In D62739#1543438, @arsenm wrote:

In D62739#1536428, @b-sumner wrote:

We need to communicate with anyone generating IR to ensure this is being generated before we change the default. clang is only one of those generators. This change will also need to be documented in the usage document.

The planned change is to make the backend more conservative, so it shouldn't break other frontends

We need to communicate with anyone generating IR to ensure this is being generated before we change the default. clang is only one of those generators. This change will also need to be documented in the usage document.

Looks good to me.

Maybe there are already other types like this, but it saddens me that an offline compiled code object could potentially not work properly if the application is using any of these types. Or should the runtime try to detect a problem using argument metadata?

I think it is perfectly reasonable to treat these as essentially relaxed-only atomic RMW operations and require the application to use fences or barriers if necessary. The ordering and scope are only needed if we ever need this operation to act as a non-relaxed atomic RMW.

Actually the conversions don't need non-default-rounded operations, nor are they required by OpenCL. However, we've had requests to implement functions such as add_rtz(x,y) which computes x+y with round-to-zero rounding. Our competitors offer such functions, and we implemented them for HSAIL. So we are really trying to get back to parity with HSAIL.

One thing we've wanted for compute for quite a while now is a way to request non-default-rounded add, sub, mul, div, fma, and sqrt. Assuming we ever figure out how to represent these in the IR, ideally without falling back on intrinsics, could this approach be used to implement and minimize the mode changes for those as well?

Ping. There's quite a bit of interest in getting this exposed by clang.

This approach seems fine to me.

In D49146#1157800, @FarhanaAleen wrote:

By the way, since types are being mixed, shouldn't the summary say something like optimize fma((float)S0.x, (float)S1.x, fma((float)S0.y, (float)S1.y, S2)) --> fdot2(S0, S1, S2)? We only want this transformation if S0 and S1 are <2 x f16>.

Current pattern matching does not support float element type yet, it will be supported next.

You are right, there is a typo in the summary. It should be:
fma((f16)S0.x, (f16)S1.x fma((f16)S0.y, (f16)S1.y, (f16)z)) -> ftrunc(fdot2(S0, S1, (f32)z))

By the way, since types are being mixed, shouldn't the summary say something like optimize fma((float)S0.x, (float)S1.x, fma((float)S0.y, (float)S1.y, S2)) --> fdot2(S0, S1, S2)? We only want this transformation if S0 and S1 are <2 x f16>.

This operation only rounds a single time, and unfortunately always flushes f32 denorms. Thus this transformation should only be done when unsafe math is requested.

Thanks, looks good.

LGTM

Looks good to me.

Thanks! Looks good to me.

LGTM

LGTM, but I'd rather use '+' instead of ',' for the features.

In D39739#1045611, @ashi1 wrote:

Is first one encountered a poor design?

Looks fine to me.

Looks good to me.

In D42711#993438, @yaxunl wrote:

In D42711#992555, @arsenm wrote:

In D42711#992517, @yaxunl wrote:

I think the purpose of this patch is to get a similar usage of clang as nvptx when compiling CUDA, i.e., using cuda as OS instead of using amdhsa as OS and amdgiz as environment. This is more convenient for CUDA application developers since they just need to swap nvptx with amdgcn.

This is a frontend driver question at most. The backend shouldn't need to be aware of this

There are various places in clang where selection is done based on OS==CUDA. If we don't use that OS, we need more complex logic in clang for such choices. I can try making changes to clang to make it work, but I suspect there may be places using OS==CUDA is necessary since it may be needed before parsing the language options.

As I understand it, the option users pass to clang++ is --cuda-gpu-arch=<Arch>. Can't we arrange to generate the right triple if they use gfx900 or some other AMD target name for <Arch>?

In D42711#992503, @arsenm wrote:

You're using this just as an alias for AMDHSAOS. We shouldn't add something that behaves exactly the same

Should we expect that the last 3 arguments have any effect? Do we want to test to ensure they have the expected effects?

In D41699#990909, @b-sumner wrote:

I believe there are 20 distinct samplers. I'd be more comfortable with this if you could arrange that __translate_sampler_initializer would be called with values in [0, 19] instead of [133, 322].

I believe there are 20 distinct samplers. I'd be more comfortable with this if you could arrange that __translate_sampler_initializer would be called with values in [0, 19] instead of [133, 322].

Can this be tested?

Were you going to add min and max separately?

Looks good to me...

Do we need tests for 64-bit atomic loads? Do we need tests for cases where we get buffer instead of flat instructions?

Do we need tests of 64 bit atomic loads? What about cases where we get buffer instructions rather than flat instructions?

Do we need tests of 64-bit atomic loads? Do we need tests where we should have buffer loads instead of a flat loads?

This will break all existing implementations and is not backwards compatible. Is this extra diagnosis really worthwhile? Are developers complaining?

In D41699#971106, @yaxunl wrote:

What's the benefit of this change? Since this change will require all device libraries implementing __translate_sampler_initializer to change accordingly. We need a compelling reason.

The usual rule is to take the first weak definition encountered.

In D40514#938106, @jvesely wrote:

In D40514#937574, @b-sumner wrote:

I suppose if we have some other mechanism to ensure output modifiers are never used, then we could consider running with IEEE=0, but I think we need to continue running with IEEE=1 for compute. There may be users counting on current behavior.

The current behavior is broken for OpenCL so no one should depend on it.

IEEE mode disables output modifiers, which is good since output modifiers are not IEEE compatible and do not support output subnormal values.

Looks good to me.

In D39912#922242, @cfang wrote:

In D39912#922228, @b-sumner wrote:

Pardon my ignorance, but why isn't include/llvm/IR/IntrinsicsAMDGCN.td being updated?

We did not add new intrinsics. We just add support for new data types. In IntrinsicsAMDGCN.td, we have already defined
the data types as any_float which includes half types.

In other wordm llvm.amdgcn.image.load.v4f16 (for example) has already been declared in IntrinsicsAMDGCN.td. And this patch just needs to actually define (implement) it.

Pardon my ignorance, but why isn't include/llvm/IR/IntrinsicsAMDGCN.td being updated?

Pardon my ignorance, but why isn't include/llvm/IR/IntrinsicsAMDGPU.td being updated?

g++4.8.2 is complaining:

This passes my tests, including getting the correct answer for 0.

Looks good to me.

We could potentially update visitCEIL and visitFLOOR as well, and use the same opcode test in each, although I don't think such combinations are very likely.

LGTM. I think we can leave immediates to another patch.

In D37822#877903, @Anastasia wrote:

In D37822#877572, @yaxunl wrote:

In D37822#873876, @Anastasia wrote:

In D37822#872446, @yaxunl wrote:

In D37822#872291, @Anastasia wrote:

Could you please explain a bit more why the alignment have to be put explicitly in the struct? I am just not very convinced this is general enough.

The captured variables are fields of the block literal struct. Due to alignment requirement of these fields, there is alignment requirement of
the block literal struct. The ISA of the block invoke function is generated with the assumption of these alignments. If the block literal is
allocated at a memory address not satisfying the alignment requirement, the kernel behavior is undefined.

Generally, __enqueue_kernel library function needs to prepare the kernel argument before launching the kernel. It usually does this by copying
the block literal to some buffer then pass the address of the buffer to the kernel. Then the address of the buffer has to satisfy the alignment
requirement.

If this block literal struct is not general enough, how about add another field as target reserved size, and leave the remaining space of header for
target specific use. And add a target hook to allow target fill the reserved space, e.g.

struct __opencl_block_literal {
  int total_size;
  int align;
  __generic void *invoke;
  int target_reserved_size; /* round up to 4 bytes */
  int target_reserved[];
  /* captures */
};

I like the idea of the target reserved part actually. But not sure how it could be used without adding any target specific methods?

If we decide to add target reserved fields, I can add target hooks to fill these fields. However I would suggest to leave this for future since I don't see there is need for other fields for now.

I could imagine it can be usefull for some vendor implementations.

However, I am still not clear why the alignment of this struct has to be different from any other struct Clang produces. Normally the alignment of objects have to be known during IR generation to put them correctly in the attributes of generated alloca, store and loads. But as a field inside struct I don't know how it can be useful. I would imagine enqueue_kernel would just operate on the block as if it would be an arbitrary buffer of data. Also would size of the struct not account for any padding to make sure the alignment can be deduced based on it correctly?

enqueue_kernel needs to pass the block struct to the kernel. Let's assume it does this by copying the block struct to a buffer. If enqueue_kernel does not know the alignment of the struct, it can only put it at an arbitrary address in the buffer. Then the kernel has to copy the struct to an aligned private memory and load the fields. However, if the enqueued_kernel knows the alignment of the struct, it can put it at an address satisfying the alignment. Then the kernel can load the fields directly from the buffer, skips the step of copying to an aligned private memory. Therefore, alignment of the block struct is usually a useful information for enqueue_kernel. I think that's why in the SPIRV spec OpEnqueueKernel requires an alignment operand for the block context.

Ok, I just think in C if you use malloc to obtain a pointer to some memory location it doesn't take any alignment information. Then you can use the pointer to copy any data including the struct into the location its pointed to. And the pointer can be used later on correctly. I think the alignment is deduced in this case from the type or the size of an object. Do you know where the alignment information is used for SPIRV call? Also how is the block represented in SPIRV?

Looks good to me.

I'd suggest changing the name to doMemOpsHaveSameBase[Ptr]

The assembler accepts v[N] in addition to vN. I'm not sure if that is needed here.

In D37348#859119, @wdng wrote:

Just add a custom lowering ISD:CTTZ to ISD::CTTZ_ZERO_UNDEF

I think the actual problem is the implementation of ISD::CTTZ not using v_ffbl and not this transformation.

Looks fine to me; I suggested using max since it is faster in many cases.

In D36327#834032, @Anastasia wrote:

In D36327#833891, @yaxunl wrote:

In D36327#833653, @bader wrote:

Hi Sam,

What do you think about implementing this optimization in target specific optimization pass? Since size/alignment is saved as function parameter in LLVM IR, the optimization can be done in target specific components w/o adding additional conditions to generic library.

Thanks,
Alexey

Hi Alexey,

The optimization of the power-of-2 type size is implemented as a library function. Our backend lacks the capability to link in library code at ISA level, so linking of the optimized library function has to be done before any target-specific passes. It seems the only place to do this is Clang codegen since Clang/llvm does not support target-specific pre-linking passes.

My general feeling is that it doesn't look like a generic enough change for the frontend. Even though it is implemented in a generic way, not every target might have a special support for the power of 2 size and also if there is such a support not every implementation would handle it as a library function. But I can see that perhaps LLVM is missing flexibility in the flow to accommodate these needs. Any change we could try to extend the compilation flow such that this target specific optimization could happen before the IR linking?

An update to docs/LangRef.rst is needed.

We don't have a complete replacement yet. We can drop this when the replacement is ready and passing tests.

In D28691#820595, @rjmccall wrote:

In D28691#820541, @b-sumner wrote:

There are other languages for heterogeneous compute that have scopes, although not exposed quite as explicitly as OpenCL. For example AMD's "HC" language. And any language making use of clang and targeting SPIR-V would likely use these builtins. I think a more generic prefix is appropriate, and "scoped" tells us exactly when these are needed.

But would those languages use the same language design for these scopes as OpenCL if they did expose them, as opposed to some more elaborate scoping specification? My objection is not that the concept is inherently OpenCL-specific, it's that the presentation in the language might be inherently OpenCL-specific, which makes staying in the opencl namespace is prudent.

In D28691#820526, @rjmccall wrote:

In D28691#820489, @yaxunl wrote:

In D28691#820466, @b-sumner wrote:

Can we drop the "opencl" part of the name and use something like __scoped_atomic_*? Also, it may not make sense to support non-constant scope here since we can't predict what other scopes may be added by other languages in the future.

we could use the approach of LangAS, i.e. we allow targets to map all language specific scopes to target-specific scope names, since IR only cares about scope names, which are target specific. And this is what the current implementation does.

I have no objection to use the __scoped_atomic_ name. It is more general and extensible. John/Anastasia, any comments? Thanks.

I think I would prefer __opencl_atomic_* until we have some evidence that this concept is more general than just OpenCL.

Can we drop the "opencl" part of the name and use something like __scoped_atomic_*? Also, it may not make sense to support non-constant scope here since we can't predict what other scopes may be added by other languages in the future.

This looks fine to me. I was concerned about how successful we would be pattern matching them.

This patch fixes the broken tests.

mov_dpp should be under the VI+ comment

v_mac_f32 always flushes subnormal inputs just like v_mad_f32

FWIW, rounding controls are needed for llvm.fma.*, llvm.fmuladd.*, and llvm.sqrt.*

clang does not recognize convergent as a valid attribute. There was an attempt to add this, see https://www.mail-archive.com/cfe-commits@lists.llvm.org/msg22271.html but it hasn't had any result. Matt do you see "real uses" for this now?

Looks good to me.

I'd replace argument name AsmPrinter with AP to match the existing style.