Index: llvm/trunk/lib/Target/RISCV/RISCVISelDAGToDAG.cpp
===================================================================
--- llvm/trunk/lib/Target/RISCV/RISCVISelDAGToDAG.cpp
+++ llvm/trunk/lib/Target/RISCV/RISCVISelDAGToDAG.cpp
@@ -11,9 +11,10 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "RISCV.h"
 #include "MCTargetDesc/RISCVMCTargetDesc.h"
+#include "RISCV.h"
 #include "RISCVTargetMachine.h"
+#include "Utils/RISCVMatInt.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/SelectionDAGISel.h"
 #include "llvm/Support/Debug.h"
@@ -63,6 +64,27 @@
   doPeepholeLoadStoreADDI();
 }
 
+static SDNode *selectImm(SelectionDAG *CurDAG, const SDLoc &DL, int64_t Imm,
+                         MVT XLenVT) {
+  RISCVMatInt::InstSeq Seq;
+  RISCVMatInt::generateInstSeq(Imm, XLenVT == MVT::i64, Seq);
+
+  SDNode *Result;
+  SDValue SrcReg = CurDAG->getRegister(RISCV::X0, XLenVT);
+  for (RISCVMatInt::Inst &Inst : Seq) {
+    SDValue SDImm = CurDAG->getTargetConstant(Inst.Imm, DL, XLenVT);
+    if (Inst.Opc == RISCV::LUI)
+      Result = CurDAG->getMachineNode(RISCV::LUI, DL, XLenVT, SDImm);
+    else
+      Result = CurDAG->getMachineNode(Inst.Opc, DL, XLenVT, SrcReg, SDImm);
+
+    // Only the first instruction has X0 as its source.
+    SrcReg = SDValue(Result, 0);
+  }
+
+  return Result;
+}
+
 void RISCVDAGToDAGISel::Select(SDNode *Node) {
   // If we have a custom node, we have already selected.
   if (Node->isMachineOpcode()) {
@@ -87,6 +109,11 @@
       ReplaceNode(Node, New.getNode());
       return;
     }
+    int64_t Imm = ConstNode->getSExtValue();
+    if (XLenVT == MVT::i64) {
+      ReplaceNode(Node, selectImm(CurDAG, SDLoc(Node), Imm, XLenVT));
+      return;
+    }
     break;
   }
   case ISD::FrameIndex: {
Index: llvm/trunk/test/CodeGen/RISCV/imm.ll
===================================================================
--- llvm/trunk/test/CodeGen/RISCV/imm.ll
+++ llvm/trunk/test/CodeGen/RISCV/imm.ll
@@ -1,63 +1,260 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
 ; RUN: llc -mtriple=riscv32 -verify-machineinstrs < %s \
 ; RUN:   | FileCheck %s -check-prefix=RV32I
+; RUN: llc -mtriple=riscv64 -verify-machineinstrs < %s \
+; RUN:   | FileCheck %s -check-prefix=RV64I
 
 ; Materializing constants
 
-define i32 @zero() nounwind {
+; TODO: It would be preferable if anyext constant returns were sign rather
+; than zero extended. See PR39092. For now, mark returns as explicitly signext
+; (this matches what Clang would generate for equivalent C/C++ anyway).
+
+define signext i32 @zero() nounwind {
 ; RV32I-LABEL: zero:
 ; RV32I:       # %bb.0:
 ; RV32I-NEXT:    mv a0, zero
 ; RV32I-NEXT:    ret
+;
+; RV64I-LABEL: zero:
+; RV64I:       # %bb.0:
+; RV64I-NEXT:    mv a0, zero
+; RV64I-NEXT:    ret
   ret i32 0
 }
 
-define i32 @pos_small() nounwind {
+define signext i32 @pos_small() nounwind {
 ; RV32I-LABEL: pos_small:
 ; RV32I:       # %bb.0:
 ; RV32I-NEXT:    addi a0, zero, 2047
 ; RV32I-NEXT:    ret
+;
+; RV64I-LABEL: pos_small:
+; RV64I:       # %bb.0:
+; RV64I-NEXT:    addi a0, zero, 2047
+; RV64I-NEXT:    ret
   ret i32 2047
 }
 
-define i32 @neg_small() nounwind {
+define signext i32 @neg_small() nounwind {
 ; RV32I-LABEL: neg_small:
 ; RV32I:       # %bb.0:
 ; RV32I-NEXT:    addi a0, zero, -2048
 ; RV32I-NEXT:    ret
+;
+; RV64I-LABEL: neg_small:
+; RV64I:       # %bb.0:
+; RV64I-NEXT:    addi a0, zero, -2048
+; RV64I-NEXT:    ret
   ret i32 -2048
 }
 
-define i32 @pos_i32() nounwind {
+define signext i32 @pos_i32() nounwind {
 ; RV32I-LABEL: pos_i32:
 ; RV32I:       # %bb.0:
 ; RV32I-NEXT:    lui a0, 423811
 ; RV32I-NEXT:    addi a0, a0, -1297
 ; RV32I-NEXT:    ret
+;
+; RV64I-LABEL: pos_i32:
+; RV64I:       # %bb.0:
+; RV64I-NEXT:    lui a0, 423811
+; RV64I-NEXT:    addiw a0, a0, -1297
+; RV64I-NEXT:    ret
   ret i32 1735928559
 }
 
-define i32 @neg_i32() nounwind {
+define signext i32 @neg_i32() nounwind {
 ; RV32I-LABEL: neg_i32:
 ; RV32I:       # %bb.0:
 ; RV32I-NEXT:    lui a0, 912092
 ; RV32I-NEXT:    addi a0, a0, -273
 ; RV32I-NEXT:    ret
+;
+; RV64I-LABEL: neg_i32:
+; RV64I:       # %bb.0:
+; RV64I-NEXT:    lui a0, 912092
+; RV64I-NEXT:    addiw a0, a0, -273
+; RV64I-NEXT:    ret
   ret i32 -559038737
 }
 
-define i32 @pos_i32_hi20_only() nounwind {
+define signext i32 @pos_i32_hi20_only() nounwind {
 ; RV32I-LABEL: pos_i32_hi20_only:
 ; RV32I:       # %bb.0:
 ; RV32I-NEXT:    lui a0, 16
 ; RV32I-NEXT:    ret
+;
+; RV64I-LABEL: pos_i32_hi20_only:
+; RV64I:       # %bb.0:
+; RV64I-NEXT:    lui a0, 16
+; RV64I-NEXT:    ret
   ret i32 65536
 }
 
-define i32 @neg_i32_hi20_only() nounwind {
+define signext i32 @neg_i32_hi20_only() nounwind {
 ; RV32I-LABEL: neg_i32_hi20_only:
 ; RV32I:       # %bb.0:
 ; RV32I-NEXT:    lui a0, 1048560
 ; RV32I-NEXT:    ret
+;
+; RV64I-LABEL: neg_i32_hi20_only:
+; RV64I:       # %bb.0:
+; RV64I-NEXT:    lui a0, 1048560
+; RV64I-NEXT:    ret
   ret i32 -65536
 }
+
+define i64 @imm64_1() nounwind {
+; RV32I-LABEL: imm64_1:
+; RV32I:       # %bb.0:
+; RV32I-NEXT:    lui a0, 524288
+; RV32I-NEXT:    mv a1, zero
+; RV32I-NEXT:    ret
+;
+; RV64I-LABEL: imm64_1:
+; RV64I:       # %bb.0:
+; RV64I-NEXT:    addi a0, zero, 1
+; RV64I-NEXT:    slli a0, a0, 31
+; RV64I-NEXT:    ret
+  ret i64 2147483648
+}
+
+; TODO: This and similar constants with all 0s in the upper bits and all 1s in
+; the lower bits could be lowered to addi a0, zero, -1 followed by a logical
+; right shift.
+define i64 @imm64_2() nounwind {
+; RV32I-LABEL: imm64_2:
+; RV32I:       # %bb.0:
+; RV32I-NEXT:    addi a0, zero, -1
+; RV32I-NEXT:    mv a1, zero
+; RV32I-NEXT:    ret
+;
+; RV64I-LABEL: imm64_2:
+; RV64I:       # %bb.0:
+; RV64I-NEXT:    addi a0, zero, 1
+; RV64I-NEXT:    slli a0, a0, 32
+; RV64I-NEXT:    addi a0, a0, -1
+; RV64I-NEXT:    ret
+  ret i64 4294967295
+}
+
+define i64 @imm64_3() nounwind {
+; RV32I-LABEL: imm64_3:
+; RV32I:       # %bb.0:
+; RV32I-NEXT:    addi a1, zero, 1
+; RV32I-NEXT:    mv a0, zero
+; RV32I-NEXT:    ret
+;
+; RV64I-LABEL: imm64_3:
+; RV64I:       # %bb.0:
+; RV64I-NEXT:    addi a0, zero, 1
+; RV64I-NEXT:    slli a0, a0, 32
+; RV64I-NEXT:    ret
+  ret i64 4294967296
+}
+
+define i64 @imm64_4() nounwind {
+; RV32I-LABEL: imm64_4:
+; RV32I:       # %bb.0:
+; RV32I-NEXT:    lui a1, 524288
+; RV32I-NEXT:    mv a0, zero
+; RV32I-NEXT:    ret
+;
+; RV64I-LABEL: imm64_4:
+; RV64I:       # %bb.0:
+; RV64I-NEXT:    addi a0, zero, -1
+; RV64I-NEXT:    slli a0, a0, 63
+; RV64I-NEXT:    ret
+  ret i64 9223372036854775808
+}
+
+define i64 @imm64_5() nounwind {
+; RV32I-LABEL: imm64_5:
+; RV32I:       # %bb.0:
+; RV32I-NEXT:    lui a1, 524288
+; RV32I-NEXT:    mv a0, zero
+; RV32I-NEXT:    ret
+;
+; RV64I-LABEL: imm64_5:
+; RV64I:       # %bb.0:
+; RV64I-NEXT:    addi a0, zero, -1
+; RV64I-NEXT:    slli a0, a0, 63
+; RV64I-NEXT:    ret
+  ret i64 -9223372036854775808
+}
+
+define i64 @imm64_6() nounwind {
+; RV32I-LABEL: imm64_6:
+; RV32I:       # %bb.0:
+; RV32I-NEXT:    lui a0, 74565
+; RV32I-NEXT:    addi a1, a0, 1656
+; RV32I-NEXT:    mv a0, zero
+; RV32I-NEXT:    ret
+;
+; RV64I-LABEL: imm64_6:
+; RV64I:       # %bb.0:
+; RV64I-NEXT:    lui a0, 9321
+; RV64I-NEXT:    addiw a0, a0, -1329
+; RV64I-NEXT:    slli a0, a0, 35
+; RV64I-NEXT:    ret
+  ret i64 1311768464867721216
+}
+
+define i64 @imm64_7() nounwind {
+; RV32I-LABEL: imm64_7:
+; RV32I:       # %bb.0:
+; RV32I-NEXT:    lui a0, 45056
+; RV32I-NEXT:    addi a0, a0, 15
+; RV32I-NEXT:    lui a1, 458752
+; RV32I-NEXT:    ret
+;
+; RV64I-LABEL: imm64_7:
+; RV64I:       # %bb.0:
+; RV64I-NEXT:    addi a0, zero, 7
+; RV64I-NEXT:    slli a0, a0, 36
+; RV64I-NEXT:    addi a0, a0, 11
+; RV64I-NEXT:    slli a0, a0, 24
+; RV64I-NEXT:    addi a0, a0, 15
+; RV64I-NEXT:    ret
+  ret i64 8070450532432478223
+}
+
+; TODO: it can be preferable to put constants that are expensive to materialise
+; into the constant pool, especially for -Os.
+define i64 @imm64_8() nounwind {
+; RV32I-LABEL: imm64_8:
+; RV32I:       # %bb.0:
+; RV32I-NEXT:    lui a0, 633806
+; RV32I-NEXT:    addi a0, a0, -272
+; RV32I-NEXT:    lui a1, 74565
+; RV32I-NEXT:    addi a1, a1, 1656
+; RV32I-NEXT:    ret
+;
+; RV64I-LABEL: imm64_8:
+; RV64I:       # %bb.0:
+; RV64I-NEXT:    lui a0, 583
+; RV64I-NEXT:    addiw a0, a0, -1875
+; RV64I-NEXT:    slli a0, a0, 14
+; RV64I-NEXT:    addi a0, a0, -947
+; RV64I-NEXT:    slli a0, a0, 12
+; RV64I-NEXT:    addi a0, a0, 1511
+; RV64I-NEXT:    slli a0, a0, 13
+; RV64I-NEXT:    addi a0, a0, -272
+; RV64I-NEXT:    ret
+  ret i64 1311768467463790320
+}
+
+define i64 @imm64_9() nounwind {
+; RV32I-LABEL: imm64_9:
+; RV32I:       # %bb.0:
+; RV32I-NEXT:    addi a0, zero, -1
+; RV32I-NEXT:    mv a1, a0
+; RV32I-NEXT:    ret
+;
+; RV64I-LABEL: imm64_9:
+; RV64I:       # %bb.0:
+; RV64I-NEXT:    addi a0, zero, -1
+; RV64I-NEXT:    ret
+  ret i64 -1
+}