I just emailed Chris about this. There are actually several related changes needed:

1. Make Type::Int1Ty, Type::Int8Ty, etc. declared as IntegerType*
   in Type.h instead of Type.h. This will also requires changes in
   Type.cpp to the instantiation macros.
2. Add a ConstantInt::getType() method similar to
   ConstantArray::getType() that returns IntegerType instead of
   defaulting to Value::getType() which returns Type*.
3. Change ConstantInt::get(const Type*, uint64_t Val) -> have an
   IntegerType argument. You must use IntegerType to instantiate a
   ConstantInt.
4. Move getIntegerTypeMask from Type class to IntegerType class and
   rename it getBitMask.
5. Adjust the rest of LLVM for the 4 changes above.

I have already assigned Sheng to do this. I'm assigning this PR to him so
we can track his progress with it.

Re: this:

This is difficult because ConstantInt doesn't actually keep the IntegerType*
internally, nor does it require one on construction, etc. This will probably
cause residual effects throughout LLVM, but it shouldn't be very hard to
clean up.

That's not quite right. ConstantInt is a Constant which is a Value which has
Type. All Values in LLVM have types and ConstantInt isn't an exception. There
are three ways to construct a ConstantInt:

static ConstantInt *get(const Type *Ty, int64_t V);
static inline ConstantInt *getTrue();
static inline ConstantInt *getTrue();

The first requires a Type and item 3 on my list above requires that to change to
IntegerType*. For the other two, the type is Type::Int1Ty.

Sheng: this needs to be your highest priority right now as it is "Phase 2" work.

As Chris suggested, the #​3 will not be done. Because it will cause much change
throughout llvm but get no real benefit.

This is now implemented:

http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20070115/042960.html