variants
   // (FMADD.S, FMSUB.S, FNMSUB.S, FNMADD.S).
   ISD::NodeType FPOpToExtend[] = {
-      ISD::FSIN, ISD::FCOS, ISD::FSINCOS, ISD::FPOW, ISD::FMA};
+      ISD::FSIN, ISD::FCOS, ISD::FSINCOS, ISD::FPOW, ISD::FMA, ISD::FREM};
 
   if (Subtarget.hasStdExtF()) {
     setOperationAction(ISD::FMINNUM, MVT::f32, Legal);
     setOperationAction(ISD::FMAXNUM, MVT::f32, Legal);
     for (auto CC : FPCCToExtend)
       setCondCodeAction(CC, MVT::f32, Expand);
     setOperationAction(ISD::SELECT_CC, MVT::f32, Expand);
     setOperationAction(ISD::SELECT, MVT::f32, Custom);

test/CodeGen/RISCV/float-frem.ll

+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=riscv32 -mattr=+f -verify-machineinstrs < %s \
+; RUN:   | FileCheck -check-prefix=RV32IF %s
+
+define float @frem_f32(float %a, float %b) nounwind {
+; RV32IF-LABEL: frem_f32:
+; RV32IF:       # %bb.0:
+; RV32IF-NEXT:    addi sp, sp, -16
+; RV32IF-NEXT:    sw ra, 12(sp)
+; RV32IF-NEXT:    call fmodf
+; RV32IF-NEXT:    lw ra, 12(sp)
+; RV32IF-NEXT:    addi sp, sp, 16
+; RV32IF-NEXT:    ret
+  %1 = frem float %a, %b
+  ret float %1
+}