[InstCombine] prevent crashing/assert on shift constant expression (PR44028)

The binary operator cast implies an instruction, but the matcher for shift does not:
https://bugs.llvm.org/show_bug.cgi?id=44028

Author: rotateright

llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp

@@ -319,7 +319,8 @@ static Instruction *foldShiftOfShiftedLogic(BinaryOperator &I,
   // TODO: Remove the one-use check if the other logic operand (Y) is constant.
   Value *X, *Y;
   auto matchFirstShift = [&](Value *V) {
-    return match(V, m_OneUse(m_Shift(m_Value(X), m_APInt(C0)))) &&
+    return !isa<ConstantExpr>(V) &&
+           match(V, m_OneUse(m_Shift(m_Value(X), m_APInt(C0)))) &&
            cast<BinaryOperator>(V)->getOpcode() == ShiftOpcode &&
            (*C0 + *C1).ult(Ty->getScalarSizeInBits());
   };

llvm/test/Transforms/InstCombine/shift-logic.ll

@@ -169,3 +169,20 @@ define i32 @lshr_or_extra_use(i32 %x, i32 %y, i32* %p) {
   %sh1 = lshr i32 %r, 7
   ret i32 %sh1
 }
+
+; Avoid crashing on constant expressions.
+
+@g = external global i32
+
+define i32 @PR44028(i32 %x) {
+; CHECK-LABEL: @PR44028(
+; CHECK-NEXT:    [[SH1:%.*]] = ashr exact i32 [[X:%.*]], 16
+; CHECK-NEXT:    [[T0:%.*]] = xor i32 [[SH1]], shl (i32 ptrtoint (i32* @g to i32), i32 16)
+; CHECK-NEXT:    [[T27:%.*]] = ashr exact i32 [[T0]], 16
+; CHECK-NEXT:    ret i32 [[T27]]
+;
+  %sh1 = ashr exact i32 %x, 16
+  %t0 = xor i32 %sh1, shl (i32 ptrtoint (i32* @g to i32), i32 16)
+  %t27 = ashr exact i32 %t0, 16
+  ret i32 %t27
+}