frasercrmck wrote:
> > So is the sign function currently implemented in the OpenCL headers?
>
> The sign function for SPIR-V/Mesa is currently implemented by libclc
> [here](https://github.com/llvm/llvm-project/blob/main/libclc/generic/lib/common/sign.cl).
> With this change, `sign` now calls `__clc_sign` which has the same
> implementation. We just need to do a bit of extra inlining of CLC functions
> into OpenCL functions to maintain more or less the same SPIR-V.
There are differences in the SPIR-V and I was wondering if you could tell me
whether or not it's okay.
Before:
```
%_Z4signf = OpFunction %float DontInline %13378
%x_52 = OpFunctionParameter %float
%entry_170 = OpLabel
%retval = OpVariable %_ptr_Function_float Function
%x_addr_52 = OpVariable %_ptr_Function_float Function
OpStore %x_addr_52 %x_52 Aligned 4
%14371 = OpLoad %float %x_addr_52 Aligned 4
%14372 = OpIsNan %bool %14371
%call_162 = OpSelect %uint %14372 %uint_1 %uint_0
%tobool = OpINotEqual %bool %call_162 %uint_0
OpBranchConditional %tobool %if_then %if_end
%if_then = OpLabel
OpStore %retval %float_0 Aligned 4
OpBranch %return
%if_end = OpLabel
%14376 = OpLoad %float %x_addr_52 Aligned 4
%cmp_109 = OpFOrdGreaterThan %bool %14376 %float_0
OpBranchConditional %cmp_109 %if_then1 %if_end2
%if_then1 = OpLabel
OpStore %retval %float_1 Aligned 4
OpBranch %return
%if_end2 = OpLabel
%14378 = OpLoad %float %x_addr_52 Aligned 4
%cmp3 = OpFOrdLessThan %bool %14378 %float_0
OpBranchConditional %cmp3 %if_then4 %if_end5
%if_then4 = OpLabel
OpStore %retval %float_n1 Aligned 4
OpBranch %return
%if_end5 = OpLabel
%14381 = OpLoad %float %x_addr_52 Aligned 4
OpStore %retval %14381 Aligned 4
OpBranch %return
%return = OpLabel
%14382 = OpLoad %float %retval Aligned 4
OpReturnValue %14382
OpFunctionEnd
```
```
%_Z4signf = OpFunction %float DontInline %13378
%a_32 = OpFunctionParameter %float
%entry_170 = OpLabel
%retval_i = OpVariable %_ptr_Function_float Function
%x_addr_i = OpVariable %_ptr_Function_float Function
%a_addr_32 = OpVariable %_ptr_Function_float Function
OpStore %a_addr_32 %a_32 Aligned 4
%14372 = OpLoad %float %a_addr_32 Aligned 4
%14373 = OpBitcast %_ptr_Function_uchar %retval_i
OpLifetimeStart %14373 4
%14374 = OpBitcast %_ptr_Function_uchar %x_addr_i
OpLifetimeStart %14374 4
OpStore %x_addr_i %14372 Aligned 4
%14375 = OpLoad %float %x_addr_i Aligned 4
%14376 = OpIsNan %bool %14375
%call_i = OpSelect %uint %14376 %uint_1 %uint_0
%tobool_i = OpINotEqual %bool %call_i %uint_0
OpBranchConditional %tobool_i %if_then_i %if_end_i
%if_then_i = OpLabel
OpStore %retval_i %float_0 Aligned 4
OpBranch %_Z10__clc_signf_exit
%if_end_i = OpLabel
%14380 = OpLoad %float %x_addr_i Aligned 4
%cmp_i = OpFOrdGreaterThan %bool %14380 %float_0
OpBranchConditional %cmp_i %if_then1_i %if_end2_i
%if_then1_i = OpLabel
OpStore %retval_i %float_1 Aligned 4
OpBranch %_Z10__clc_signf_exit
%if_end2_i = OpLabel
%14382 = OpLoad %float %x_addr_i Aligned 4
%cmp3_i = OpFOrdLessThan %bool %14382 %float_0
OpBranchConditional %cmp3_i %if_then4_i %if_end5_i
%if_then4_i = OpLabel
OpStore %retval_i %float_n1 Aligned 4
OpBranch %_Z10__clc_signf_exit
%if_end5_i = OpLabel
%14385 = OpLoad %float %x_addr_i Aligned 4
OpStore %retval_i %14385 Aligned 4
OpBranch %_Z10__clc_signf_exit
%_Z10__clc_signf_exit = OpLabel
%14386 = OpLoad %float %retval_i Aligned 4
%14387 = OpBitcast %_ptr_Function_uchar %retval_i
OpLifetimeStop %14387 4
%14388 = OpBitcast %_ptr_Function_uchar %x_addr_i
OpLifetimeStop %14388 4
OpReturnValue %14386
OpFunctionEnd
```
So it's an extra `alloca` and some lifetime instructions - a result of inlining
unoptimized code. Do you think these will be sufficiently eliminated by the
SPIR-V producer, or should libclc be eliminating these before they reach SPIR-V?
https://github.com/llvm/llvm-project/pull/115699
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