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Fix overflow in softmax #82

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Fix overflow in softmax #82

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6 changes: 5 additions & 1 deletion lleaves/compiler/codegen/codegen.py
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Original file line number Diff line number Diff line change
Expand Up @@ -317,6 +317,7 @@ def _populate_objective_func_block(
llvm_copysign = builder.module.declare_intrinsic(
"llvm.copysign", (DTYPE, DTYPE), ir.FunctionType(DTYPE, (DTYPE, DTYPE))
)
llvm_maxnum = builder.module.declare_intrinsic("llvm.maxnum", (DTYPE, DTYPE), ir.FunctionType(DTYPE, (DTYPE, DTYPE)))
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Any reason why you're using maxnum instead of maximum? Sounds like maximum propagates NaNs while maxnum doesn't, and when in doubt I'd probably rather propagate them.

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@starkwj starkwj Aug 1, 2024 •
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Thanks, I agree with you.
However, maximum cannot work for me (and maybe a common case). When I try maximum, It turns out as "LLVM ERROR: Cannot select: t65: f64 = fmaximum t55, t64".
I tried to find out the cause, listed below. I'am not familiar with llvm, so I cannot ensure the below is correct.

  1. The issue is simliar to Cannot select llvm.{min,max}imum.{f32,f64} llvm/llvm-project#53353 . From replies, it seems that maximum of float has been supported not long ago: llvm/llvm-project@a82d27a
  2. For llvmlite, I installed the latest version 0.43.0 by pre-built binary (pip or conda), and the required LLVM is integrated by llvmlite binary (https://llvmlite.readthedocs.io/en/latest/admin-guide/install.html). I believe this is a common usage. The integrated LLVM doesn't seems to support the float version of maximum.

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Huh yeah it seems this is not implement. I guess it doesn't super matter, since we're currently doing this elementwise anyway (instead of e.g. using llvm.vector.reduce.fmax) you could just implement it via fcmp followed by select.


if average_output:
args[0] = builder.fdiv(args[0], get_fdtype_const(num_trees, use_fp64))
Expand Down Expand Up @@ -368,7 +369,10 @@ def _populate_sigmoid(alpha):
elif objective == "multiclass":
assert len(args)
# TODO Might profit from vectorization, needs testing
result = [builder.call(llvm_exp, [arg]) for arg in args]
arg_max = args[0]
for a in args[1:]:
arg_max = builder.call(llvm_maxnum, [arg_max, a])
result = [builder.call(llvm_exp, [builder.fsub(arg, arg_max)]) for arg in args]

denominator = get_fdtype_const(0.0, use_fp64)
for r in result:
Expand Down
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