[RISCV][FPEnv] Lowering of fpmode intrinsics (llvm#148569)

The change implements custom lowering of `get_fpmode`, `set_fpmode` and
`reset_fpmode` for RISCV target. The implementation is aligned with the
functions `fegetmode` and `fesetmode` in GLIBC.

Author: spavloff

llvm/lib/Target/RISCV/MCTargetDesc/RISCVBaseInfo.h

@@ -494,6 +494,17 @@ inline static bool isValidRoundingMode(unsigned Mode) {
 }
 } // namespace RISCVVXRndMode
 
+namespace RISCVExceptFlags {
+enum ExceptionFlag {
+  NX = 0x01, // Inexact
+  UF = 0x02, // Underflow
+  OF = 0x04, // Overflow
+  DZ = 0x08, // Divide by zero
+  NV = 0x10, // Invalid operation
+  ALL = 0x1F // Mask for all accrued exception flags
+};
+}
+
 //===----------------------------------------------------------------------===//
 // Floating-point Immediates
 //

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -655,6 +655,9 @@ RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
     setOperationAction(ISD::GET_FPENV, XLenVT, Custom);
     setOperationAction(ISD::SET_FPENV, XLenVT, Custom);
     setOperationAction(ISD::RESET_FPENV, MVT::Other, Custom);
+    setOperationAction(ISD::GET_FPMODE, XLenVT, Custom);
+    setOperationAction(ISD::SET_FPMODE, XLenVT, Custom);
+    setOperationAction(ISD::RESET_FPMODE, MVT::Other, Custom);
   }
 
   setOperationAction({ISD::GlobalAddress, ISD::BlockAddress, ISD::ConstantPool,
@@ -8225,6 +8228,12 @@ SDValue RISCVTargetLowering::LowerOperation(SDValue Op,
     return lowerSET_FPENV(Op, DAG);
   case ISD::RESET_FPENV:
     return lowerRESET_FPENV(Op, DAG);
+  case ISD::GET_FPMODE:
+    return lowerGET_FPMODE(Op, DAG);
+  case ISD::SET_FPMODE:
+    return lowerSET_FPMODE(Op, DAG);
+  case ISD::RESET_FPMODE:
+    return lowerRESET_FPMODE(Op, DAG);
   case ISD::EH_DWARF_CFA:
     return lowerEH_DWARF_CFA(Op, DAG);
   case ISD::VP_MERGE:
@@ -14002,6 +14011,54 @@ SDValue RISCVTargetLowering::lowerRESET_FPENV(SDValue Op,
                      EnvValue);
 }
 
+const uint64_t ModeMask64 = ~RISCVExceptFlags::ALL;
+const uint32_t ModeMask32 = ~RISCVExceptFlags::ALL;
+
+SDValue RISCVTargetLowering::lowerGET_FPMODE(SDValue Op,
+                                             SelectionDAG &DAG) const {
+  const MVT XLenVT = Subtarget.getXLenVT();
+  const uint64_t ModeMaskValue = Subtarget.is64Bit() ? ModeMask64 : ModeMask32;
+  SDLoc DL(Op);
+  SDValue Chain = Op->getOperand(0);
+  SDValue SysRegNo = DAG.getTargetConstant(RISCVSysReg::fcsr, DL, XLenVT);
+  SDValue ModeMask = DAG.getConstant(ModeMaskValue, DL, XLenVT);
+  SDVTList VTs = DAG.getVTList(XLenVT, MVT::Other);
+  SDValue Result = DAG.getNode(RISCVISD::READ_CSR, DL, VTs, Chain, SysRegNo);
+  Chain = Result.getValue(1);
+  return DAG.getMergeValues({Result, Chain}, DL);
+}
+
+SDValue RISCVTargetLowering::lowerSET_FPMODE(SDValue Op,
+                                             SelectionDAG &DAG) const {
+  const MVT XLenVT = Subtarget.getXLenVT();
+  const uint64_t ModeMaskValue = Subtarget.is64Bit() ? ModeMask64 : ModeMask32;
+  SDLoc DL(Op);
+  SDValue Chain = Op->getOperand(0);
+  SDValue EnvValue = Op->getOperand(1);
+  SDValue SysRegNo = DAG.getTargetConstant(RISCVSysReg::fcsr, DL, XLenVT);
+  SDValue ModeMask = DAG.getConstant(ModeMaskValue, DL, XLenVT);
+
+  EnvValue = DAG.getNode(ISD::ZERO_EXTEND, DL, XLenVT, EnvValue);
+  EnvValue = DAG.getNode(ISD::AND, DL, XLenVT, EnvValue, ModeMask);
+  Chain = DAG.getNode(RISCVISD::CLEAR_CSR, DL, MVT::Other, Chain, SysRegNo,
+                      ModeMask);
+  return DAG.getNode(RISCVISD::SET_CSR, DL, MVT::Other, Chain, SysRegNo,
+                     EnvValue);
+}
+
+SDValue RISCVTargetLowering::lowerRESET_FPMODE(SDValue Op,
+                                               SelectionDAG &DAG) const {
+  const MVT XLenVT = Subtarget.getXLenVT();
+  const uint64_t ModeMaskValue = Subtarget.is64Bit() ? ModeMask64 : ModeMask32;
+  SDLoc DL(Op);
+  SDValue Chain = Op->getOperand(0);
+  SDValue SysRegNo = DAG.getTargetConstant(RISCVSysReg::fcsr, DL, XLenVT);
+  SDValue ModeMask = DAG.getConstant(ModeMaskValue, DL, XLenVT);
+
+  return DAG.getNode(RISCVISD::CLEAR_CSR, DL, MVT::Other, Chain, SysRegNo,
+                     ModeMask);
+}
+
 SDValue RISCVTargetLowering::lowerEH_DWARF_CFA(SDValue Op,
                                                SelectionDAG &DAG) const {
   MachineFunction &MF = DAG.getMachineFunction();

llvm/lib/Target/RISCV/RISCVISelLowering.h

@@ -563,6 +563,9 @@ class RISCVTargetLowering : public TargetLowering {
   SDValue lowerGET_FPENV(SDValue Op, SelectionDAG &DAG) const;
   SDValue lowerSET_FPENV(SDValue Op, SelectionDAG &DAG) const;
   SDValue lowerRESET_FPENV(SDValue Op, SelectionDAG &DAG) const;
+  SDValue lowerGET_FPMODE(SDValue Op, SelectionDAG &DAG) const;
+  SDValue lowerSET_FPMODE(SDValue Op, SelectionDAG &DAG) const;
+  SDValue lowerRESET_FPMODE(SDValue Op, SelectionDAG &DAG) const;
 
   SDValue lowerEH_DWARF_CFA(SDValue Op, SelectionDAG &DAG) const;
   SDValue lowerCTLZ_CTTZ_ZERO_UNDEF(SDValue Op, SelectionDAG &DAG) const;

llvm/lib/Target/RISCV/RISCVInstrInfo.td

@@ -120,6 +120,20 @@ def riscv_swap_csr  : RVSDNode<"SWAP_CSR",
                                                     SDTCisInt<2>]>,
                                [SDNPHasChain]>;
 
+// Clear bits of CSR. The first operand is the address of the required CSR,
+// the second is the bitmask of cleared bits.
+def riscv_clear_csr  : RVSDNode<"CLEAR_CSR",
+                               SDTypeProfile<0, 2, [SDTCisInt<0>,
+                                                    SDTCisInt<1>]>,
+                               [SDNPHasChain]>;
+
+// Set bits of CSR. The first operand is the address of the required CSR,
+// the second is the bitmask of bits to set.
+def riscv_set_csr  : RVSDNode<"SET_CSR",
+                               SDTypeProfile<0, 2, [SDTCisInt<0>,
+                                                    SDTCisInt<1>]>,
+                               [SDNPHasChain]>;
+
 // A read of the 64-bit counter CSR on a 32-bit target (returns (Lo, Hi)).
 // It takes a chain operand and another two target constant operands (the
 // CSR numbers of the low and high parts of the counter).
@@ -2038,6 +2052,42 @@ class SwapSysRegImm<SysReg SR, list<Register> Regs>
   let Defs = Regs;
 }
 
+class ClearSysReg<SysReg SR, list<Register> Regs>
+  : Pseudo<(outs), (ins GPR:$val),
+           [(riscv_clear_csr (XLenVT SR.Encoding), (XLenVT GPR:$val))]>,
+    PseudoInstExpansion<(CSRRC X0, SR.Encoding, GPR:$val)> {
+  let hasSideEffects = 0;
+  let Uses = Regs;
+  let Defs = Regs;
+}
+
+class ClearSysRegImm<SysReg SR, list<Register> Regs>
+  : Pseudo<(outs), (ins uimm5:$val),
+           [(riscv_clear_csr (XLenVT SR.Encoding), uimm5:$val)]>,
+    PseudoInstExpansion<(CSRRCI X0, SR.Encoding, uimm5:$val)> {
+  let hasSideEffects = 0;
+  let Uses = Regs;
+  let Defs = Regs;
+}
+
+class SetSysReg<SysReg SR, list<Register> Regs>
+  : Pseudo<(outs), (ins GPR:$val),
+           [(riscv_set_csr (XLenVT SR.Encoding), (XLenVT GPR:$val))]>,
+    PseudoInstExpansion<(CSRRS X0, SR.Encoding, GPR:$val)> {
+  let hasSideEffects = 0;
+  let Uses = Regs;
+  let Defs = Regs;
+}
+
+class SetSysRegImm<SysReg SR, list<Register> Regs>
+  : Pseudo<(outs), (ins uimm5:$val),
+           [(riscv_set_csr (XLenVT SR.Encoding), uimm5:$val)]>,
+    PseudoInstExpansion<(CSRRSI X0, SR.Encoding, uimm5:$val)> {
+  let hasSideEffects = 0;
+  let Uses = Regs;
+  let Defs = Regs;
+}
+
 def ReadFRM : ReadSysReg<SysRegFRM, [FRM]>;
 let hasPostISelHook = 1 in {
 def WriteFRM : WriteSysReg<SysRegFRM, [FRM]>;
@@ -2056,6 +2106,10 @@ let hasPostISelHook = 1 in {
 def ReadFCSR : ReadSysReg<SysRegFCSR, [FRM, FFLAGS]>;
 def WriteFCSR : WriteSysReg<SysRegFCSR, [FRM, FFLAGS]>;
 def WriteFCSRImm : WriteSysRegImm<SysRegFCSR, [FRM, FFLAGS]>;
+def ClearFCSR : ClearSysReg<SysRegFCSR, [FRM, FFLAGS]>;
+def ClearFCSRImm : ClearSysRegImm<SysRegFCSR, [FRM, FFLAGS]>;
+def SetFCSR : SetSysReg<SysRegFCSR, [FRM, FFLAGS]>;
+def SetFCSRImm : SetSysRegImm<SysRegFCSR, [FRM, FFLAGS]>;
 }
 
 /// Other pseudo-instructions

llvm/test/CodeGen/RISCV/fpenv-xlen.ll

@@ -35,3 +35,37 @@ entry:
   call void @llvm.reset.fpenv()
   ret void
 }
+
+define iXLen @func_get_fpmode() {
+; CHECK-LABEL: func_get_fpmode:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    frcsr a0
+; CHECK-NEXT:    ret
+entry:
+  %fpenv = call iXLen @llvm.get.fpmode.iXLen()
+  ret iXLen %fpenv
+}
+
+define void @func_set_fpmode(iXLen %fpmode) {
+; CHECK-LABEL: func_set_fpmode:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    li    a1, -32
+; CHECK-NEXT:    csrc  fcsr, a1
+; CHECK-NEXT:    andi  a0, a0, -32
+; CHECK-NEXT:    csrs  fcsr, a0
+; CHECK-NEXT:    ret
+entry:
+  call void @llvm.set.fpmode.iXLen(iXLen %fpmode)
+  ret void
+}
+
+define void @func_reset_fpmode() {
+; CHECK-LABEL: func_reset_fpmode:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    li   a0, -32
+; CHECK-NEXT:    csrc fcsr, a0
+; CHECK-NEXT:    ret
+entry:
+  call void @llvm.reset.fpmode()
+  ret void
+}