[LLVMdev] Problem with PTX assembly printing (NVPTX backend)

[Justin Holewinski]

Alright, couple of points here:

1. Address space 0 is invalid for global variables.  This is causing a
crash in llc where we use llvm_unreachable() on this case.  This is most
likely why you're seeing llc run forever.  The fix for this is to use
address space 1 for globals, which puts them into PTX global memory.  On
our side, we should provide a meaningful error message in this case.

2. The stdio.h header you're using has no chance of producing IR that is
valid for NVPTX.  In this case, printf gets translated into a call to
puts(), which will be undefined if you try to execute the PTX.

I'm putting together some documentation on using the back-end; hopefully
I'll have something ready soon.


On Mon, Feb 4, 2013 at 2:04 PM, <nkavv at physics.auth.gr> wrote:

> Hi,
>
>
>  Can you post the llc command line you're using?  Can you post an LLVM IR
>> file that causes this behavior?
>>
>
> yes:
>
> ${LLVM_PATH}/bin/llc -o helloworld.s -march=nvptx helloworld.ll
>
> where LLVM_PATH my local installation path for LLVM.
>
> Also attaching helloworld.c:
>
> #include <stdio.h>
>
> int main(void) {
>   printf("Hello World!\n");
>   return 0;
> }
>
>
>
> and helloworld.ll:
>
> ; ModuleID = 'helloworld.c'
> target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-**
> i16:16:16-i32:32:32-i64:64:64-**f32:32:32-f64:64:64-f80:128:**
> 128-v64:64:64-v128:128:128-a0:**0:64-f80:32:32-n8:16:32-S32"
> target triple = "i686-w64-mingw32"
>
> @str = private unnamed_addr constant [13 x i8] c"Hello World!\00"
>
> define i32 @main() nounwind {
>   %puts = tail call i32 @puts(i8* getelementptr inbounds ([13 x i8]* @str,
> i32 0, i32 0))
>   ret i32 0
> }
>
> declare i32 @puts(i8* nocapture) nounwind
>
>
> For instance, the "mips" target produces this:
>
>         .section .mdebug.abi32
>         .previous
>         .file   "helloworld.ll"
>         .text
>         .globl  main
>         .align  2
>         .type   main, at function
>         .set    nomips16                # @main
>         .ent    main
> main:
>         .frame  $sp,24,$ra
>         .mask   0x80000000,-4
>         .fmask  0x00000000,0
>         .set    noreorder
>         .set    nomacro
>         .set    noat
> # BB#0:
>         lui     $2, %hi(_gp_disp)
>         addiu   $2, $2, %lo(_gp_disp)
>         addiu   $sp, $sp, -24
>         sw      $ra, 20($sp)            # 4-byte Folded Spill
>         addu    $gp, $2, $25
>         lw      $1, %got($str)($gp)
>         lw      $25, %call16(puts)($gp)
>         jalr    $25
>         addiu   $4, $1, %lo($str)
>         addiu   $2, $zero, 0
>         lw      $ra, 20($sp)            # 4-byte Folded Reload
>         jr      $ra
>         addiu   $sp, $sp, 24
>         .set    at
>         .set    macro
>         .set    reorder
>         .end    main
> $tmp2:
>         .size   main, ($tmp2)-main
>
>         .type   $str, at object            # @str
>         .section        .rodata.str1.4,"aMS",@**progbits,1
>         .align  2
> $str:
>         .asciz   "Hello World!"
>         .size   $str, 13
>
>
>
>
>
> Best regards
> Nikolaos Kavvadias
>
>
>   BTW I've built LLVM with mingw (strange mixture of gcc-3.4.5 and
>>>
>>>> g++-4.6.1). Native compilation, MIPS backend and other things that i've
>>>>> tested, all work properly.
>>>>>
>>>>>
>>>> Perhaps this "strange mixture" is causing some symbol errors somewhere.
>>>> Can you post the exact sequence of steps you used to build LLVM, along
>>>> with
>>>> the llc command-line that fails for you?
>>>>
>>>>
>>> My configuration options were:
>>>
>>> --prefix=/my/local/path/or/so --enable-shared --enable-targets=all
>>> --enable-optimized --disable-libffi --disable-debug-runtime
>>> --disable-assertions --disable-expensive-checks
>>>
>>> Following configuration i did the typical make and make install (to a
>>> selected path by --prefix.
>>>
>>>
>>> Best regards
>>> Nikolaos Kavvadias
>>>
>>>
>>>
>>>
>>>>
>>>>  Any help is appreciated.
>>>>>
>>>>> Best regards,
>>>>> Nikolaos Kavvadias
>>>>>
>>>>>
>>>>>
>>>>> ______________________________******_________________
>>>>>
>>>>>
>>>>> LLVM Developers mailing list
>>>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>>>> http://lists.cs.uiuc.edu/******mailman/listinfo/llvmdev<http://lists.cs.uiuc.edu/****mailman/listinfo/llvmdev>
>>>>> <http:**//lists.cs.uiuc.edu/**mailman/**listinfo/llvmdev<http://lists.cs.uiuc.edu/**mailman/listinfo/llvmdev>
>>>>> >
>>>>> <http:**//lists.cs.uiuc.edu/**mailman/**listinfo/llvmdev<http://lists.cs.uiuc.edu/mailman/**listinfo/llvmdev>
>>>>> <htt**p://lists.cs.uiuc.edu/mailman/**listinfo/llvmdev<http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev>
>>>>> >
>>>>> >
>>>>>
>>>>>
>>>>>
>>>>
>>>> --
>>>>
>>>> Thanks,
>>>>
>>>> Justin Holewinski
>>>>
>>>>
>>>>
>>>
>>>
>>>
>>
>> --
>>
>> Thanks,
>>
>> Justin Holewinski
>>
>>
>
>


-- 

Thanks,

Justin Holewinski
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