[InstCombine] add test for mask op with constant expression; NFC

This is reduced from the post-commit C example in:
afa192cfb6

That was reverted with:
6fedc6a2b4

This will infinite loop unless that transform or the ones
with casts that can "EvaluateInDifferentType" are limited
to ignore constant expressions.

llvm/test/Transforms/InstCombine/constant-expr-datalayout.ll

@@ -1,3 +1,4 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt -passes=instcombine %s -S -o - | FileCheck %s
 
 target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
@@ -6,7 +7,26 @@ target triple = "x86_64-unknown-linux-gnu"
 %test1.struct = type { i32, i32 }
 @test1.aligned_glbl = global %test1.struct zeroinitializer, align 4
 define void @test1(i64 *%ptr) {
+; CHECK-LABEL: @test1(
+; CHECK-NEXT:    store i64 0, i64* [[PTR:%.*]], align 8
+; CHECK-NEXT:    ret void
+;
   store i64 and (i64 ptrtoint (i32* getelementptr (%test1.struct, %test1.struct* @test1.aligned_glbl, i32 0, i32 1) to i64), i64 3), i64* %ptr
-; CHECK: store i64 0, i64* %ptr
   ret void
 }
+
+; Make sure we do not infinite loop trying to convert a constant expression back-and-forth.
+
+@channel_wg4idx = external dso_local constant [9 x i8], align 1
+
+define i64 @OpenFilter(i64 %x) {
+; CHECK-LABEL: @OpenFilter(
+; CHECK-NEXT:    [[T:%.*]] = sub i64 [[X:%.*]], zext (i8 ptrtoint ([9 x i8]* @channel_wg4idx to i8) to i64)
+; CHECK-NEXT:    [[R:%.*]] = and i64 [[T]], 255
+; CHECK-NEXT:    ret i64 [[R]]
+;
+  %sub = sub i64 %x, ptrtoint ([9 x i8]* @channel_wg4idx to i64)
+  %t = trunc i64 %sub to i8
+  %r = zext i8 %t to i64
+  ret i64 %r
+}