llvm dev - Jan 2012 - [LLVMdev] PTX backend fails instruction selection for load of sext

Loads (on ptx64) with an sext of a computed index operand fail instruction
selection:

LLVM ERROR: Cannot select: 0x7ff01401c210: i64,ch = load 0x10580e820,
0x7ff01401b510, 0x7ff01401b910<LD4[%memref1], sext from i32> [ID=8]
  0x7ff01401b510: i64 = PTXISD::LOAD_PARAM 0x10580e820, 0x7ff01401b410 [ORD=2]
[ID=6]
  0x7ff01401b910: i64 = undef [ORD=4] [ID=3]

This is for code of the form:

  %ptr = gep i64* %base, i32 %offset
  %v = load i64* %ptr

when the offset gets directly inlined into the selection DAG slot of the load
during lowering. If it's managed to be stored off in a vreg or something
first (like if it's common subexpression eliminated with another sext of the
same value to i64 that gets used before), this doesn't happen and codegen
works fine.

The attached trivial ll fails with llc -march=ptx64, and works if either of the
"works" paths is uncommented instead of "breaks".

Any suggestions for where to look would be hugely appreciated. This has crept
out from the closed just in time to bite me before a major paper deadline on
Tuesday.

Thanks.

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On Sun, Jan 15, 2012 at 11:45 PM, Jonathan Ragan-Kelley
<jrk at csail.mit.edu>wrote:
> Loads (on ptx64) with an sext of a computed index operand fail instruction
> selection:
>
> LLVM ERROR: Cannot select: 0x7ff01401c210: i64,ch = load 0x10580e820,
> 0x7ff01401b510, 0x7ff01401b910<LD4[%memref1], sext from i32> [ID=8]
>   0x7ff01401b510: i64 = PTXISD::LOAD_PARAM 0x10580e820, 0x7ff01401b410
> [ORD=2] [ID=6]
>   0x7ff01401b910: i64 = undef [ORD=4] [ID=3]
>
> This is for code of the form:
>
>   %ptr = gep i64* %base, *i32* %offset
>   %v = load i64* %ptr
>
> when the offset gets directly inlined into the selection DAG slot of the
> load during lowering. If it's managed to be stored off in a vreg or
> something first (like if it's common subexpression eliminated with
another
> sext of the same value to i64 that gets used before), this doesn't
happen
> and codegen works fine.
>
> The attached trivial ll fails with llc -march=ptx64, and works if either
> of the "works" paths is uncommented instead of
"breaks".
>
> Any suggestions for where to look would be hugely appreciated. This has
> crept out from the closed just in time to bite me before a major paper
> deadline on Tuesday.
>
FYI: Patch sent to Jonathan.  More "official" fix will be committed
later
this week....

>
> Thanks.
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>

-- 

Thanks,

Justin Holewinski
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