[lldb-dev] Question about IRForTarget

Zachary Turner zturner at google.com
Mon Mar 16 10:45:20 PDT 2015

So assuming the correct type is passed today, is that semantically
equivalent to passing nullptr today?  Because if not, then I would have
expected a test to fail somewhere.  Not because an assertion fired, but
because something somewhere had the wrong idea about a type.

On Mon, Mar 16, 2015 at 10:43 AM David Blaikie <blaikie at google.com> wrote:

> On Mon, Mar 16, 2015 at 10:39 AM, Zachary Turner <zturner at google.com>
> wrote:
>> Hi Sean,
>> A change went in over the weekend to change the
>> way GetElementPtrInst::Create works.  Now, for pointer types, you need to
>> manually specify the type of the pointee, as pointerType->getType() won't
>> work anymore.  This broke the build, so a workaround was employed to simply
>> pass nullptr for this argument.  But this is likely to be incorrect, and
>> instead we need the actual llvm::Type for the pointee.  I've looked over
>> the code, and I *think* that on line 2209 we can replace the nullptr with
>> old_constant->getType(), and on line 2396 we can place the nullptr with
>> value->getType().
>> What are your thoughts here?
>> Secondly, the change to nullptr does not seem to have caused any test
>> failures.
> This is expected - for now, nullptr is an acceptable value. The assertion
> I have in GetElementPtrInst's ctor is:
> assert(!PointeeType || PointeeType == getSourceElementType());
> Eventually I'll need to remove the nullptr case once I believe I've
> flushed out all the callers - this will verify that the callers are passing
> the type that matches the pointee type of the pointer operand. (at this
> point the current lldb code will assert-fail, if it is tested) You can try
> removing the first part of that assert locally to see if the LLDB code path
> is tested currently.
> Once similar changes have been applied to all pointer-element-type-aware
> uses of pointers in LLVM IR, I'll start trying to remove the ability to
> query a pointer type for its element type.
>> Is there any way we can add some tests for this?  If this is not
>> something that is testable through the public interface, I recently added
>> gtest unit tests to the build.  It's not enabled in the Xcode build (but
>> will be soon), but if you tell me how to set up a test, call the right
>> function, and what outputs to expect, I can write it.
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