diff --git a/llvm/include/llvm/Support/KnownBits.h b/llvm/include/llvm/Support/KnownBits.h
--- a/llvm/include/llvm/Support/KnownBits.h
+++ b/llvm/include/llvm/Support/KnownBits.h
@@ -420,6 +420,11 @@
 
   void print(raw_ostream &OS) const;
   void dump() const;
+
+private:
+  // Internal helper for getting the initial KnownBits for an `srem` or `urem`
+  // operation with the low-bits set.
+  static KnownBits remGetLowBits(const KnownBits &LHS, const KnownBits &RHS);
 };
 
 inline KnownBits operator&(KnownBits LHS, const KnownBits &RHS) {
diff --git a/llvm/lib/Support/KnownBits.cpp b/llvm/lib/Support/KnownBits.cpp
--- a/llvm/lib/Support/KnownBits.cpp
+++ b/llvm/lib/Support/KnownBits.cpp
@@ -546,16 +546,28 @@
   return Known;
 }
 
-KnownBits KnownBits::urem(const KnownBits &LHS, const KnownBits &RHS) {
+KnownBits KnownBits::remGetLowBits(const KnownBits &LHS, const KnownBits &RHS) {
   unsigned BitWidth = LHS.getBitWidth();
+  if (!RHS.isZero() && RHS.Zero[0]) {
+    // rem X, Y where Y[0:N] is zero will preserve X[0:N] in the result.
+    unsigned RHSZeros = RHS.countMinTrailingZeros();
+    APInt Mask = APInt::getLowBitsSet(BitWidth, RHSZeros);
+    APInt OnesMask = LHS.One & Mask;
+    APInt ZerosMask = LHS.Zero & Mask;
+    return KnownBits(ZerosMask, OnesMask);
+  }
+  return KnownBits(BitWidth);
+}
+
+KnownBits KnownBits::urem(const KnownBits &LHS, const KnownBits &RHS) {
   assert(!LHS.hasConflict() && !RHS.hasConflict());
-  KnownBits Known(BitWidth);
 
+  KnownBits Known = remGetLowBits(LHS, RHS);
   if (RHS.isConstant() && RHS.getConstant().isPowerOf2()) {
     // The upper bits are all zero, the lower ones are unchanged.
+    // NB: Low bits set in `remGetLowBits`.
     APInt LowBits = RHS.getConstant() - 1;
     Known.Zero = LHS.Zero | ~LowBits;
-    Known.One = LHS.One & LowBits;
     return Known;
   }
 
@@ -568,15 +580,14 @@
 }
 
 KnownBits KnownBits::srem(const KnownBits &LHS, const KnownBits &RHS) {
-  unsigned BitWidth = LHS.getBitWidth();
   assert(!LHS.hasConflict() && !RHS.hasConflict());
-  KnownBits Known(BitWidth);
 
+  KnownBits Known = remGetLowBits(LHS, RHS);
   if (RHS.isConstant() && RHS.getConstant().isPowerOf2()) {
     // The low bits of the first operand are unchanged by the srem.
+    // NB: Low bits set in `remGetLowBits`.
     APInt LowBits = RHS.getConstant() - 1;
     Known.Zero = LHS.Zero & LowBits;
-    Known.One = LHS.One & LowBits;
 
     // If the first operand is non-negative or has all low bits zero, then
     // the upper bits are all zero.
diff --git a/llvm/test/Analysis/ValueTracking/knownbits-rem-lowbits.ll b/llvm/test/Analysis/ValueTracking/knownbits-rem-lowbits.ll
--- a/llvm/test/Analysis/ValueTracking/knownbits-rem-lowbits.ll
+++ b/llvm/test/Analysis/ValueTracking/knownbits-rem-lowbits.ll
@@ -3,11 +3,7 @@
 
 define i8 @urem_low_bits_know(i8 %xx, i8 %yy) {
 ; CHECK-LABEL: @urem_low_bits_know(
-; CHECK-NEXT:    [[X:%.*]] = or i8 [[XX:%.*]], 2
-; CHECK-NEXT:    [[Y:%.*]] = and i8 [[YY:%.*]], -4
-; CHECK-NEXT:    [[REM:%.*]] = urem i8 [[X]], [[Y]]
-; CHECK-NEXT:    [[R:%.*]] = and i8 [[REM]], 2
-; CHECK-NEXT:    ret i8 [[R]]
+; CHECK-NEXT:    ret i8 2
 ;
   %x = or i8 %xx, 2
   %y = and i8 %yy, -4
@@ -18,12 +14,7 @@
 
 define i8 @urem_low_bits_know2(i8 %xx, i8 %yy) {
 ; CHECK-LABEL: @urem_low_bits_know2(
-; CHECK-NEXT:    [[XO:%.*]] = and i8 [[XX:%.*]], -4
-; CHECK-NEXT:    [[X:%.*]] = or i8 [[XO]], 2
-; CHECK-NEXT:    [[Y:%.*]] = and i8 [[YY:%.*]], -4
-; CHECK-NEXT:    [[REM:%.*]] = urem i8 [[X]], [[Y]]
-; CHECK-NEXT:    [[R:%.*]] = and i8 [[REM]], 3
-; CHECK-NEXT:    ret i8 [[R]]
+; CHECK-NEXT:    ret i8 2
 ;
   %xo = or i8 %xx, 2
   %x = and i8 %xo, 254
@@ -80,11 +71,7 @@
 
 define i8 @srem_low_bits_know(i8 %xx, i8 %yy) {
 ; CHECK-LABEL: @srem_low_bits_know(
-; CHECK-NEXT:    [[X:%.*]] = or i8 [[XX:%.*]], 10
-; CHECK-NEXT:    [[Y:%.*]] = and i8 [[YY:%.*]], -4
-; CHECK-NEXT:    [[REM:%.*]] = srem i8 [[X]], [[Y]]
-; CHECK-NEXT:    [[R:%.*]] = and i8 [[REM]], 2
-; CHECK-NEXT:    ret i8 [[R]]
+; CHECK-NEXT:    ret i8 2
 ;
   %x = or i8 %xx, 10
   %y = and i8 %yy, -4
@@ -95,11 +82,7 @@
 
 define i8 @srem_low_bits_know2(i8 %xx, i8 %yy) {
 ; CHECK-LABEL: @srem_low_bits_know2(
-; CHECK-NEXT:    [[X:%.*]] = or i8 [[XX:%.*]], 1
-; CHECK-NEXT:    [[Y:%.*]] = and i8 [[YY:%.*]], -2
-; CHECK-NEXT:    [[REM:%.*]] = srem i8 [[X]], [[Y]]
-; CHECK-NEXT:    [[R:%.*]] = and i8 [[REM]], 1
-; CHECK-NEXT:    ret i8 [[R]]
+; CHECK-NEXT:    ret i8 1
 ;
   %x = or i8 %xx, 1
   %y = and i8 %yy, -2
diff --git a/llvm/test/Transforms/LoopVectorize/AArch64/masked-call.ll b/llvm/test/Transforms/LoopVectorize/AArch64/masked-call.ll
--- a/llvm/test/Transforms/LoopVectorize/AArch64/masked-call.ll
+++ b/llvm/test/Transforms/LoopVectorize/AArch64/masked-call.ll
@@ -33,8 +33,7 @@
 ; TFNONE-NEXT:    [[TMP9:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
 ; TFNONE-NEXT:    br i1 [[TMP9]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
 ; TFNONE:       middle.block:
-; TFNONE-NEXT:    [[CMP_N:%.*]] = icmp eq i64 1025, [[N_VEC]]
-; TFNONE-NEXT:    br i1 [[CMP_N]], label [[FOR_COND_CLEANUP:%.*]], label [[SCALAR_PH]]
+; TFNONE-NEXT:    br i1 false, label [[FOR_COND_CLEANUP:%.*]], label [[SCALAR_PH]]
 ; TFNONE:       scalar.ph:
 ; TFNONE-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i64 [ [[N_VEC]], [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY:%.*]] ]
 ; TFNONE-NEXT:    br label [[FOR_BODY:%.*]]
@@ -193,8 +192,7 @@
 ; TFNONE-NEXT:    [[TMP11:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
 ; TFNONE-NEXT:    br i1 [[TMP11]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP4:![0-9]+]]
 ; TFNONE:       middle.block:
-; TFNONE-NEXT:    [[CMP_N:%.*]] = icmp eq i64 1025, [[N_VEC]]
-; TFNONE-NEXT:    br i1 [[CMP_N]], label [[FOR_COND_CLEANUP:%.*]], label [[SCALAR_PH]]
+; TFNONE-NEXT:    br i1 false, label [[FOR_COND_CLEANUP:%.*]], label [[SCALAR_PH]]
 ; TFNONE:       scalar.ph:
 ; TFNONE-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i64 [ [[N_VEC]], [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY:%.*]] ]
 ; TFNONE-NEXT:    br label [[FOR_BODY:%.*]]
@@ -395,8 +393,7 @@
 ; TFNONE-NEXT:    [[TMP12:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
 ; TFNONE-NEXT:    br i1 [[TMP12]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP6:![0-9]+]]
 ; TFNONE:       middle.block:
-; TFNONE-NEXT:    [[CMP_N:%.*]] = icmp eq i64 1025, [[N_VEC]]
-; TFNONE-NEXT:    br i1 [[CMP_N]], label [[FOR_COND_CLEANUP:%.*]], label [[SCALAR_PH]]
+; TFNONE-NEXT:    br i1 false, label [[FOR_COND_CLEANUP:%.*]], label [[SCALAR_PH]]
 ; TFNONE:       scalar.ph:
 ; TFNONE-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i64 [ [[N_VEC]], [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY:%.*]] ]
 ; TFNONE-NEXT:    br label [[FOR_BODY:%.*]]
@@ -607,8 +604,7 @@
 ; TFNONE-NEXT:    [[TMP9:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
 ; TFNONE-NEXT:    br i1 [[TMP9]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP8:![0-9]+]]
 ; TFNONE:       middle.block:
-; TFNONE-NEXT:    [[CMP_N:%.*]] = icmp eq i64 1025, [[N_VEC]]
-; TFNONE-NEXT:    br i1 [[CMP_N]], label [[FOR_COND_CLEANUP:%.*]], label [[SCALAR_PH]]
+; TFNONE-NEXT:    br i1 false, label [[FOR_COND_CLEANUP:%.*]], label [[SCALAR_PH]]
 ; TFNONE:       scalar.ph:
 ; TFNONE-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i64 [ [[N_VEC]], [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY:%.*]] ]
 ; TFNONE-NEXT:    br label [[FOR_BODY:%.*]]
@@ -666,8 +662,7 @@
 ; TFFALLBACK-NEXT:    [[TMP9:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
 ; TFFALLBACK-NEXT:    br i1 [[TMP9]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP8:![0-9]+]]
 ; TFFALLBACK:       middle.block:
-; TFFALLBACK-NEXT:    [[CMP_N:%.*]] = icmp eq i64 1025, [[N_VEC]]
-; TFFALLBACK-NEXT:    br i1 [[CMP_N]], label [[FOR_COND_CLEANUP:%.*]], label [[SCALAR_PH]]
+; TFFALLBACK-NEXT:    br i1 false, label [[FOR_COND_CLEANUP:%.*]], label [[SCALAR_PH]]
 ; TFFALLBACK:       scalar.ph:
 ; TFFALLBACK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i64 [ [[N_VEC]], [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY:%.*]] ]
 ; TFFALLBACK-NEXT:    br label [[FOR_BODY:%.*]]
@@ -731,8 +726,7 @@
 ; TFNONE-NEXT:    [[TMP9:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
 ; TFNONE-NEXT:    br i1 [[TMP9]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP10:![0-9]+]]
 ; TFNONE:       middle.block:
-; TFNONE-NEXT:    [[CMP_N:%.*]] = icmp eq i64 1025, [[N_VEC]]
-; TFNONE-NEXT:    br i1 [[CMP_N]], label [[FOR_COND_CLEANUP:%.*]], label [[SCALAR_PH]]
+; TFNONE-NEXT:    br i1 false, label [[FOR_COND_CLEANUP:%.*]], label [[SCALAR_PH]]
 ; TFNONE:       scalar.ph:
 ; TFNONE-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i64 [ [[N_VEC]], [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY:%.*]] ]
 ; TFNONE-NEXT:    br label [[FOR_BODY:%.*]]