diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -6888,6 +6888,10 @@
     assert(N->getValueType(0) == MVT::i32 && Subtarget.is64Bit() &&
            "Unexpected custom legalisation");
     if (N->getOperand(1).getOpcode() != ISD::Constant) {
+      // If we can use a BSET instruction, allow default promotion to apply.
+      if (N->getOpcode() == ISD::SHL && Subtarget.hasStdExtZbs() &&
+          isOneConstant(N->getOperand(0)))
+        break;
       Results.push_back(customLegalizeToWOp(N, DAG));
       break;
     }
diff --git a/llvm/test/CodeGen/RISCV/rv64zbs.ll b/llvm/test/CodeGen/RISCV/rv64zbs.ll
--- a/llvm/test/CodeGen/RISCV/rv64zbs.ll
+++ b/llvm/test/CodeGen/RISCV/rv64zbs.ll
@@ -15,10 +15,9 @@
 ;
 ; RV64ZBS-LABEL: bclr_i32:
 ; RV64ZBS:       # %bb.0:
-; RV64ZBS-NEXT:    li a2, 1
-; RV64ZBS-NEXT:    sllw a1, a2, a1
-; RV64ZBS-NEXT:    not a1, a1
-; RV64ZBS-NEXT:    and a0, a1, a0
+; RV64ZBS-NEXT:    andi a1, a1, 31
+; RV64ZBS-NEXT:    bclr a0, a0, a1
+; RV64ZBS-NEXT:    sext.w a0, a0
 ; RV64ZBS-NEXT:    ret
   %and = and i32 %b, 31
   %shl = shl nuw i32 1, %and
@@ -38,10 +37,8 @@
 ;
 ; RV64ZBS-LABEL: bclr_i32_no_mask:
 ; RV64ZBS:       # %bb.0:
-; RV64ZBS-NEXT:    li a2, 1
-; RV64ZBS-NEXT:    sllw a1, a2, a1
-; RV64ZBS-NEXT:    not a1, a1
-; RV64ZBS-NEXT:    and a0, a1, a0
+; RV64ZBS-NEXT:    bclr a0, a0, a1
+; RV64ZBS-NEXT:    sext.w a0, a0
 ; RV64ZBS-NEXT:    ret
   %shl = shl i32 1, %b
   %neg = xor i32 %shl, -1
@@ -62,10 +59,8 @@
 ; RV64ZBS-LABEL: bclr_i32_load:
 ; RV64ZBS:       # %bb.0:
 ; RV64ZBS-NEXT:    lw a0, 0(a0)
-; RV64ZBS-NEXT:    li a2, 1
-; RV64ZBS-NEXT:    sllw a1, a2, a1
-; RV64ZBS-NEXT:    not a1, a1
-; RV64ZBS-NEXT:    and a0, a1, a0
+; RV64ZBS-NEXT:    bclr a0, a0, a1
+; RV64ZBS-NEXT:    sext.w a0, a0
 ; RV64ZBS-NEXT:    ret
   %a = load i32, i32* %p
   %shl = shl i32 1, %b
@@ -123,9 +118,9 @@
 ;
 ; RV64ZBS-LABEL: bset_i32:
 ; RV64ZBS:       # %bb.0:
-; RV64ZBS-NEXT:    li a2, 1
-; RV64ZBS-NEXT:    sllw a1, a2, a1
-; RV64ZBS-NEXT:    or a0, a1, a0
+; RV64ZBS-NEXT:    andi a1, a1, 31
+; RV64ZBS-NEXT:    bset a0, a0, a1
+; RV64ZBS-NEXT:    sext.w a0, a0
 ; RV64ZBS-NEXT:    ret
   %and = and i32 %b, 31
   %shl = shl nuw i32 1, %and
@@ -143,9 +138,8 @@
 ;
 ; RV64ZBS-LABEL: bset_i32_no_mask:
 ; RV64ZBS:       # %bb.0:
-; RV64ZBS-NEXT:    li a2, 1
-; RV64ZBS-NEXT:    sllw a1, a2, a1
-; RV64ZBS-NEXT:    or a0, a1, a0
+; RV64ZBS-NEXT:    bset a0, a0, a1
+; RV64ZBS-NEXT:    sext.w a0, a0
 ; RV64ZBS-NEXT:    ret
   %shl = shl i32 1, %b
   %or = or i32 %shl, %a
@@ -164,9 +158,8 @@
 ; RV64ZBS-LABEL: bset_i32_load:
 ; RV64ZBS:       # %bb.0:
 ; RV64ZBS-NEXT:    lw a0, 0(a0)
-; RV64ZBS-NEXT:    li a2, 1
-; RV64ZBS-NEXT:    sllw a1, a2, a1
-; RV64ZBS-NEXT:    or a0, a1, a0
+; RV64ZBS-NEXT:    bset a0, a0, a1
+; RV64ZBS-NEXT:    sext.w a0, a0
 ; RV64ZBS-NEXT:    ret
   %a = load i32, i32* %p
   %shl = shl i32 1, %b
@@ -184,8 +177,8 @@
 ;
 ; RV64ZBS-LABEL: bset_i32_zero:
 ; RV64ZBS:       # %bb.0:
-; RV64ZBS-NEXT:    li a1, 1
-; RV64ZBS-NEXT:    sllw a0, a1, a0
+; RV64ZBS-NEXT:    bset a0, zero, a0
+; RV64ZBS-NEXT:    sext.w a0, a0
 ; RV64ZBS-NEXT:    ret
   %shl = shl i32 1, %a
   ret i32 %shl
@@ -252,9 +245,9 @@
 ;
 ; RV64ZBS-LABEL: binv_i32:
 ; RV64ZBS:       # %bb.0:
-; RV64ZBS-NEXT:    li a2, 1
-; RV64ZBS-NEXT:    sllw a1, a2, a1
-; RV64ZBS-NEXT:    xor a0, a1, a0
+; RV64ZBS-NEXT:    andi a1, a1, 31
+; RV64ZBS-NEXT:    binv a0, a0, a1
+; RV64ZBS-NEXT:    sext.w a0, a0
 ; RV64ZBS-NEXT:    ret
   %and = and i32 %b, 31
   %shl = shl nuw i32 1, %and
@@ -272,9 +265,8 @@
 ;
 ; RV64ZBS-LABEL: binv_i32_no_mask:
 ; RV64ZBS:       # %bb.0:
-; RV64ZBS-NEXT:    li a2, 1
-; RV64ZBS-NEXT:    sllw a1, a2, a1
-; RV64ZBS-NEXT:    xor a0, a1, a0
+; RV64ZBS-NEXT:    binv a0, a0, a1
+; RV64ZBS-NEXT:    sext.w a0, a0
 ; RV64ZBS-NEXT:    ret
   %shl = shl i32 1, %b
   %xor = xor i32 %shl, %a
@@ -293,9 +285,8 @@
 ; RV64ZBS-LABEL: binv_i32_load:
 ; RV64ZBS:       # %bb.0:
 ; RV64ZBS-NEXT:    lw a0, 0(a0)
-; RV64ZBS-NEXT:    li a2, 1
-; RV64ZBS-NEXT:    sllw a1, a2, a1
-; RV64ZBS-NEXT:    xor a0, a1, a0
+; RV64ZBS-NEXT:    binv a0, a0, a1
+; RV64ZBS-NEXT:    sext.w a0, a0
 ; RV64ZBS-NEXT:    ret
   %a = load i32, i32* %p
   %shl = shl i32 1, %b