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103 lines
3.3 KiB
ReStructuredText
103 lines
3.3 KiB
ReStructuredText
==================================================
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How To Add A Constrained Floating-Point Intrinsic
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==================================================
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.. contents::
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:local:
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.. warning::
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This is a work in progress.
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Add the intrinsic
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=================
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Multiple files need to be updated when adding a new constrained intrinsic.
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Add the new intrinsic to the table of intrinsics.::
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include/llvm/IR/Intrinsics.td
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Update class ConstrainedFPIntrinsic to know about the intrinsics.::
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include/llvm/IR/IntrinsicInst.h
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Functions like ConstrainedFPIntrinsic::isUnaryOp() or
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ConstrainedFPIntrinsic::isTernaryOp() may need to know about the new
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intrinsic.::
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lib/IR/IntrinsicInst.cpp
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Update the IR verifier::
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lib/IR/Verifier.cpp
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Add SelectionDAG node types
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===========================
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Add the new STRICT version of the node type to the ISD::NodeType enum.::
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include/llvm/CodeGen/ISDOpcodes.h
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In class SDNode update isStrictFPOpcode()::
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include/llvm/CodeGen/SelectionDAGNodes.h
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A mapping from the STRICT SDnode type to the non-STRICT is done in
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TargetLoweringBase::getStrictFPOperationAction(). This allows STRICT
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nodes to be legalized similarly to the non-STRICT node type.::
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include/llvm/CodeGen/TargetLowering.h
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Building the SelectionDAG
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-------------------------
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The switch statement in SelectionDAGBuilder::visitIntrinsicCall() needs
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to be updated to call SelectionDAGBuilder::visitConstrainedFPIntrinsic().
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That function, in turn, needs to be updated to know how to create the
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SDNode for the intrinsic. The new STRICT node will eventually be converted
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to the matching non-STRICT node. For this reason it should have the same
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operands and values as the non-STRICT version but should also use the chain.
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This makes subsequent sharing of code for STRICT and non-STRICT code paths
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easier.::
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lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
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Most of the STRICT nodes get legalized the same as their matching non-STRICT
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counterparts. A new STRICT node with this property must get added to the
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switch in SelectionDAGLegalize::LegalizeOp().::
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lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
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Other parts of the legalizer may need to be updated as well. Look for
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places where the non-STRICT counterpart is legalized and update as needed.
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Be careful of the chain since STRICT nodes use it but their counterparts
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often don't.
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The code to do the conversion or mutation of the STRICT node to a non-STRICT
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version of the node happens in SelectionDAG::mutateStrictFPToFP(). Be
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careful updating this function since some nodes have the same return type
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as their input operand, but some are different. Both of these cases must
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be properly handled.::
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lib/CodeGen/SelectionDAG/SelectionDAG.cpp
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However, the mutation may not happen if the new node has not been registered
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in TargetLoweringBase::initActions(). If the corresponding non-STRICT node
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is Legal but a target does not know about STRICT nodes then the STRICT
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node will default to Legal and mutation will be bypassed with a "Cannot
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select" error. Register the new STRICT node as Expand to avoid this bug.::
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lib/CodeGen/TargetLoweringBase.cpp
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To make debug logs readable it is helpful to update the SelectionDAG's
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debug logger:::
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lib/CodeGen/SelectionDAG/SelectionDAGDumper.cpp
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Add documentation and tests
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===========================
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::
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docs/LangRef.rst
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