Index: llvm/lib/CodeGen/CodeGenPrepare.cpp
===================================================================
--- llvm/lib/CodeGen/CodeGenPrepare.cpp
+++ llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -2057,7 +2057,7 @@
     return false;
 
   // Bail if the value is never zero.
-  Value *Op = CountZeros->getOperand(0);
+  Use &Op = CountZeros->getOperandUse(0);
   if (isKnownNonZero(Op, *DL))
     return false;
 
@@ -2079,7 +2079,7 @@
   // Replace the unconditional branch that was created by the first split with
   // a compare against zero and a conditional branch.
   Value *Zero = Constant::getNullValue(Ty);
-  // Avoid introducing branch on poison.
+  // Avoid introducing branch on poison. This also replaces the ctz operand.
   if (!isGuaranteedNotToBeUndefOrPoison(Op))
     Op = Builder.CreateFreeze(Op, Op->getName() + ".fr");
   Value *Cmp = Builder.CreateICmpEQ(Op, Zero, "cmpz");
Index: llvm/test/CodeGen/RISCV/rv64zbb.ll
===================================================================
--- llvm/test/CodeGen/RISCV/rv64zbb.ll
+++ llvm/test/CodeGen/RISCV/rv64zbb.ll
@@ -11,7 +11,8 @@
 ; RV64I:       # %bb.0:
 ; RV64I-NEXT:    addi sp, sp, -16
 ; RV64I-NEXT:    sd ra, 8(sp) # 8-byte Folded Spill
-; RV64I-NEXT:    beqz a0, .LBB0_2
+; RV64I-NEXT:    sext.w a1, a0
+; RV64I-NEXT:    beqz a1, .LBB0_2
 ; RV64I-NEXT:  # %bb.1: # %cond.false
 ; RV64I-NEXT:    srliw a1, a0, 1
 ; RV64I-NEXT:    or a0, a0, a1
@@ -65,7 +66,8 @@
 ; RV64I:       # %bb.0:
 ; RV64I-NEXT:    addi sp, sp, -16
 ; RV64I-NEXT:    sd ra, 8(sp) # 8-byte Folded Spill
-; RV64I-NEXT:    beqz a0, .LBB1_2
+; RV64I-NEXT:    sext.w a1, a0
+; RV64I-NEXT:    beqz a1, .LBB1_2
 ; RV64I-NEXT:  # %bb.1: # %cond.false
 ; RV64I-NEXT:    srliw a1, a0, 1
 ; RV64I-NEXT:    or a0, a0, a1
@@ -257,16 +259,15 @@
 ; RV64I-NEXT:    srliw a0, a0, 1
 ; RV64I-NEXT:    beqz a0, .LBB4_2
 ; RV64I-NEXT:  # %bb.1: # %cond.false
-; RV64I-NEXT:    srli a1, a0, 1
+; RV64I-NEXT:    srliw a1, a0, 1
 ; RV64I-NEXT:    or a0, a0, a1
-; RV64I-NEXT:    srli a1, a0, 2
+; RV64I-NEXT:    srliw a1, a0, 2
 ; RV64I-NEXT:    or a0, a0, a1
-; RV64I-NEXT:    srli a1, a0, 4
+; RV64I-NEXT:    srliw a1, a0, 4
 ; RV64I-NEXT:    or a0, a0, a1
-; RV64I-NEXT:    srli a1, a0, 8
+; RV64I-NEXT:    srliw a1, a0, 8
 ; RV64I-NEXT:    or a0, a0, a1
-; RV64I-NEXT:    slli a1, a0, 33
-; RV64I-NEXT:    srli a1, a1, 49
+; RV64I-NEXT:    srliw a1, a0, 16
 ; RV64I-NEXT:    or a0, a0, a1
 ; RV64I-NEXT:    not a0, a0
 ; RV64I-NEXT:    srli a1, a0, 1
@@ -372,7 +373,8 @@
 ; RV64I:       # %bb.0:
 ; RV64I-NEXT:    addi sp, sp, -16
 ; RV64I-NEXT:    sd ra, 8(sp) # 8-byte Folded Spill
-; RV64I-NEXT:    beqz a0, .LBB6_2
+; RV64I-NEXT:    sext.w a1, a0
+; RV64I-NEXT:    beqz a1, .LBB6_2
 ; RV64I-NEXT:  # %bb.1: # %cond.false
 ; RV64I-NEXT:    addiw a1, a0, -1
 ; RV64I-NEXT:    not a0, a0
Index: llvm/test/Transforms/CodeGenPrepare/X86/cttz-ctlz.ll
===================================================================
--- llvm/test/Transforms/CodeGenPrepare/X86/cttz-ctlz.ll
+++ llvm/test/Transforms/CodeGenPrepare/X86/cttz-ctlz.ll
@@ -17,7 +17,7 @@
 ; SLOW-NEXT:    [[CMPZ:%.*]] = icmp eq i64 [[A_FR]], 0
 ; SLOW-NEXT:    br i1 [[CMPZ]], label [[COND_END:%.*]], label [[COND_FALSE:%.*]]
 ; SLOW:       cond.false:
-; SLOW-NEXT:    [[Z:%.*]] = call i64 @llvm.cttz.i64(i64 [[A]], i1 true)
+; SLOW-NEXT:    [[Z:%.*]] = call i64 @llvm.cttz.i64(i64 [[A_FR]], i1 true)
 ; SLOW-NEXT:    br label [[COND_END]]
 ; SLOW:       cond.end:
 ; SLOW-NEXT:    [[CTZ:%.*]] = phi i64 [ 64, [[ENTRY:%.*]] ], [ [[Z]], [[COND_FALSE]] ]
@@ -34,7 +34,7 @@
 ; FAST_LZ-NEXT:    [[CMPZ:%.*]] = icmp eq i64 [[A_FR]], 0
 ; FAST_LZ-NEXT:    br i1 [[CMPZ]], label [[COND_END:%.*]], label [[COND_FALSE:%.*]]
 ; FAST_LZ:       cond.false:
-; FAST_LZ-NEXT:    [[Z:%.*]] = call i64 @llvm.cttz.i64(i64 [[A]], i1 true)
+; FAST_LZ-NEXT:    [[Z:%.*]] = call i64 @llvm.cttz.i64(i64 [[A_FR]], i1 true)
 ; FAST_LZ-NEXT:    br label [[COND_END]]
 ; FAST_LZ:       cond.end:
 ; FAST_LZ-NEXT:    [[CTZ:%.*]] = phi i64 [ 64, [[ENTRY:%.*]] ], [ [[Z]], [[COND_FALSE]] ]
@@ -52,7 +52,7 @@
 ; SLOW-NEXT:    [[CMPZ:%.*]] = icmp eq i64 [[A_FR]], 0
 ; SLOW-NEXT:    br i1 [[CMPZ]], label [[COND_END:%.*]], label [[COND_FALSE:%.*]]
 ; SLOW:       cond.false:
-; SLOW-NEXT:    [[Z:%.*]] = call i64 @llvm.ctlz.i64(i64 [[A]], i1 true)
+; SLOW-NEXT:    [[Z:%.*]] = call i64 @llvm.ctlz.i64(i64 [[A_FR]], i1 true)
 ; SLOW-NEXT:    br label [[COND_END]]
 ; SLOW:       cond.end:
 ; SLOW-NEXT:    [[CTZ:%.*]] = phi i64 [ 64, [[ENTRY:%.*]] ], [ [[Z]], [[COND_FALSE]] ]
@@ -64,7 +64,7 @@
 ; FAST_TZ-NEXT:    [[CMPZ:%.*]] = icmp eq i64 [[A_FR]], 0
 ; FAST_TZ-NEXT:    br i1 [[CMPZ]], label [[COND_END:%.*]], label [[COND_FALSE:%.*]]
 ; FAST_TZ:       cond.false:
-; FAST_TZ-NEXT:    [[Z:%.*]] = call i64 @llvm.ctlz.i64(i64 [[A]], i1 true)
+; FAST_TZ-NEXT:    [[Z:%.*]] = call i64 @llvm.ctlz.i64(i64 [[A_FR]], i1 true)
 ; FAST_TZ-NEXT:    br label [[COND_END]]
 ; FAST_TZ:       cond.end:
 ; FAST_TZ-NEXT:    [[CTZ:%.*]] = phi i64 [ 64, [[ENTRY:%.*]] ], [ [[Z]], [[COND_FALSE]] ]