Index: llvm/lib/Target/CSKY/CSKYInstrInfo.td
===================================================================
--- llvm/lib/Target/CSKY/CSKYInstrInfo.td
+++ llvm/lib/Target/CSKY/CSKYInstrInfo.td
@@ -102,6 +102,14 @@
   let DecoderMethod = "decodeOImmOperand<"#num#">";
 }
 
+def imm_neg_XFORM : SDNodeXForm<imm, [{
+  return CurDAG->getTargetConstant(-N->getSExtValue(), SDLoc(N), MVT::i32);
+}]>;
+
+class oimm_neg<int num> : Operand<i32>,
+  ImmLeaf<i32, "return isUInt<"#num#">(-Imm - 1);"> {
+}
+
 class uimm<int num, int shift = 0> : Operand<i32>,
   ImmLeaf<i32, "return isShiftedUInt<"#num#", "#shift#">(Imm);"> {
   let EncoderMethod = "getImmOpValue<"#shift#">";
@@ -259,6 +267,23 @@
   }];
 }
 
+def oimm8_neg : oimm_neg<8> {
+  let MCOperandPredicate = [{
+    int64_t Imm;
+    if (MCOp.evaluateAsConstantImm(Imm))
+      return isUInt<8>(-Imm - 1);
+    return MCOp.isBareSymbolRef();
+  }];
+}
+def oimm12_neg : oimm_neg<12> {
+  let MCOperandPredicate = [{
+    int64_t Imm;
+    if (MCOp.evaluateAsConstantImm(Imm))
+      return isUInt<12>(-Imm - 1);
+    return MCOp.isBareSymbolRef();
+  }];
+}
+
 def nimm12 : nimm<12>;
 
 def uimm1 : uimm<1>;
@@ -518,6 +543,9 @@
   let Size = 8 in
   def RSUBI32 : CSKYPseudo<(outs GPR:$rd), (ins GPR:$rx, uimm12:$imm12), "rsubi32 $rd, $rx, $imm12", []>;
 
+  def : Pat<(add GPR:$rs1, (oimm12_neg:$im)),
+            (SUBI32 GPR:$rs1, (imm_neg_XFORM oimm12_neg:$im))>;
+
   def LSL32 : R_YXZ_SP_F1<0x10, 0x1,
     BinOpFrag<(shl node:$LHS, node:$RHS)>, "lsl32">;
   def LSR32 : R_YXZ_SP_F1<0x10, 0x2,
Index: llvm/lib/Target/CSKY/CSKYInstrInfo16Instr.td
===================================================================
--- llvm/lib/Target/CSKY/CSKYInstrInfo16Instr.td
+++ llvm/lib/Target/CSKY/CSKYInstrInfo16Instr.td
@@ -97,6 +97,9 @@
   def SUBI16 : I16_Z_8<0b101, (ins mGPR:$rZ, oimm8:$imm8), "subi16\t$rz, $imm8">;
 }
 
+def : Pat<(add GPR:$rs1, (oimm8_neg:$im)),
+          (SUBI16 GPR:$rs1, (imm_neg_XFORM oimm8_neg:$im))>;
+
 let isAdd = 1 in
 def ADDI16ZSP : I16_Z_8<0b011, (ins GPRSP:$sp, uimm8_2:$imm8),
                         "addi16\t$rz, $sp, $imm8">;
Index: llvm/test/CodeGen/CSKY/base-i.ll
===================================================================
--- llvm/test/CodeGen/CSKY/base-i.ll
+++ llvm/test/CodeGen/CSKY/base-i.ll
@@ -40,6 +40,52 @@
   ret i32 %add
 }
 
+define i32 @addRI_256(i32 %x) {
+; CHECK-LABEL: addRI_256:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    addi16 a0, 256
+; CHECK-NEXT:    rts16
+;
+; GENERIC-LABEL: addRI_256:
+; GENERIC:       # %bb.0: # %entry
+; GENERIC-NEXT:    .cfi_def_cfa_offset 0
+; GENERIC-NEXT:    subi16 sp, sp, 4
+; GENERIC-NEXT:    .cfi_def_cfa_offset 4
+; GENERIC-NEXT:    addi16 a0, 256
+; GENERIC-NEXT:    addi16 sp, sp, 4
+; GENERIC-NEXT:    rts16
+entry:
+  %add = add nsw i32 %x, 256
+  ret i32 %add
+}
+
+define i32 @addRI_4096(i32 %x) {
+; CHECK-LABEL: addRI_4096:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    addi32 a0, a0, 4096
+; CHECK-NEXT:    rts16
+;
+; GENERIC-LABEL: addRI_4096:
+; GENERIC:       # %bb.0: # %entry
+; GENERIC-NEXT:    .cfi_def_cfa_offset 0
+; GENERIC-NEXT:    subi16 sp, sp, 4
+; GENERIC-NEXT:    .cfi_def_cfa_offset 4
+; GENERIC-NEXT:    movi16 a1, 0
+; GENERIC-NEXT:    lsli16 a2, a1, 24
+; GENERIC-NEXT:    lsli16 a3, a1, 16
+; GENERIC-NEXT:    or16 a3, a2
+; GENERIC-NEXT:    movi16 a2, 16
+; GENERIC-NEXT:    lsli16 a2, a2, 8
+; GENERIC-NEXT:    or16 a2, a3
+; GENERIC-NEXT:    or16 a2, a1
+; GENERIC-NEXT:    addu16 a0, a0, a2
+; GENERIC-NEXT:    addi16 sp, sp, 4
+; GENERIC-NEXT:    rts16
+entry:
+  %add = add nsw i32 %x, 4096
+  ret i32 %add
+}
+
 define i32 @addRI_X(i32 %x) {
 ; CHECK-LABEL: addRI_X:
 ; CHECK:       # %bb.0: # %entry
@@ -218,9 +264,7 @@
 define i32 @subRI(i32 %x) {
 ; CHECK-LABEL: subRI:
 ; CHECK:       # %bb.0: # %entry
-; CHECK-NEXT:    movih32 a1, 65535
-; CHECK-NEXT:    ori32 a1, a1, 65526
-; CHECK-NEXT:    addu16 a0, a1
+; CHECK-NEXT:    subi16 a0, 10
 ; CHECK-NEXT:    rts16
 ;
 ; GENERIC-LABEL: subRI:
@@ -228,19 +272,58 @@
 ; GENERIC-NEXT:    .cfi_def_cfa_offset 0
 ; GENERIC-NEXT:    subi16 sp, sp, 4
 ; GENERIC-NEXT:    .cfi_def_cfa_offset 4
+; GENERIC-NEXT:    subi16 a0, 10
+; GENERIC-NEXT:    addi16 sp, sp, 4
+; GENERIC-NEXT:    rts16
+entry:
+  %sub = sub nsw i32 %x, 10
+  ret i32 %sub
+}
+
+define i32 @subRI_256(i32 %x) {
+; CHECK-LABEL: subRI_256:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    subi16 a0, 256
+; CHECK-NEXT:    rts16
+;
+; GENERIC-LABEL: subRI_256:
+; GENERIC:       # %bb.0: # %entry
+; GENERIC-NEXT:    .cfi_def_cfa_offset 0
+; GENERIC-NEXT:    subi16 sp, sp, 4
+; GENERIC-NEXT:    .cfi_def_cfa_offset 4
+; GENERIC-NEXT:    subi16 a0, 256
+; GENERIC-NEXT:    addi16 sp, sp, 4
+; GENERIC-NEXT:    rts16
+entry:
+  %sub = sub nsw i32 %x, 256
+  ret i32 %sub
+}
+
+define i32 @subRI_4096(i32 %x) {
+; CHECK-LABEL: subRI_4096:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    subi32 a0, a0, 4096
+; CHECK-NEXT:    rts16
+;
+; GENERIC-LABEL: subRI_4096:
+; GENERIC:       # %bb.0: # %entry
+; GENERIC-NEXT:    .cfi_def_cfa_offset 0
+; GENERIC-NEXT:    subi16 sp, sp, 4
+; GENERIC-NEXT:    .cfi_def_cfa_offset 4
 ; GENERIC-NEXT:    movi16 a1, 255
 ; GENERIC-NEXT:    lsli16 a2, a1, 24
-; GENERIC-NEXT:    lsli16 a3, a1, 16
-; GENERIC-NEXT:    or16 a3, a2
-; GENERIC-NEXT:    lsli16 a1, a1, 8
-; GENERIC-NEXT:    or16 a1, a3
-; GENERIC-NEXT:    movi16 a2, 246
+; GENERIC-NEXT:    lsli16 a1, a1, 16
+; GENERIC-NEXT:    or16 a1, a2
+; GENERIC-NEXT:    movi16 a2, 240
+; GENERIC-NEXT:    lsli16 a2, a2, 8
 ; GENERIC-NEXT:    or16 a2, a1
-; GENERIC-NEXT:    addu16 a0, a0, a2
+; GENERIC-NEXT:    movi16 a1, 0
+; GENERIC-NEXT:    or16 a1, a2
+; GENERIC-NEXT:    addu16 a0, a0, a1
 ; GENERIC-NEXT:    addi16 sp, sp, 4
 ; GENERIC-NEXT:    rts16
 entry:
-  %sub = sub nsw i32 %x, 10
+  %sub = sub nsw i32 %x, 4096
   ret i32 %sub
 }
 
@@ -365,9 +448,7 @@
 define i16 @SUB_SHORT_I(i16 %x) {
 ; CHECK-LABEL: SUB_SHORT_I:
 ; CHECK:       # %bb.0: # %entry
-; CHECK-NEXT:    movih32 a1, 65535
-; CHECK-NEXT:    ori32 a1, a1, 65535
-; CHECK-NEXT:    addu16 a0, a1
+; CHECK-NEXT:    subi16 a0, a0, 1
 ; CHECK-NEXT:    rts16
 ;
 ; GENERIC-LABEL: SUB_SHORT_I:
@@ -375,14 +456,7 @@
 ; GENERIC-NEXT:    .cfi_def_cfa_offset 0
 ; GENERIC-NEXT:    subi16 sp, sp, 4
 ; GENERIC-NEXT:    .cfi_def_cfa_offset 4
-; GENERIC-NEXT:    movi16 a1, 255
-; GENERIC-NEXT:    lsli16 a2, a1, 24
-; GENERIC-NEXT:    lsli16 a3, a1, 16
-; GENERIC-NEXT:    or16 a3, a2
-; GENERIC-NEXT:    lsli16 a2, a1, 8
-; GENERIC-NEXT:    or16 a2, a3
-; GENERIC-NEXT:    or16 a2, a1
-; GENERIC-NEXT:    addu16 a0, a0, a2
+; GENERIC-NEXT:    subi16 a0, 1
 ; GENERIC-NEXT:    addi16 sp, sp, 4
 ; GENERIC-NEXT:    rts16
 entry:
@@ -412,9 +486,7 @@
 define i8 @SUB_CHAR_I(i8 %x) {
 ; CHECK-LABEL: SUB_CHAR_I:
 ; CHECK:       # %bb.0: # %entry
-; CHECK-NEXT:    movih32 a1, 65535
-; CHECK-NEXT:    ori32 a1, a1, 65535
-; CHECK-NEXT:    addu16 a0, a1
+; CHECK-NEXT:    subi16 a0, a0, 1
 ; CHECK-NEXT:    rts16
 ;
 ; GENERIC-LABEL: SUB_CHAR_I:
@@ -422,14 +494,7 @@
 ; GENERIC-NEXT:    .cfi_def_cfa_offset 0
 ; GENERIC-NEXT:    subi16 sp, sp, 4
 ; GENERIC-NEXT:    .cfi_def_cfa_offset 4
-; GENERIC-NEXT:    movi16 a1, 255
-; GENERIC-NEXT:    lsli16 a2, a1, 24
-; GENERIC-NEXT:    lsli16 a3, a1, 16
-; GENERIC-NEXT:    or16 a3, a2
-; GENERIC-NEXT:    lsli16 a2, a1, 8
-; GENERIC-NEXT:    or16 a2, a3
-; GENERIC-NEXT:    or16 a2, a1
-; GENERIC-NEXT:    addu16 a0, a0, a2
+; GENERIC-NEXT:    subi16 a0, 1
 ; GENERIC-NEXT:    addi16 sp, sp, 4
 ; GENERIC-NEXT:    rts16
 entry:
@@ -595,7 +660,7 @@
 ; GENERIC-NEXT:    subi16 sp, sp, 4
 ; GENERIC-NEXT:    .cfi_def_cfa_offset 8
 ; GENERIC-NEXT:    mov16 a2, a0
-; GENERIC-NEXT:    lrw32 a3, [.LCPI25_0]
+; GENERIC-NEXT:    lrw32 a3, [.LCPI29_0]
 ; GENERIC-NEXT:    mov16 a0, a1
 ; GENERIC-NEXT:    mov16 a1, a2
 ; GENERIC-NEXT:    jsr16 a3
@@ -606,7 +671,7 @@
 ; GENERIC-NEXT:    .p2align 1
 ; GENERIC-NEXT:  # %bb.1:
 ; GENERIC-NEXT:    .p2align 2, 0x0
-; GENERIC-NEXT:  .LCPI25_0:
+; GENERIC-NEXT:  .LCPI29_0:
 ; GENERIC-NEXT:    .long __udivsi3
 entry:
   %udiv = udiv  i32 %y, %x
@@ -628,7 +693,7 @@
 ; GENERIC-NEXT:    .cfi_offset lr, -4
 ; GENERIC-NEXT:    subi16 sp, sp, 4
 ; GENERIC-NEXT:    .cfi_def_cfa_offset 8
-; GENERIC-NEXT:    lrw32 a2, [.LCPI26_0]
+; GENERIC-NEXT:    lrw32 a2, [.LCPI30_0]
 ; GENERIC-NEXT:    movi16 a1, 10
 ; GENERIC-NEXT:    jsr16 a2
 ; GENERIC-NEXT:    addi16 sp, sp, 4
@@ -638,7 +703,7 @@
 ; GENERIC-NEXT:    .p2align 1
 ; GENERIC-NEXT:  # %bb.1:
 ; GENERIC-NEXT:    .p2align 2, 0x0
-; GENERIC-NEXT:  .LCPI26_0:
+; GENERIC-NEXT:  .LCPI30_0:
 ; GENERIC-NEXT:    .long __udivsi3
 entry:
   %udiv = udiv  i32 %x, 10
@@ -669,7 +734,7 @@
 ; GENERIC-NEXT:    or16 a2, a1
 ; GENERIC-NEXT:    movi16 a1, 1
 ; GENERIC-NEXT:    or16 a1, a2
-; GENERIC-NEXT:    lrw32 a2, [.LCPI27_0]
+; GENERIC-NEXT:    lrw32 a2, [.LCPI31_0]
 ; GENERIC-NEXT:    jsr16 a2
 ; GENERIC-NEXT:    addi16 sp, sp, 4
 ; GENERIC-NEXT:    ld32.w lr, (sp, 0) # 4-byte Folded Reload
@@ -678,7 +743,7 @@
 ; GENERIC-NEXT:    .p2align 1
 ; GENERIC-NEXT:  # %bb.1:
 ; GENERIC-NEXT:    .p2align 2, 0x0
-; GENERIC-NEXT:  .LCPI27_0:
+; GENERIC-NEXT:  .LCPI31_0:
 ; GENERIC-NEXT:    .long __udivsi3
 entry:
   %udiv = udiv  i32 %x, 4097
@@ -714,7 +779,7 @@
 ; GENERIC-NEXT:    or16 a1, a3
 ; GENERIC-NEXT:    and16 a2, a1
 ; GENERIC-NEXT:    and16 a1, a0
-; GENERIC-NEXT:    lrw32 a3, [.LCPI28_0]
+; GENERIC-NEXT:    lrw32 a3, [.LCPI32_0]
 ; GENERIC-NEXT:    mov16 a0, a2
 ; GENERIC-NEXT:    jsr16 a3
 ; GENERIC-NEXT:    addi16 sp, sp, 4
@@ -725,7 +790,7 @@
 ; GENERIC-NEXT:    .p2align 1
 ; GENERIC-NEXT:  # %bb.1:
 ; GENERIC-NEXT:    .p2align 2, 0x0
-; GENERIC-NEXT:  .LCPI28_0:
+; GENERIC-NEXT:  .LCPI32_0:
 ; GENERIC-NEXT:    .long __udivsi3
 entry:
   %udiv = udiv  i16 %y, %x
@@ -789,7 +854,7 @@
 ; GENERIC-NEXT:    movi16 a1, 255
 ; GENERIC-NEXT:    and16 a2, a1
 ; GENERIC-NEXT:    and16 a1, a0
-; GENERIC-NEXT:    lrw32 a3, [.LCPI30_0]
+; GENERIC-NEXT:    lrw32 a3, [.LCPI34_0]
 ; GENERIC-NEXT:    mov16 a0, a2
 ; GENERIC-NEXT:    jsr16 a3
 ; GENERIC-NEXT:    addi16 sp, sp, 4
@@ -799,7 +864,7 @@
 ; GENERIC-NEXT:    .p2align 1
 ; GENERIC-NEXT:  # %bb.1:
 ; GENERIC-NEXT:    .p2align 2, 0x0
-; GENERIC-NEXT:  .LCPI30_0:
+; GENERIC-NEXT:  .LCPI34_0:
 ; GENERIC-NEXT:    .long __udivsi3
 entry:
   %udiv = udiv  i8 %y, %x
@@ -847,7 +912,7 @@
 ; GENERIC-NEXT:    subi16 sp, sp, 4
 ; GENERIC-NEXT:    .cfi_def_cfa_offset 8
 ; GENERIC-NEXT:    mov16 a2, a0
-; GENERIC-NEXT:    lrw32 a3, [.LCPI32_0]
+; GENERIC-NEXT:    lrw32 a3, [.LCPI36_0]
 ; GENERIC-NEXT:    mov16 a0, a1
 ; GENERIC-NEXT:    mov16 a1, a2
 ; GENERIC-NEXT:    jsr16 a3
@@ -858,7 +923,7 @@
 ; GENERIC-NEXT:    .p2align 1
 ; GENERIC-NEXT:  # %bb.1:
 ; GENERIC-NEXT:    .p2align 2, 0x0
-; GENERIC-NEXT:  .LCPI32_0:
+; GENERIC-NEXT:  .LCPI36_0:
 ; GENERIC-NEXT:    .long __divsi3
 entry:
   %sdiv = sdiv  i32 %y, %x
@@ -880,7 +945,7 @@
 ; GENERIC-NEXT:    .cfi_offset lr, -4
 ; GENERIC-NEXT:    subi16 sp, sp, 4
 ; GENERIC-NEXT:    .cfi_def_cfa_offset 8
-; GENERIC-NEXT:    lrw32 a2, [.LCPI33_0]
+; GENERIC-NEXT:    lrw32 a2, [.LCPI37_0]
 ; GENERIC-NEXT:    movi16 a1, 10
 ; GENERIC-NEXT:    jsr16 a2
 ; GENERIC-NEXT:    addi16 sp, sp, 4
@@ -890,7 +955,7 @@
 ; GENERIC-NEXT:    .p2align 1
 ; GENERIC-NEXT:  # %bb.1:
 ; GENERIC-NEXT:    .p2align 2, 0x0
-; GENERIC-NEXT:  .LCPI33_0:
+; GENERIC-NEXT:  .LCPI37_0:
 ; GENERIC-NEXT:    .long __divsi3
 entry:
   %sdiv = sdiv  i32 %x, 10
@@ -921,7 +986,7 @@
 ; GENERIC-NEXT:    or16 a2, a1
 ; GENERIC-NEXT:    movi16 a1, 1
 ; GENERIC-NEXT:    or16 a1, a2
-; GENERIC-NEXT:    lrw32 a2, [.LCPI34_0]
+; GENERIC-NEXT:    lrw32 a2, [.LCPI38_0]
 ; GENERIC-NEXT:    jsr16 a2
 ; GENERIC-NEXT:    addi16 sp, sp, 4
 ; GENERIC-NEXT:    ld32.w lr, (sp, 0) # 4-byte Folded Reload
@@ -930,7 +995,7 @@
 ; GENERIC-NEXT:    .p2align 1
 ; GENERIC-NEXT:  # %bb.1:
 ; GENERIC-NEXT:    .p2align 2, 0x0
-; GENERIC-NEXT:  .LCPI34_0:
+; GENERIC-NEXT:  .LCPI38_0:
 ; GENERIC-NEXT:    .long __divsi3
 entry:
   %sdiv = sdiv  i32 %x, 4097
@@ -955,7 +1020,7 @@
 ; GENERIC-NEXT:    .cfi_def_cfa_offset 8
 ; GENERIC-NEXT:    sexth16 a2, a1
 ; GENERIC-NEXT:    sexth16 a1, a0
-; GENERIC-NEXT:    lrw32 a3, [.LCPI35_0]
+; GENERIC-NEXT:    lrw32 a3, [.LCPI39_0]
 ; GENERIC-NEXT:    mov16 a0, a2
 ; GENERIC-NEXT:    jsr16 a3
 ; GENERIC-NEXT:    addi16 sp, sp, 4
@@ -965,7 +1030,7 @@
 ; GENERIC-NEXT:    .p2align 1
 ; GENERIC-NEXT:  # %bb.1:
 ; GENERIC-NEXT:    .p2align 2, 0x0
-; GENERIC-NEXT:  .LCPI35_0:
+; GENERIC-NEXT:  .LCPI39_0:
 ; GENERIC-NEXT:    .long __divsi3
 entry:
   %sdiv = sdiv  i16 %y, %x
@@ -1027,7 +1092,7 @@
 ; GENERIC-NEXT:    .cfi_def_cfa_offset 8
 ; GENERIC-NEXT:    sextb16 a2, a1
 ; GENERIC-NEXT:    sextb16 a1, a0
-; GENERIC-NEXT:    lrw32 a3, [.LCPI37_0]
+; GENERIC-NEXT:    lrw32 a3, [.LCPI41_0]
 ; GENERIC-NEXT:    mov16 a0, a2
 ; GENERIC-NEXT:    jsr16 a3
 ; GENERIC-NEXT:    addi16 sp, sp, 4
@@ -1037,7 +1102,7 @@
 ; GENERIC-NEXT:    .p2align 1
 ; GENERIC-NEXT:  # %bb.1:
 ; GENERIC-NEXT:    .p2align 2, 0x0
-; GENERIC-NEXT:  .LCPI37_0:
+; GENERIC-NEXT:  .LCPI41_0:
 ; GENERIC-NEXT:    .long __divsi3
 entry:
   %sdiv = sdiv  i8 %y, %x