Index: llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
@@ -1239,6 +1239,23 @@
     return BinaryOperator::CreateAnd(Mask, X);
   }
 
+  // Try to pre-shift a constant shifted by a variable amount:
+  // C >> (X - AddC) --> (C << AddC) >> X
+  // This requires a negative offset constant.
+  const APInt *AddC;
+  unsigned BitWidth = Ty->getScalarSizeInBits();
+  if (I.isExact() && 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->shl(PosOffset).lshr(PosOffset))) {
+      Constant *NewC = ConstantInt::get(Ty, C->shl(PosOffset));
+      BinaryOperator *NewLShr = BinaryOperator::CreateLShr(NewC, X);
+      NewLShr->setIsExact();
+      return NewLShr;
+    }
+  }
+
   return nullptr;
 }
 
@@ -1415,6 +1432,24 @@
   if (Instruction *R = foldVariableSignZeroExtensionOfVariableHighBitExtract(I))
     return R;
 
+  // Try to pre-shift a constant shifted by a variable amount:
+  // C >> (X - AddC) --> (C << AddC) >> X
+  // This requires the exact flag and a negative offset constant.
+  const APInt *AddC;
+  const APInt *C;
+  if (I.isExact() && 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->shl(PosOffset).ashr(PosOffset))) {
+      Constant *NewC = ConstantInt::get(Ty, C->shl(PosOffset));
+      BinaryOperator *NewAShr = BinaryOperator::CreateAShr(NewC, X);
+      NewAShr->setIsExact();
+      return NewAShr;
+    }
+  }
+
   // See if we can turn a signed shr into an unsigned shr.
   if (MaskedValueIsZero(Op0, APInt::getSignMask(BitWidth), 0, &I))
     return BinaryOperator::CreateLShr(Op0, Op1);
Index: llvm/test/Transforms/InstCombine/shift-add.ll
===================================================================
--- llvm/test/Transforms/InstCombine/shift-add.ll
+++ llvm/test/Transforms/InstCombine/shift-add.ll
@@ -157,6 +157,72 @@
   ret i32 %r
 }
 
+; Negative offset precondition check for lshr_add_negative_shift_positive
+define i32 @lshr_add_positive_shift_positive(i32 %x) {
+; CHECK-LABEL: @lshr_add_positive_shift_positive(
+; CHECK-NEXT:    [[A:%.*]] = add i32 [[X:%.*]], 1
+; CHECK-NEXT:    [[R:%.*]] = lshr exact i32 2, [[A:%.*]]
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %a = add i32 %x, 1
+  %r = lshr exact i32 2, %a
+  ret i32 %r
+}
+
+; Positive constant precondition check for lshr_add_negative_shift_positive
+define i32 @lshr_add_negative_shift_negative(i32 %x) {
+; CHECK-LABEL: @lshr_add_negative_shift_negative(
+; CHECK-NEXT:    [[A:%.*]] = add i32 [[X:%.*]], -1
+; CHECK-NEXT:    [[R:%.*]] = lshr exact i32 -2, [[A:%.*]]
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %a = add i32 %x, -1
+  %r = lshr exact i32 -2, %a
+  ret i32 %r
+}
+
+define i32 @lshr_add_negative_shift_positive(i32 %x) {
+; CHECK-LABEL: @lshr_add_negative_shift_positive(
+; CHECK-NEXT:    [[R:%.*]] = lshr exact i32 4, [[X:%.*]]
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %a = add i32 %x, -1
+  %r = lshr exact i32 2, %a
+  ret i32 %r
+}
+
+; Precondition check for ashr_exact_add_negative_shift_positive
+define i32 @ashr_exact_add_negative_shift_no_trailing_zeros(i32 %x) {
+; CHECK-LABEL: @ashr_exact_add_negative_shift_no_trailing_zeros(
+; CHECK-NEXT:    [[A:%.*]] = add i32 [[X:%.*]], -1
+; CHECK-NEXT:    [[R:%.*]] = lshr i32 1073741824, [[A:%.*]]
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %a = add i32 %x, -1
+  %r = ashr exact i32 1073741824, %a
+  ret i32 %r
+}
+
+define i32 @ashr_exact_add_negative_shift_negative(i32 %x) {
+; CHECK-LABEL: @ashr_exact_add_negative_shift_negative(
+; CHECK-NEXT:    [[R:%.*]] = ashr exact i32 -4, [[X:%.*]]
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %a = add i32 %x, -1
+  %r = ashr exact i32 -2, %a
+  ret i32 %r
+}
+
+define i32 @ashr_exact_add_negative_shift_positive(i32 %x) {
+; CHECK-LABEL: @ashr_exact_add_negative_shift_positive(
+; CHECK-NEXT:    [[R:%.*]] = lshr i32 4, [[X:%.*]]
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %a = add i32 %x, -1
+  %r = ashr exact i32 2, %a
+  ret i32 %r
+}
+
 ; negative test - must have 'nuw'
 
 define i32 @shl_add_nsw(i32 %x) {