diff --git a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
index 89558ee06745c..0bd3ac2bf28a1 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
@@ -988,6 +988,23 @@ Instruction *InstCombinerImpl::visitShl(BinaryOperator &I) {
     return BinaryOperator::CreateLShr(
         ConstantInt::get(Ty, APInt::getSignMask(BitWidth)), X);
 
+  // Try to pre-shift a constant shifted by a variable amount:
+  // C << (X + AddC) --> (C >> -AddC) << X
+  // This requires a no-wrap flag and negative offset constant.
+  const APInt *AddC;
+  if ((I.hasNoSignedWrap() || I.hasNoUnsignedWrap()) &&
+      match(Op0, m_APInt(C)) && match(Op1, m_Add(m_Value(X), m_APInt(AddC))) &&
+      AddC->isNegative() && (-*AddC).ult(BitWidth)) {
+    assert(!C->isZero() && "Expected simplify of shifted zero");
+    unsigned PosOffset = (-*AddC).getZExtValue();
+    if (C->eq(C->lshr(PosOffset).shl(PosOffset))) {
+      Constant *NewC = ConstantInt::get(Ty, C->lshr(PosOffset));
+      Instruction *NewShl = BinaryOperator::CreateShl(NewC, X);
+      NewShl->setHasNoUnsignedWrap(I.hasNoUnsignedWrap());
+      return NewShl;
+    }
+  }
+
   return nullptr;
 }
 
diff --git a/llvm/test/Transforms/InstCombine/shift-add.ll b/llvm/test/Transforms/InstCombine/shift-add.ll
index d1618d92e1e07..98786d924309c 100644
--- a/llvm/test/Transforms/InstCombine/shift-add.ll
+++ b/llvm/test/Transforms/InstCombine/shift-add.ll
@@ -174,8 +174,7 @@ define i32 @shl_add_nsw(i32 %x) {
 
 define i32 @shl_nsw_add_negative(i32 %x) {
 ; CHECK-LABEL: @shl_nsw_add_negative(
-; CHECK-NEXT:    [[A:%.*]] = add i32 [[X:%.*]], -1
-; CHECK-NEXT:    [[R:%.*]] = shl nsw i32 2, [[A]]
+; CHECK-NEXT:    [[R:%.*]] = shl i32 1, [[X:%.*]]
 ; CHECK-NEXT:    ret i32 [[R]]
 ;
   %a = add i32 %x, -1
@@ -183,11 +182,14 @@ define i32 @shl_nsw_add_negative(i32 %x) {
   ret i32 %r
 }
 
+; vectors and extra uses are allowed
+; nuw propagates to the new shift
+
 define <2 x i8> @shl_nuw_add_negative_splat_uses(<2 x i8> %x, <2 x i8>* %p) {
 ; CHECK-LABEL: @shl_nuw_add_negative_splat_uses(
 ; CHECK-NEXT:    [[A:%.*]] = add <2 x i8> [[X:%.*]], <i8 -2, i8 -2>
 ; CHECK-NEXT:    store <2 x i8> [[A]], <2 x i8>* [[P:%.*]], align 2
-; CHECK-NEXT:    [[R:%.*]] = shl nuw <2 x i8> <i8 12, i8 12>, [[A]]
+; CHECK-NEXT:    [[R:%.*]] = shl nuw <2 x i8> <i8 3, i8 3>, [[X]]
 ; CHECK-NEXT:    ret <2 x i8> [[R]]
 ;
   %a = add <2 x i8> %x, <i8 -2, i8 -2>
@@ -196,6 +198,8 @@ define <2 x i8> @shl_nuw_add_negative_splat_uses(<2 x i8> %x, <2 x i8>* %p) {
   ret <2 x i8> %r
 }
 
+; negative test - shift constant must have enough trailing zeros to allow the pre-shift
+
 define i32 @shl_nsw_add_negative_invalid_constant(i32 %x) {
 ; CHECK-LABEL: @shl_nsw_add_negative_invalid_constant(
 ; CHECK-NEXT:    [[A:%.*]] = add i32 [[X:%.*]], -2
@@ -207,6 +211,8 @@ define i32 @shl_nsw_add_negative_invalid_constant(i32 %x) {
   ret i32 %r
 }
 
+; negative test - the offset constant must be negative
+
 define i32 @shl_nsw_add_positive_invalid_constant(i32 %x) {
 ; CHECK-LABEL: @shl_nsw_add_positive_invalid_constant(
 ; CHECK-NEXT:    [[A:%.*]] = add i32 [[X:%.*]], 2
@@ -218,6 +224,8 @@ define i32 @shl_nsw_add_positive_invalid_constant(i32 %x) {
   ret i32 %r
 }
 
+; negative test - a large shift must be detected without crashing
+
 define i32 @shl_nsw_add_negative_invalid_constant2(i32 %x) {
 ; CHECK-LABEL: @shl_nsw_add_negative_invalid_constant2(
 ; CHECK-NEXT:    [[A:%.*]] = add i32 [[X:%.*]], -33
@@ -229,6 +237,9 @@ define i32 @shl_nsw_add_negative_invalid_constant2(i32 %x) {
   ret i32 %r
 }
 
+; negative test - currently transformed to 'xor' before we see it,
+; but INT_MIN should be handled too
+
 define i4 @shl_nsw_add_negative_invalid_constant3(i4 %x) {
 ; CHECK-LABEL: @shl_nsw_add_negative_invalid_constant3(
 ; CHECK-NEXT:    [[A:%.*]] = xor i4 [[X:%.*]], -8