[cfe-dev] Crash on conditional operation with address_space pointer

[John McCall via cfe-dev]

> On Aug 3, 2018, at 7:42 PM, Leonard Chan <leonardchan at google.com> wrote:
> Does this mean the check during the BitCast codegen shouldn't be there
> in the first place?

We should not be generating code for this program, correct.

John.

> On Fri, Aug 3, 2018 at 4:28 PM John McCall <rjmccall at apple.com> wrote:
>> 
>>> On Aug 3, 2018, at 7:03 PM, Leonard Chan via cfe-dev <cfe-dev at lists.llvm.org> wrote:
>>> Compiling the following causes clang to crash
>>> 
>>> char *cmp(__attribute__((address_space(1))) char *x,
>>> __attribute__((address_space(2))) char *y) {
>>> return x < y ? x : y;
>>> }
>>> 
>>> with the message: "wrong cast for pointers in different address
>>> spaces(must be an address space cast)!"
>>> 
>>> The problem seems to be that BitCast is used when
>>> AddressSpaceConversion should be used instead when casting the `y` to
>>> a void *. The error is thrown during code gen where a BitCast expects
>>> the source and dest address space to be the same.
>>> 
>>> I submitted a patch (https://reviews.llvm.org/D50278) for a fix where
>>> we check for differing address spaces in the operands and perform an
>>> AddressSpaceConversion cast if anyone wants to review it. It seems
>>> that AddressSpaceConversions though were only available when using
>>> OpenCL. I'm not familiar with OpenCL and not sure if this was
>>> intended, but it fixes the crash while still retaining the warning of
>>> using mismatched pointers and all the clang tests pass.
>> 
>> If address spaces 1 and 2 don't overlap — and absent target-specific
>> information, the assumption is that they don't — then neither the comparison
>> nor the conditional operator here should type-check.
>> 
>> John.