stuart added a comment. In https://reviews.llvm.org/D46015#1078260, @AlexeySotkin wrote:
> In https://reviews.llvm.org/D46015#1078235, @stuart wrote: > > > In https://reviews.llvm.org/D46015#1078217, @AlexeySotkin wrote: > > > > > There should not be need for bitcast. Could give an example ? Thanks. > > > > > > If I have a `write_only` pipe as the argument to `get_pipe_max_packets()`, > > and this uses a single `__get_pipe_num_packets()` function taking a > > `read_only` pipe, we will automatically get a bitcast: > > > > %20 = call i32 bitcast (i32 (%opencl.pipe_ro_t*, i32, i32)* > > @__get_pipe_max_packets to i32 (%opencl.pipe_wo_t*, i32, > > i32)*)(%opencl.pipe_wo_t* %19, i32 4, i32 4) > > > > > Sorry, but I don't quite understand what does `get_pipe_max_packets()`, > **uses** `__get_pipe_num_packets()` mean. Could you clarify? Possibly OpenCL > C source example could help. I mean that without these two separate versions, the call to `__get_pipe_num_packets()` that is emitted can include a bitcast. For example: void foo(read_only pipe int r, write_only pipe int w) { get_pipe_num_packets(w); get_pipe_num_packets(r); } `get_pipe_num_packets(w)` is seen first, causing `i32 @__get_pipe_num_packets(%opencl.pipe_wo_t*, i32, i32)` to be implicitly declared. When the call to `__get_pipe_num_packets()` is emitted, this will be with an autogenerated bitcast from the type of the implicit declaration, i.e. `i32 (%opencl.pipe_wo_t*, i32, i32)*` to the type in the emitted expression, i.e. `i32 (%opencl.pipe_ro_t*, i32, i32)*`. Here is the relevant section of IR: %0 = load %opencl.pipe_wo_t*, %opencl.pipe_wo_t** %w.addr, align 8 %1 = call i32 @__get_pipe_num_packets_ro(%opencl.pipe_wo_t* %0, i32 4, i32 4) %2 = load %opencl.pipe_ro_t*, %opencl.pipe_ro_t** %r.addr, align 8 %3 = call i32 bitcast (i32 (%opencl.pipe_wo_t*, i32, i32)* @__get_pipe_num_packets_ro to i32 (%opencl.pipe_ro_t*, i32, i32)*)(%opencl.pipe_ro_t* %2, i32 4, i32 4) If we swap the two calls to `__get_pipe_num_packets()` in the example above, then the type of the implicit declaration will be `i32 (%opencl.pipe_ro_t*, i32, i32)*` and bitcasts will instead be automatically generated when using `get_pipe_num_packets()` with a `write_only` pipe. It seems especially unfortunate that the type of the implicit declaration varies depending on the access qualifier of the first use. https://reviews.llvm.org/D46015 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
