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// slang-ir-diff-jvp.cpp
#include "slang-ir-diff-jvp.h"
#include "slang-ir.h"
#include "slang-ir-insts.h"
namespace Slang
{
struct JVPDerivativeContext
{
// This type passes over the module and generates
// forward-mode derivative versions of functions
// that are explicitly marked for it.
//
IRModule* module;
// Shared builder state for our derivative passes.
SharedIRBuilder sharedBuilderStorage;
bool processModule()
{
// We start by initializing our shared IR building state,
// since we will re-use that state for any code we
// generate along the way.
//
SharedIRBuilder* sharedBuilder = &sharedBuilderStorage;
sharedBuilder->init(module);
// Run through all the global-level instructions,
// looking for callables.
// Note: We're only processing global callables (IRGlobalValueWithCode)
// for now.
IRBuilder builderStorage(sharedBuilderStorage);
IRBuilder* builder = &builderStorage;
for (auto inst : module->getGlobalInsts())
{
// If the instr is a callable, get all the basic blocks
if (auto callable = as<IRGlobalValueWithCode>(inst))
{
if (isFunctionMarkedForJVP(callable))
{
SLANG_ASSERT(as<IRFunc>(callable));
IRFunc* jvpFunction = emitJVPFunction(&builderStorage, as<IRFunc>(callable));
builder->addJVPDerivativeReferenceDecoration(callable, jvpFunction);
}
}
}
return true;
}
// Checks decorators to see if the function should
// be differentiated (kIROp_JVPDerivativeMarkerDecoration)
//
bool isFunctionMarkedForJVP(IRGlobalValueWithCode* callable)
{
for(auto decoration = callable->getFirstDecoration();
decoration;
decoration = decoration->getNextDecoration())
{
if (decoration->getOp() == kIROp_JVPDerivativeMarkerDecoration)
{
return true;
}
// TODO: Need to remove this decoration or check for
// JVPDerivativeReferenceDecoration to avoid re-generating code.
}
return false;
}
List<IRParam*> emitFuncParameters(IRBuilder* builder, IRFuncType* dataType)
{
List<IRParam*> params;
for(UIndex i = 0; i < dataType->getParamCount(); i++)
{
params.add(
builder->emitParam(dataType->getParamType(i)));
}
return params;
}
// Perform forward-mode automatic differentiation on
// the intstructions.
IRFunc* emitJVPFunction(IRBuilder* builder,
IRFunc* primalFn)
{
// Note (sai): Is this safe? Should we use setInsertInto?
builder->setInsertBefore(primalFn->getNextInst());
auto jvpFn = builder->createFunc();
IRType* jvpFuncType = primalTypeToJVPType(primalFn->getFullType());
jvpFn->setFullType(jvpFuncType);
if (auto jvpName = getJVPFuncName(builder, primalFn))
builder->addNameHintDecoration(jvpFn, jvpName);
builder->setInsertInto(jvpFn);
// Start with _extremely_ basic functions
SLANG_ASSERT(primalFn->getFirstBlock() == primalFn->getLastBlock());
for (auto block = primalFn->getFirstBlock(); block; block = block->getNextBlock())
{
IRBlock* newJVPBlock = nullptr;
if (block == primalFn->getFirstBlock())
{
newJVPBlock = builder->emitBlock();
emitFuncParameters(builder, as<IRFuncType>(jvpFuncType));
}
newJVPBlock = emitJVPBlock(builder, primalFn->getFirstBlock(), newJVPBlock);
}
return jvpFn;
}
IRStringLit* getJVPFuncName(IRBuilder* builder,
IRFunc* func)
{
auto oldLoc = builder->getInsertLoc();
builder->setInsertBefore(func);
IRStringLit* name = nullptr;
if (auto linkageDecoration = func->findDecoration<IRLinkageDecoration>())
{
name = builder->getStringValue((String(linkageDecoration->getMangledName()) + "_jvp").getUnownedSlice());
}
else if (auto namehintDecoration = func->findDecoration<IRNameHintDecoration>())
{
name = builder->getStringValue((String(namehintDecoration->getName()) + "_jvp").getUnownedSlice());
}
builder->setInsertLoc(oldLoc);
return name;
}
IRBlock* emitJVPBlock(IRBuilder* builder,
IRBlock* primalBlock,
IRBlock* jvpBlock = nullptr)
{
// Create if not already provided, and insert into new block.
if (!jvpBlock)
jvpBlock = builder->emitBlock();
else
builder->setInsertInto(jvpBlock);
// Temporarily, we're going to just emit a single return 0 instruction.
for(auto child = primalBlock->getFirstInst(); child; child = child->getNextInst())
{
if (auto returnOp = as<IRReturn>(child))
{
auto zeroVal = builder->getFloatValue(returnOp->getVal()->getDataType(), 0.0);
builder->emitReturn(zeroVal);
}
}
return jvpBlock;
}
IRType* primalTypeToJVPType(IRType* primalType)
{
// Temporarily, we're going to implement the identity transform.
// The return type is the same as the primal type.
return primalType;
}
};
// Set up context and call main process method.
//
bool processJVPDerivativeMarkers(
IRModule* module,
IRJVPDerivativePassOptions const&)
{
JVPDerivativeContext context;
context.module = module;
return context.processModule();
}
}
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