[GPUCC] how to remove _ZL21__nvvm_reflect_anchorv() automatically?

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#1

Hi,

I needed to compile a cuda source file (say, a.cu) into IR (a.bc), and then merge a.bc with another bitcode file (b.bc, compiled from b.cu). So I used llvm-link a.bc b.bc -o c.bc

However, I noticed that an internal function ’ _ZL21__nvvm_reflect_anchorv() ’ is defined in both a.bc & b.bc, and when merging these two files, one of the two definitions was renamed to ‘_ZL21__nvvm_reflect_anchorv.2()’, and written into c.bc.

Then I did llc c.bc -o c.s -march=nvptx ; ptxas c.s -o c.o

However, ptxas would give the following complaint:

ptxas c.s, line 171; error : Duplicate definition of function ‘_ZL21__nvvm_reflect_anchorv’

ptxas c.s, line 171; fatal : Parsing error near ‘.2’: syntax error

So I inspected c.s and found the issue above was caused by the following line:

.func (.param .b32 func_retval0) _ZL21__nvvm_reflect_anchorv.2() // @_ZL21__nvvm_reflect_anchorv.2

After I manually deleted the definition of this function in c.s, the compilation works file. I wonder how could I force llc to remove **_ZL21__nvvm_reflect_anchorv.2**()? Or is that possible to prevent _ZL21__nvvm_reflect_anchorv**()** from being generated into a.bc & b.bc in the first place? Or is this possible to ask llvm-link to NOT rename _ZL21__nvvm_reflect_anchorv() into ZL21__nvvm_reflect_anchorv**.2****()**?

Thanks!

Yuanfeng Peng

#2

The actual problem here is that PTX appears to not allow ‘.’ in symbol names. We should probably just change our PTX emission to mangle dots somehow.

#3

Yeah, ‘.’ is the direct reason for the ptxas failure here. I’m curious, however, about what the purpose of nvvm_reflect_anchorv() is here, and why does the front-end always generate this function? Since the current PTX emission doesn’t mangle dots, it would be a reasonable workaround for me to prevent the front-end from generating this function in the first place. Is there any magic option available to do so?

Thanks!
yuanfeng

#4

Artem,

With David’s http://reviews.llvm.org/rL265060, do you think __nvvm_reflect_anchor is still necessary?

#5

David’s change makes nvvm_reflect_anchor unnecessary. The issue with dots in names generated by llvm still needs to be fixed.

#6

r267062 removed __nvvm_reflect_anchor() so you should no longer see this particular manifestation of illegal-character-in-PTX problem.

–Artem

#7

Awesome! Thanks for letting me know, Artem!

yuanfeng