[RISCV] Fold (xor (sllw 1, x), -1) -> (rolw ~1, x).

[craig.topper]

Summary

There's an existing generic combine that does this for legal types.
This patch adds a RISCV specific combine for W instructions.

[luismarques]

LGTM.

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

static SDValue performORCombine(SDNode *N, SelectionDAG &DAG,
   }
 
   // fold (or (select cond, 0, y), x) ->
   //      (select cond, x, (or x, y))
   return combineSelectAndUseCommutative(N, DAG, /*AllOnes*/ false);
 }
 
 static SDValue performXORCombine(SDNode *N, SelectionDAG &DAG) {
+  SDValue N0 = N->getOperand(0);
+  SDValue N1 = N->getOperand(1);
+
+  // fold (xor (sllw 1, x), -1) -> (rolw ~1, x)
+  // NOTE: Assumes ROL being legal means ROLW is legal.
+  const TargetLowering &TLI = DAG.getTargetLoweringInfo();
+  if (N0.getOpcode() == RISCVISD::SLLW &&
+      isAllOnesConstant(N1) && isOneConstant(N0.getOperand(0)) &&
+      TLI.isOperationLegal(ISD::ROTL, MVT::i64)) {
+    SDLoc DL(N);
+    return DAG.getNode(RISCVISD::ROLW, DL, MVT::i64,
+                       DAG.getConstant(~1, DL, MVT::i64), N0.getOperand(1));
+  }
+
   // fold (xor (select cond, 0, y), x) ->
   //      (select cond, x, (xor x, y))
   return combineSelectAndUseCommutative(N, DAG, /*AllOnes*/ false);
 }
 
 static SDValue
 performSIGN_EXTEND_INREGCombine(SDNode *N, SelectionDAG &DAG,
                                 const RISCVSubtarget &Subtarget) {

llvm/test/CodeGen/RISCV/rv32zbb-zbp-zbkb.ll

 ; RV32ZBB-ZBP-ZBKB-NEXT:    slli a1, a1, 1
 ; RV32ZBB-ZBP-ZBKB-NEXT:    or a1, a1, a0
 ; RV32ZBB-ZBP-ZBKB-NEXT:    mv a0, a2
 ; RV32ZBB-ZBP-ZBKB-NEXT:    ret
   %1 = tail call i64 @llvm.fshr.i64(i64 %a, i64 %a, i64 63)
   ret i64 %1
 }
 
+define i32 @not_shl_one_i32(i32 %x) {
+; RV32I-LABEL: not_shl_one_i32:
+; RV32I:       # %bb.0:
+; RV32I-NEXT:    li a1, 1
+; RV32I-NEXT:    sll a0, a1, a0
+; RV32I-NEXT:    not a0, a0
+; RV32I-NEXT:    ret
+;
+; RV32ZBB-ZBP-ZBKB-LABEL: not_shl_one_i32:
+; RV32ZBB-ZBP-ZBKB:       # %bb.0:
+; RV32ZBB-ZBP-ZBKB-NEXT:    li a1, -2
+; RV32ZBB-ZBP-ZBKB-NEXT:    rol a0, a1, a0
+; RV32ZBB-ZBP-ZBKB-NEXT:    ret
+  %1 = shl i32 1, %x
+  %2 = xor i32 %1, -1
+  ret i32 %2
+}
+
+define i64 @not_shl_one_i64(i64 %x) {
+; RV32I-LABEL: not_shl_one_i64:
+; RV32I:       # %bb.0:
+; RV32I-NEXT:    addi a3, a0, -32
+; RV32I-NEXT:    li a2, 1
+; RV32I-NEXT:    li a1, -1
+; RV32I-NEXT:    bltz a3, .LBB15_2
+; RV32I-NEXT:  # %bb.1:
+; RV32I-NEXT:    sll a0, a2, a3
+; RV32I-NEXT:    not a1, a0
+; RV32I-NEXT:    li a0, -1
+; RV32I-NEXT:    ret
+; RV32I-NEXT:  .LBB15_2:
+; RV32I-NEXT:    sll a0, a2, a0
+; RV32I-NEXT:    not a0, a0
+; RV32I-NEXT:    ret
+;
+; RV32ZBB-ZBP-ZBKB-LABEL: not_shl_one_i64:
+; RV32ZBB-ZBP-ZBKB:       # %bb.0:
+; RV32ZBB-ZBP-ZBKB-NEXT:    addi a3, a0, -32
+; RV32ZBB-ZBP-ZBKB-NEXT:    li a2, -2
+; RV32ZBB-ZBP-ZBKB-NEXT:    li a1, -1
+; RV32ZBB-ZBP-ZBKB-NEXT:    bltz a3, .LBB15_2
+; RV32ZBB-ZBP-ZBKB-NEXT:  # %bb.1:
+; RV32ZBB-ZBP-ZBKB-NEXT:    rol a1, a2, a3
+; RV32ZBB-ZBP-ZBKB-NEXT:    li a0, -1
+; RV32ZBB-ZBP-ZBKB-NEXT:    ret
+; RV32ZBB-ZBP-ZBKB-NEXT:  .LBB15_2:
+; RV32ZBB-ZBP-ZBKB-NEXT:    rol a0, a2, a0
+; RV32ZBB-ZBP-ZBKB-NEXT:    ret
+  %1 = shl i64 1, %x
+  %2 = xor i64 %1, -1
+  ret i64 %2
+}
+
 define i8 @srli_i8(i8 %a) nounwind {
 ; RV32I-LABEL: srli_i8:
 ; RV32I:       # %bb.0:
 ; RV32I-NEXT:    slli a0, a0, 24
 ; RV32I-NEXT:    srli a0, a0, 30
 ; RV32I-NEXT:    ret
 ;
 ; RV32ZBB-ZBP-ZBKB-LABEL: srli_i8:

llvm/test/CodeGen/RISCV/rv64zbb-zbp-zbkb.ll

 ; RV64ZBB-ZBP-ZBKB-LABEL: rori_i64_fshr:
 ; RV64ZBB-ZBP-ZBKB:       # %bb.0:
 ; RV64ZBB-ZBP-ZBKB-NEXT:    rori a0, a0, 63
 ; RV64ZBB-ZBP-ZBKB-NEXT:    ret
   %1 = tail call i64 @llvm.fshr.i64(i64 %a, i64 %a, i64 63)
   ret i64 %1
 }
 
+define signext i32 @not_shl_one_i32(i32 signext %x) {
+; RV64I-LABEL: not_shl_one_i32:
+; RV64I:       # %bb.0:
+; RV64I-NEXT:    li a1, 1
+; RV64I-NEXT:    sllw a0, a1, a0
+; RV64I-NEXT:    not a0, a0
+; RV64I-NEXT:    ret
+;
+; RV64ZBB-ZBP-ZBKB-LABEL: not_shl_one_i32:
+; RV64ZBB-ZBP-ZBKB:       # %bb.0:
+; RV64ZBB-ZBP-ZBKB-NEXT:    li a1, -2
+; RV64ZBB-ZBP-ZBKB-NEXT:    rolw a0, a1, a0
+; RV64ZBB-ZBP-ZBKB-NEXT:    ret
+  %1 = shl i32 1, %x
+  %2 = xor i32 %1, -1
+  ret i32 %2
+}
+
+define i64 @not_shl_one_i64(i64 %x) {
+; RV64I-LABEL: not_shl_one_i64:
+; RV64I:       # %bb.0:
+; RV64I-NEXT:    li a1, 1
+; RV64I-NEXT:    sll a0, a1, a0
+; RV64I-NEXT:    not a0, a0
+; RV64I-NEXT:    ret
+;
+; RV64ZBB-ZBP-ZBKB-LABEL: not_shl_one_i64:
+; RV64ZBB-ZBP-ZBKB:       # %bb.0:
+; RV64ZBB-ZBP-ZBKB-NEXT:    li a1, -2
+; RV64ZBB-ZBP-ZBKB-NEXT:    rol a0, a1, a0
+; RV64ZBB-ZBP-ZBKB-NEXT:    ret
+  %1 = shl i64 1, %x
+  %2 = xor i64 %1, -1
+  ret i64 %2
+}
+
 define i8 @srli_i8(i8 %a) nounwind {
 ; RV64I-LABEL: srli_i8:
 ; RV64I:       # %bb.0:
 ; RV64I-NEXT:    slli a0, a0, 56
 ; RV64I-NEXT:    srli a0, a0, 62
 ; RV64I-NEXT:    ret
 ;
 ; RV64ZBB-ZBP-ZBKB-LABEL: srli_i8:

llvm/test/CodeGen/RISCV/sextw-removal.ll

 ; RV64I-NEXT:    sllw a1, a2, a1
 ; RV64I-NEXT:    not a1, a1
 ; RV64I-NEXT:    and a0, a1, a0
 ; RV64I-NEXT:    ret
 ;
 ; RV64ZBB-LABEL: test2:
 ; RV64ZBB:       # %bb.0:
 ; RV64ZBB-NEXT:    lw a0, 0(a0)
-; RV64ZBB-NEXT:    li a2, 1
-; RV64ZBB-NEXT:    sllw a1, a2, a1
-; RV64ZBB-NEXT:    andn a0, a0, a1
+; RV64ZBB-NEXT:    li a2, -2
+; RV64ZBB-NEXT:    rolw a1, a2, a1
+; RV64ZBB-NEXT:    and a0, a1, a0
 ; RV64ZBB-NEXT:    ret
 ;
 ; NOREMOVAL-LABEL: test2:
 ; NOREMOVAL:       # %bb.0:
 ; NOREMOVAL-NEXT:    lw a0, 0(a0)
-; NOREMOVAL-NEXT:    li a2, 1
-; NOREMOVAL-NEXT:    sllw a1, a2, a1
-; NOREMOVAL-NEXT:    andn a0, a0, a1
+; NOREMOVAL-NEXT:    li a2, -2
+; NOREMOVAL-NEXT:    rolw a1, a2, a1
+; NOREMOVAL-NEXT:    and a0, a1, a0
 ; NOREMOVAL-NEXT:    sext.w a0, a0
 ; NOREMOVAL-NEXT:    ret
   %a = load i32, i32* %p
   %shl = shl i32 1, %b
   %neg = xor i32 %shl, -1
   %and1 = and i32 %neg, %a
   ret i32 %and1
 }
 
 define signext i32 @test3(i32* %p, i32 signext %b) nounwind {
 ; RV64I-LABEL: test3:
 ; RV64I:       # %bb.0:
 ; RV64I-NEXT:    lw a0, 0(a0)
 ; RV64I-NEXT:    li a2, 1
 ; RV64I-NEXT:    sllw a1, a2, a1
 ; RV64I-NEXT:    not a1, a1
 ; RV64I-NEXT:    or a0, a1, a0
 ; RV64I-NEXT:    ret
 ;
 ; RV64ZBB-LABEL: test3:
 ; RV64ZBB:       # %bb.0:
 ; RV64ZBB-NEXT:    lw a0, 0(a0)
-; RV64ZBB-NEXT:    li a2, 1
-; RV64ZBB-NEXT:    sllw a1, a2, a1
-; RV64ZBB-NEXT:    orn a0, a0, a1
+; RV64ZBB-NEXT:    li a2, -2
+; RV64ZBB-NEXT:    rolw a1, a2, a1
+; RV64ZBB-NEXT:    or a0, a1, a0
 ; RV64ZBB-NEXT:    ret
 ;
 ; NOREMOVAL-LABEL: test3:
 ; NOREMOVAL:       # %bb.0:
 ; NOREMOVAL-NEXT:    lw a0, 0(a0)
-; NOREMOVAL-NEXT:    li a2, 1
-; NOREMOVAL-NEXT:    sllw a1, a2, a1
-; NOREMOVAL-NEXT:    orn a0, a0, a1
+; NOREMOVAL-NEXT:    li a2, -2
+; NOREMOVAL-NEXT:    rolw a1, a2, a1
+; NOREMOVAL-NEXT:    or a0, a1, a0
 ; NOREMOVAL-NEXT:    sext.w a0, a0
 ; NOREMOVAL-NEXT:    ret
   %a = load i32, i32* %p
   %shl = shl i32 1, %b
   %neg = xor i32 %shl, -1
   %and1 = or i32 %neg, %a
   ret i32 %and1
 }