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