Index: clang/lib/AST/Interp/ByteCodeExprGen.cpp
===================================================================
--- clang/lib/AST/Interp/ByteCodeExprGen.cpp
+++ clang/lib/AST/Interp/ByteCodeExprGen.cpp
@@ -294,6 +294,10 @@
     return Discard(this->emitBitOr(*T, BO));
   case BO_Xor:
     return Discard(this->emitBitXor(*T, BO));
+  case BO_Shl:
+    return Discard(this->emitShl(*LT, *RT, BO));
+  case BO_Shr:
+    return Discard(this->emitShr(*LT, *RT, BO));
   case BO_LAnd:
   case BO_LOr:
   default:
@@ -608,7 +612,13 @@
   case BO_DivAssign:
   case BO_RemAssign:
   case BO_ShlAssign:
+    if (!this->emitShl(*LT, *RT, E))
+      return false;
+    break;
   case BO_ShrAssign:
+    if (!this->emitShr(*LT, *RT, E))
+      return false;
+    break;
   case BO_AndAssign:
   case BO_XorAssign:
   case BO_OrAssign:
Index: clang/lib/AST/Interp/Interp.h
===================================================================
--- clang/lib/AST/Interp/Interp.h
+++ clang/lib/AST/Interp/Interp.h
@@ -1251,84 +1251,63 @@
 // Shr, Shl
 //===----------------------------------------------------------------------===//
 
-template <PrimType TR, PrimType TL, class T = typename PrimConv<TR>::T>
-unsigned Trunc(InterpState &S, CodePtr OpPC, unsigned Bits, const T &V) {
+template <PrimType NameL, PrimType NameR>
+inline bool Shr(InterpState &S, CodePtr OpPC) {
+  using LT = typename PrimConv<NameL>::T;
+  using RT = typename PrimConv<NameR>::T;
+  const auto &RHS = S.Stk.pop<RT>();
+  const auto &LHS = S.Stk.pop<LT>();
+  const unsigned Bits = LHS.bitWidth();
+
+  if (RHS.isNegative()) {
+    const SourceInfo &Loc = S.Current->getSource(OpPC);
+    S.CCEDiag(Loc, diag::note_constexpr_negative_shift) << RHS.toAPSInt();
+    return false;
+  }
+
   // C++11 [expr.shift]p1: Shift width must be less than the bit width of
   // the shifted type.
-  if (Bits > 1 && V >= T::from(Bits, V.bitWidth())) {
+  if (Bits > 1 && RHS >= RT::from(Bits, RHS.bitWidth())) {
     const Expr *E = S.Current->getExpr(OpPC);
-    const APSInt Val = V.toAPSInt();
+    const APSInt Val = RHS.toAPSInt();
     QualType Ty = E->getType();
     S.CCEDiag(E, diag::note_constexpr_large_shift) << Val << Ty << Bits;
-    return Bits;
-  } else {
-    return static_cast<unsigned>(V);
-  }
-}
-
-template <PrimType TL, PrimType TR, typename T = typename PrimConv<TL>::T>
-inline bool ShiftRight(InterpState &S, CodePtr OpPC, const T &V, unsigned RHS) {
-  if (RHS >= V.bitWidth()) {
-    S.Stk.push<T>(T::from(0, V.bitWidth()));
-  } else {
-    S.Stk.push<T>(T::from(V >> RHS, V.bitWidth()));
-  }
-  return true;
-}
-
-template <PrimType TL, PrimType TR, typename T = typename PrimConv<TL>::T>
-inline bool ShiftLeft(InterpState &S, CodePtr OpPC, const T &V, unsigned RHS) {
-  if (V.isSigned() && !S.getLangOpts().CPlusPlus20) {
-    // C++11 [expr.shift]p2: A signed left shift must have a non-negative
-    // operand, and must not overflow the corresponding unsigned type.
-    // C++2a [expr.shift]p2: E1 << E2 is the unique value congruent to
-    // E1 x 2^E2 module 2^N.
-    if (V.isNegative()) {
-      const Expr *E = S.Current->getExpr(OpPC);
-      S.CCEDiag(E, diag::note_constexpr_lshift_of_negative) << V.toAPSInt();
-    } else if (V.countLeadingZeros() < RHS) {
-      S.CCEDiag(S.Current->getExpr(OpPC), diag::note_constexpr_lshift_discards);
-    }
+    return false;
   }
 
-  if (V.bitWidth() == 1) {
-    S.Stk.push<T>(V);
-  } else if (RHS >= V.bitWidth()) {
-    S.Stk.push<T>(T::from(0, V.bitWidth()));
-  } else {
-    S.Stk.push<T>(T::from(V.toUnsigned() << RHS, V.bitWidth()));
-  }
+  unsigned URHS = static_cast<unsigned>(RHS);
+  S.Stk.push<LT>(LT::from(static_cast<unsigned>(LHS) >> URHS, LHS.bitWidth()));
   return true;
 }
 
-template <PrimType TL, PrimType TR>
-inline bool Shr(InterpState &S, CodePtr OpPC) {
-  const auto &RHS = S.Stk.pop<typename PrimConv<TR>::T>();
-  const auto &LHS = S.Stk.pop<typename PrimConv<TL>::T>();
+template <PrimType NameL, PrimType NameR>
+inline bool Shl(InterpState &S, CodePtr OpPC) {
+  using LT = typename PrimConv<NameL>::T;
+  using RT = typename PrimConv<NameR>::T;
+  const auto &RHS = S.Stk.pop<RT>();
+  const auto &LHS = S.Stk.pop<LT>();
   const unsigned Bits = LHS.bitWidth();
 
-  if (RHS.isSigned() && RHS.isNegative()) {
+  if (RHS.isNegative()) {
     const SourceInfo &Loc = S.Current->getSource(OpPC);
     S.CCEDiag(Loc, diag::note_constexpr_negative_shift) << RHS.toAPSInt();
-    return ShiftLeft<TL, TR>(S, OpPC, LHS, Trunc<TR, TL>(S, OpPC, Bits, -RHS));
-  } else {
-    return ShiftRight<TL, TR>(S, OpPC, LHS, Trunc<TR, TL>(S, OpPC, Bits, RHS));
+    return false;
   }
-}
 
-template <PrimType TL, PrimType TR>
-inline bool Shl(InterpState &S, CodePtr OpPC) {
-  const auto &RHS = S.Stk.pop<typename PrimConv<TR>::T>();
-  const auto &LHS = S.Stk.pop<typename PrimConv<TL>::T>();
-  const unsigned Bits = LHS.bitWidth();
-
-  if (RHS.isSigned() && RHS.isNegative()) {
-    const SourceInfo &Loc = S.Current->getSource(OpPC);
-    S.CCEDiag(Loc, diag::note_constexpr_negative_shift) << RHS.toAPSInt();
-    return ShiftRight<TL, TR>(S, OpPC, LHS, Trunc<TR, TL>(S, OpPC, Bits, -RHS));
-  } else {
-    return ShiftLeft<TL, TR>(S, OpPC, LHS, Trunc<TR, TL>(S, OpPC, Bits, RHS));
+  // C++11 [expr.shift]p1: Shift width must be less than the bit width of
+  // the shifted type.
+  if (Bits > 1 && RHS >= RT::from(Bits, RHS.bitWidth())) {
+    const Expr *E = S.Current->getExpr(OpPC);
+    const APSInt Val = RHS.toAPSInt();
+    QualType Ty = E->getType();
+    S.CCEDiag(E, diag::note_constexpr_large_shift) << Val << Ty << Bits;
+    return false;
   }
+
+  unsigned URHS = static_cast<unsigned>(RHS);
+  S.Stk.push<LT>(LT::from(static_cast<unsigned>(LHS) << URHS, LHS.bitWidth()));
+
+  return true;
 }
 
 //===----------------------------------------------------------------------===//
Index: clang/lib/AST/Interp/Opcodes.td
===================================================================
--- clang/lib/AST/Interp/Opcodes.td
+++ clang/lib/AST/Interp/Opcodes.td
@@ -433,6 +433,16 @@
 def Div  : IntegerOpcode;
 def Divf : FloatOpcode;
 
+def Shl : Opcode {
+  let Types = [IntegerTypeClass, IntegerTypeClass];
+  let HasGroup = 1;
+}
+
+def Shr : Opcode {
+  let Types = [IntegerTypeClass, IntegerTypeClass];
+  let HasGroup = 1;
+}
+
 def BitAnd : IntegerOpcode;
 def BitOr : IntegerOpcode;
 def BitXor : IntegerOpcode;
Index: clang/test/AST/Interp/shifts.cpp
===================================================================
--- /dev/null
+++ clang/test/AST/Interp/shifts.cpp
@@ -0,0 +1,124 @@
+// RUN: %clang_cc1 -fexperimental-new-constant-interpreter -std=c++20 -verify %s
+// RUN: %clang_cc1 -fexperimental-new-constant-interpreter -std=c++17 -verify=cxx17 %s
+// RUN: %clang_cc1 -std=c++20 -verify=ref %s
+// RUN: %clang_cc1 -std=c++17 -verify=ref-cxx17 %s
+
+#define CHAR_BIT (sizeof(char) * 8)
+#define WORD_BIT (sizeof(int) * 8)
+#define INT_MAX (__INT_MAX__)
+#define INT_MIN (~__INT_MAX__)
+
+
+namespace shifts {
+  constexpr void test() { // ref-error {{constexpr function never produces a constant expression}} \
+                          // ref-cxx17-error {{constexpr function never produces a constant expression}}
+
+    char c; // cxx17-warning {{uninitialized variable}} \
+            // ref-cxx17-warning {{uninitialized variable}}
+
+    c = 0 << 0;
+    c = 0 << 1;
+    c = 1 << 0;
+    c = 1 << -0;
+    c = 1 >> -0;
+    c = 1 << -1; // expected-warning {{shift count is negative}} \
+                 // cxx17-warning {{shift count is negative}} \
+                 // ref-warning {{shift count is negative}} \
+                 // ref-note {{negative shift count -1}} \
+                 // ref-cxx17-warning {{shift count is negative}} \
+                 // ref-cxx17-note {{negative shift count -1}}
+
+    c = 1 >> -1; // expected-warning {{shift count is negative}} \
+                 // cxx17-warning {{shift count is negative}} \
+                 // ref-warning {{shift count is negative}} \
+                 // ref-cxx17-warning {{shift count is negative}}
+    c = 1 << (unsigned)-1; // expected-warning {{shift count >= width of type}} \
+                           // FIXME: 'implicit conversion' warning missing in the new interpreter. \
+                           // cxx17-warning {{shift count >= width of type}} \
+                           // ref-warning {{shift count >= width of type}} \
+                           // ref-warning {{implicit conversion}} \
+                           // ref-cxx17-warning {{shift count >= width of type}} \
+                           // ref-cxx17-warning {{implicit conversion}}
+    c = 1 >> (unsigned)-1; // expected-warning {{shift count >= width of type}} \
+                           // cxx17-warning {{shift count >= width of type}} \
+                           // ref-warning {{shift count >= width of type}} \
+                           // ref-cxx17-warning {{shift count >= width of type}}
+    c = 1 << c;
+    c <<= 0;
+    c >>= 0;
+    c <<= 1;
+    c >>= 1;
+    c <<= -1; // expected-warning {{shift count is negative}} \
+              // cxx17-warning {{shift count is negative}} \
+              // ref-warning {{shift count is negative}} \
+              // ref-cxx17-warning {{shift count is negative}}
+    c >>= -1; // expected-warning {{shift count is negative}} \
+              // cxx17-warning {{shift count is negative}} \
+              // ref-warning {{shift count is negative}} \
+              // ref-cxx17-warning {{shift count is negative}}
+    c <<= 999999; // expected-warning {{shift count >= width of type}} \
+                  // cxx17-warning {{shift count >= width of type}} \
+                  // ref-warning {{shift count >= width of type}} \
+                  // ref-cxx17-warning {{shift count >= width of type}}
+    c >>= 999999; // expected-warning {{shift count >= width of type}} \
+                  // cxx17-warning {{shift count >= width of type}} \
+                  // ref-warning {{shift count >= width of type}} \
+                  // ref-cxx17-warning {{shift count >= width of type}}
+    c <<= CHAR_BIT; // expected-warning {{shift count >= width of type}} \
+                    // cxx17-warning {{shift count >= width of type}} \
+                    // ref-warning {{shift count >= width of type}} \
+                    // ref-cxx17-warning {{shift count >= width of type}}
+    c >>= CHAR_BIT; // expected-warning {{shift count >= width of type}} \
+                    // cxx17-warning {{shift count >= width of type}} \
+                    // ref-warning {{shift count >= width of type}} \
+                    // ref-cxx17-warning {{shift count >= width of type}}
+    c <<= CHAR_BIT+1; // expected-warning {{shift count >= width of type}} \
+                      // cxx17-warning {{shift count >= width of type}} \
+                      // ref-warning {{shift count >= width of type}} \
+                      // ref-cxx17-warning {{shift count >= width of type}}
+    c >>= CHAR_BIT+1; // expected-warning {{shift count >= width of type}} \
+                      // cxx17-warning {{shift count >= width of type}} \
+                      // ref-warning {{shift count >= width of type}} \
+                      // ref-cxx17-warning {{shift count >= width of type}}
+    (void)((long)c << CHAR_BIT);
+
+    int i; // cxx17-warning {{uninitialized variable}} \
+           // ref-cxx17-warning {{uninitialized variable}}
+    i = 1 << (WORD_BIT - 2);
+    i = 2 << (WORD_BIT - 1); // cxx17-warning {{bits to represent, but 'int' only has}} \
+                             // ref-cxx17-warning {{bits to represent, but 'int' only has}}
+    i = 1 << (WORD_BIT - 1); // cxx17-warning-not {{sets the sign bit of the shift expression}}
+    i = -1 << (WORD_BIT - 1); // cxx17-warning {{shifting a negative signed value is undefined}} \
+                              // ref-cxx17-warning {{shifting a negative signed value is undefined}}
+    i = -1 << 0; // cxx17-warning {{shifting a negative signed value is undefined}} \
+                 // ref-cxx17-warning {{shifting a negative signed value is undefined}}
+    i = 0 << (WORD_BIT - 1);
+    i = (char)1 << (WORD_BIT - 2);
+
+    unsigned u; // cxx17-warning {{uninitialized variable}} \
+                // ref-cxx17-warning {{uninitialized variable}}
+    u = 1U << (WORD_BIT - 1);
+    u = 5U << (WORD_BIT - 1);
+
+    long long int lli; // cxx17-warning {{uninitialized variable}} \
+                       // ref-cxx17-warning {{uninitialized variable}}
+    lli = INT_MIN << 2; // cxx17-warning {{shifting a negative signed value is undefined}} \
+                        // ref-cxx17-warning {{shifting a negative signed value is undefined}}
+    lli = 1LL << (sizeof(long long) * CHAR_BIT - 2);
+  }
+
+  static_assert(1 << 4 == 16, "");
+  constexpr unsigned m = 2 >> 1;
+  static_assert(m == 1, "");
+  constexpr unsigned char c = 0 << 8;
+  static_assert(c == 0, "");
+  static_assert(true << 1, "");
+  static_assert(1 << (WORD_BIT +1) == 0, "");  // expected-error {{not an integral constant expression}} \
+                                               // expected-note {{>= width of type 'int'}} \
+                                               // cxx17-error {{not an integral constant expression}} \
+                                               // cxx17-note {{>= width of type 'int'}} \
+                                               // ref-error {{not an integral constant expression}} \
+                                               // ref-note {{>= width of type 'int'}} \
+                                               // ref-cxx17-error {{not an integral constant expression}} \
+                                               // ref-cxx17-note {{>= width of type 'int'}}
+};