Index: lib/CodeGen/CGExpr.cpp
===================================================================
--- lib/CodeGen/CGExpr.cpp
+++ lib/CodeGen/CGExpr.cpp
@@ -1302,7 +1302,8 @@
 }
 
 bool CodeGenFunction::EmitScalarRangeCheck(llvm::Value *Value, QualType Ty,
-                                           SourceLocation Loc) {
+                                           SourceLocation Loc,
+                                           Optional<unsigned> BitWidth) {
   bool HasBoolCheck = SanOpts.has(SanitizerKind::Bool);
   bool HasEnumCheck = SanOpts.has(SanitizerKind::Enum);
   if (!HasBoolCheck && !HasEnumCheck)
@@ -1319,9 +1320,32 @@
   if (!getRangeForType(*this, Ty, Min, End, /*StrictEnums=*/true, IsBool))
     return true;
 
+  --End;
+  if (BitWidth) {
+    if (!Min) {
+      // If End > MaxValueForWidth, then Value < End. Skip the range check.
+      auto MaxValueForWidth =
+          llvm::APInt::getMaxValue(*BitWidth).zextOrSelf(End.getBitWidth());
+      if (End.ugt(MaxValueForWidth))
+        return false;
+    } else {
+      assert(Min.eq(-(End + 1)) &&
+             "The full range check assumes Min = -(End + 1)");
+      assert(Ty->hasSignedIntegerRepresentation() &&
+             "The full range check works on signed integers only");
+
+      // If Min < MinValueForWidth, then Value > Min. We know Min = -(End + 1),
+      // so End > MaxValueForWidth, and Value < End. Skip the range check.
+      auto MinValueForWidth =
+          llvm::APInt::getSignedMinValue(*BitWidth).sextOrSelf(
+              End.getBitWidth());
+      if (Min.slt(MinValueForWidth))
+        return false;
+    }
+  }
+
   SanitizerScope SanScope(this);
   llvm::Value *Check;
-  --End;
   if (!Min) {
     Check = Builder.CreateICmpULE(
         Value, llvm::ConstantInt::get(getLLVMContext(), End));
@@ -1566,7 +1590,7 @@
                               "bf.clear");
   }
   Val = Builder.CreateIntCast(Val, ResLTy, Info.IsSigned, "bf.cast");
-  EmitScalarRangeCheck(Val, LV.getType(), Loc);
+  EmitScalarRangeCheck(Val, LV.getType(), Loc, Info.Size);
   return RValue::get(Val);
 }
 
Index: lib/CodeGen/CodeGenFunction.h
===================================================================
--- lib/CodeGen/CodeGenFunction.h
+++ lib/CodeGen/CodeGenFunction.h
@@ -2892,11 +2892,12 @@
   llvm::Value *EmitFromMemory(llvm::Value *Value, QualType Ty);
 
   /// Check if the scalar \p Value is within the valid range for the given
-  /// type \p Ty.
+  /// type \p Ty. If \p BitWidth is provided, it must be the bit width of the
+  /// storage for the scalar.
   ///
-  /// Returns true if a check is needed (even if the range is unknown).
-  bool EmitScalarRangeCheck(llvm::Value *Value, QualType Ty,
-                            SourceLocation Loc);
+  /// Returns true if range metadata for the scalar should be dropped.
+  bool EmitScalarRangeCheck(llvm::Value *Value, QualType Ty, SourceLocation Loc,
+                            Optional<unsigned> BitWidth = None);
 
   /// EmitLoadOfScalar - Load a scalar value from an address, taking
   /// care to appropriately convert from the memory representation to
Index: test/CodeGenCXX/ubsan-bitfields.cpp
===================================================================
--- test/CodeGenCXX/ubsan-bitfields.cpp
+++ test/CodeGenCXX/ubsan-bitfields.cpp
@@ -7,7 +7,9 @@
 };
 
 struct S {
-  E e1 : 10;
+  E e1 : 10; //< Wide enough for the unsigned range check.
+  E e2 : 2; //< Still wide enough, 3 < 2^2.
+  E e3 : 1; //< Not wide enough, 3 > 2^1.
 };
 
 // CHECK-LABEL: define i32 @_Z4loadP1S
@@ -19,3 +21,65 @@
   // CHECK: call void @__ubsan_handle_load_invalid_value
   return s->e1;
 }
+
+// CHECK-LABEL: define i32 @_Z5load2P1S
+E load2(S *s) {
+  // CHECK: [[LOAD:%.*]] = load i16, i16* {{.*}}
+  // CHECK: [[LSHR:%.*]] = lshr i16 [[LOAD]], 10
+  // CHECK: [[CLEAR:%.*]] = and i16 [[LSHR]], 3
+  // CHECK: [[CAST:%.*]] = zext i16 [[CLEAR]] to i32
+  // CHECK: icmp ule i32 [[CAST]], 3, !nosanitize
+  // CHECK: call void @__ubsan_handle_load_invalid_value
+  return s->e2;
+}
+
+// CHECK-LABEL: define i32 @_Z5load3P1S
+E load3(S *s) {
+  // CHECK-NOT: !nosanitize
+  return s->e3;
+}
+
+enum E2 {
+  x = -3,
+  y = 3
+};
+
+struct S2 {
+  E2 e1 : 4; //< Wide enough for signed range checks.
+  E2 e2 : 3; //< Still wide enough, -3 > -2^2 and 3 < 2^2.
+  E2 e3 : 2; //< Not wide enough, -3 < -2^1.
+};
+
+// CHECK-LABEL: define i32 @_Z5load4P2S2
+E2 load4(S2 *s) {
+  // CHECK: [[LOAD:%.*]] = load i16, i16* {{.*}}
+  // CHECK: [[SHL:%.*]] = shl i16 [[LOAD]], 12
+  // CHECK: [[ASHR:%.*]] = ashr i16 [[SHL]], 12
+  // CHECK: [[CAST:%.*]] = sext i16 [[ASHR]] to i32
+  // CHECK: [[UPPER_BOUND:%.*]] = icmp sle i32 [[CAST]], 3, !nosanitize
+  // CHECK: [[LOWER_BOUND:%.*]] = icmp sge i32 [[CAST]], -4, !nosanitize
+  // CHECK: [[BOUND:%.*]] = and i1 [[UPPER_BOUND]], [[LOWER_BOUND]], !nosanitize
+  // CHECK: br i1 [[BOUND]], {{.*}}, !nosanitize
+  // CHECK: call void @__ubsan_handle_load_invalid_value
+  return s->e1;
+}
+
+// CHECK-LABEL: define i32 @_Z5load5P2S2
+E2 load5(S2 *s) {
+  // CHECK: [[LOAD:%.*]] = load i16, i16* {{.*}}
+  // CHECK: [[SHL:%.*]] = shl i16 [[LOAD]], 9
+  // CHECK: [[ASHR:%.*]] = ashr i16 [[SHL]], 13
+  // CHECK: [[CAST:%.*]] = sext i16 [[ASHR]] to i32
+  // CHECK: [[UPPER_BOUND:%.*]] = icmp sle i32 [[CAST]], 3, !nosanitize
+  // CHECK: [[LOWER_BOUND:%.*]] = icmp sge i32 [[CAST]], -4, !nosanitize
+  // CHECK: [[BOUND:%.*]] = and i1 [[UPPER_BOUND]], [[LOWER_BOUND]], !nosanitize
+  // CHECK: br i1 [[BOUND]], {{.*}}, !nosanitize
+  // CHECK: call void @__ubsan_handle_load_invalid_value
+  return s->e2;
+}
+
+// CHECK-LABEL: define i32 @_Z5load6P2S2
+E2 load6(S2 *s) {
+  // CHECK-NOT: !nosanitize
+  return s->e3;
+}