[RISCV] Lower (setugt X, 2047) as (setne (srl X, 11), 0) (#155541)

This matches 4095 and other pow2-1 constants larger simm12. We normally
do this through a DAGCombine controlled by isLegalICmpImmediate. 2047 is
considered a legal immediate because we have a setult instruction. In
this case we have setugt which isn't natively supported.

I added tests for 4095 for comparison.

Author: topperc

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -8193,6 +8193,13 @@ SDValue RISCVTargetLowering::LowerOperation(SDValue Op,
               DL, VT, LHS, DAG.getSignedConstant(Imm + 1, DL, OpVT), CCVal);
           return DAG.getLogicalNOT(DL, SetCC, VT);
         }
+        // Lower (setugt X, 2047) as (setne (srl X, 11), 0).
+        if (CCVal == ISD::SETUGT && Imm == 2047) {
+          SDValue Shift = DAG.getNode(ISD::SRL, DL, OpVT, LHS,
+                                      DAG.getShiftAmountConstant(11, OpVT, DL));
+          return DAG.getSetCC(DL, VT, Shift, DAG.getConstant(0, DL, OpVT),
+                              ISD::SETNE);
+        }
       }
 
       // Not a constant we could handle, swap the operands and condition code to

llvm/test/CodeGen/RISCV/i32-icmp.ll

@@ -366,20 +366,37 @@ define i32 @icmp_ugt_constant_zero(i32 %a) nounwind {
 define i32 @icmp_ugt_constant_2047(i32 %a) nounwind {
 ; RV32I-LABEL: icmp_ugt_constant_2047:
 ; RV32I:       # %bb.0:
-; RV32I-NEXT:    li a1, 2047
-; RV32I-NEXT:    sltu a0, a1, a0
+; RV32I-NEXT:    srli a0, a0, 11
+; RV32I-NEXT:    snez a0, a0
 ; RV32I-NEXT:    ret
 ;
 ; RV32XQCILIA-LABEL: icmp_ugt_constant_2047:
 ; RV32XQCILIA:       # %bb.0:
-; RV32XQCILIA-NEXT:    li a1, 2047
-; RV32XQCILIA-NEXT:    sltu a0, a1, a0
+; RV32XQCILIA-NEXT:    srli a0, a0, 11
+; RV32XQCILIA-NEXT:    snez a0, a0
 ; RV32XQCILIA-NEXT:    ret
   %1 = icmp ugt i32 %a, 2047
   %2 = zext i1 %1 to i32
   ret i32 %2
 }
 
+define i32 @icmp_ugt_constant_4095(i32 %a) nounwind {
+; RV32I-LABEL: icmp_ugt_constant_4095:
+; RV32I:       # %bb.0:
+; RV32I-NEXT:    srli a0, a0, 12
+; RV32I-NEXT:    snez a0, a0
+; RV32I-NEXT:    ret
+;
+; RV32XQCILIA-LABEL: icmp_ugt_constant_4095:
+; RV32XQCILIA:       # %bb.0:
+; RV32XQCILIA-NEXT:    srli a0, a0, 12
+; RV32XQCILIA-NEXT:    snez a0, a0
+; RV32XQCILIA-NEXT:    ret
+  %1 = icmp ugt i32 %a, 4095
+  %2 = zext i1 %1 to i32
+  ret i32 %2
+}
+
 define i32 @icmp_ugt_constant_2046(i32 %a) nounwind {
 ; RV32I-LABEL: icmp_ugt_constant_2046:
 ; RV32I:       # %bb.0:
@@ -487,14 +504,14 @@ define i32 @icmp_uge_constant_2047(i32 %a) nounwind {
 define i32 @icmp_uge_constant_2048(i32 %a) nounwind {
 ; RV32I-LABEL: icmp_uge_constant_2048:
 ; RV32I:       # %bb.0:
-; RV32I-NEXT:    li a1, 2047
-; RV32I-NEXT:    sltu a0, a1, a0
+; RV32I-NEXT:    srli a0, a0, 11
+; RV32I-NEXT:    snez a0, a0
 ; RV32I-NEXT:    ret
 ;
 ; RV32XQCILIA-LABEL: icmp_uge_constant_2048:
 ; RV32XQCILIA:       # %bb.0:
-; RV32XQCILIA-NEXT:    li a1, 2047
-; RV32XQCILIA-NEXT:    sltu a0, a1, a0
+; RV32XQCILIA-NEXT:    srli a0, a0, 11
+; RV32XQCILIA-NEXT:    snez a0, a0
 ; RV32XQCILIA-NEXT:    ret
   %1 = icmp uge i32 %a, 2048
   %2 = zext i1 %1 to i32

llvm/test/CodeGen/RISCV/i64-icmp.ll

@@ -191,14 +191,25 @@ define i64 @icmp_ugt_constant_zero(i64 %a) nounwind {
 define i64 @icmp_ugt_constant_2047(i64 %a) nounwind {
 ; RV64I-LABEL: icmp_ugt_constant_2047:
 ; RV64I:       # %bb.0:
-; RV64I-NEXT:    li a1, 2047
-; RV64I-NEXT:    sltu a0, a1, a0
+; RV64I-NEXT:    srli a0, a0, 11
+; RV64I-NEXT:    snez a0, a0
 ; RV64I-NEXT:    ret
   %1 = icmp ugt i64 %a, 2047
   %2 = zext i1 %1 to i64
   ret i64 %2
 }
 
+define i64 @icmp_ugt_constant_4095(i64 %a) nounwind {
+; RV64I-LABEL: icmp_ugt_constant_4095:
+; RV64I:       # %bb.0:
+; RV64I-NEXT:    srli a0, a0, 12
+; RV64I-NEXT:    snez a0, a0
+; RV64I-NEXT:    ret
+  %1 = icmp ugt i64 %a, 4095
+  %2 = zext i1 %1 to i64
+  ret i64 %2
+}
+
 define i64 @icmp_ugt_constant_2046(i64 %a) nounwind {
 ; RV64I-LABEL: icmp_ugt_constant_2046:
 ; RV64I:       # %bb.0:
@@ -270,8 +281,8 @@ define i64 @icmp_uge_constant_2047(i64 %a) nounwind {
 define i64 @icmp_uge_constant_2048(i64 %a) nounwind {
 ; RV64I-LABEL: icmp_uge_constant_2048:
 ; RV64I:       # %bb.0:
-; RV64I-NEXT:    li a1, 2047
-; RV64I-NEXT:    sltu a0, a1, a0
+; RV64I-NEXT:    srli a0, a0, 11
+; RV64I-NEXT:    snez a0, a0
 ; RV64I-NEXT:    ret
   %1 = icmp uge i64 %a, 2048
   %2 = zext i1 %1 to i64
@@ -754,10 +765,10 @@ define i64 @icmp_ne_zext_inreg_umin(i64 %a) nounwind {
 ; RV64I:       # %bb.0:
 ; RV64I-NEXT:    lui a1, 30141
 ; RV64I-NEXT:    addi a1, a1, -747
-; RV64I-NEXT:    bltu a0, a1, .LBB67_2
+; RV64I-NEXT:    bltu a0, a1, .LBB68_2
 ; RV64I-NEXT:  # %bb.1:
 ; RV64I-NEXT:    mv a0, a1
-; RV64I-NEXT:  .LBB67_2:
+; RV64I-NEXT:  .LBB68_2:
 ; RV64I-NEXT:    addi a0, a0, -123
 ; RV64I-NEXT:    snez a0, a0
 ; RV64I-NEXT:    ret