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[XLA] Support fusion of trivial fusion nodes that only contain a parameter

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instruction.

PiperOrigin-RevId: 257245425
This commit is contained in:
Blake Hechtman 2019-07-09 12:16:18 -07:00 committed by TensorFlower Gardener
parent 1059951b8e
commit 50c6158ee8
1 changed files with 27 additions and 4 deletions
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31
tensorflow/compiler/xla/service/hlo_instructions.cc
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@ -1308,10 +1308,21 @@ void HloFusionInstruction::MergeFusionInstruction(
unfused_instructions.push_back(fused_instruction); unfused_instructions.push_back(fused_instruction);
} }
} }
CHECK(unfused_instructions.front() == cloned_fusion->fused_expression_root());
// If there are no unfused instructions, the fused computation must consist
// only of kParameter instructions. Make the operand of the corresponding
// parameter number the new root.
HloInstruction* unfused_root =
unfused_instructions.empty()
? instruction_to_merge->mutable_operand(
instruction_to_merge->fused_instructions_computation()
->root_instruction()
->parameter_number())
: unfused_instructions.front();
CHECK(unfused_root == cloned_fusion->fused_expression_root() ||
unfused_instructions.empty());
// Replace instruction_to_merge use of 'this' with unfused_root. // Replace instruction_to_merge use of 'this' with unfused_root.
TF_CHECK_OK( TF_CHECK_OK(instruction_to_merge->ReplaceUseWith(this, unfused_root));
instruction_to_merge->ReplaceUseWith(this, unfused_instructions.front()));
// Fuse 'unfused_instructions' into 'this'. // Fuse 'unfused_instructions' into 'this'.
for (auto& instruction : unfused_instructions) { for (auto& instruction : unfused_instructions) {
FuseInstruction(instruction); FuseInstruction(instruction);
@ -1359,7 +1370,16 @@ void HloFusionInstruction::MergeFusionInstructionIntoMultiOutput(
} }
} }
HloInstruction* unfused_root = unfused_instructions.front(); // If there are no unfused instructions, the fused computation must consist
// only of kParameter instructions. Make the operand of the corresponding
// parameter number the new root.
HloInstruction* unfused_root =
unfused_instructions.empty()
? instruction_to_merge->mutable_operand(
instruction_to_merge->fused_instructions_computation()
->root_instruction()
->parameter_number())
: unfused_instructions.front();
TF_CHECK_OK(instruction_to_merge->ReplaceAllUsesWith(unfused_root)); TF_CHECK_OK(instruction_to_merge->ReplaceAllUsesWith(unfused_root));
TF_CHECK_OK( TF_CHECK_OK(
@ -1369,6 +1389,9 @@ void HloFusionInstruction::MergeFusionInstructionIntoMultiOutput(
} }
// Fuse the root instruction and generate multiple outputs. // Fuse the root instruction and generate multiple outputs.
if (unfused_instructions.empty()) {
return;
}
FuseInstructionIntoMultiOutput(unfused_root); FuseInstructionIntoMultiOutput(unfused_root);
TF_CHECK_OK(unfused_root->parent()->RemoveInstruction(unfused_root)); TF_CHECK_OK(unfused_root->parent()->RemoveInstruction(unfused_root));
// The rest instructions are of normal fusing. // The rest instructions are of normal fusing.