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#include "slang-ir-defer-buffer-load.h"
#include "slang-ir-clone.h"
#include "slang-ir-dominators.h"
#include "slang-ir-insts.h"
#include "slang-ir-redundancy-removal.h"
#include "slang-ir-util.h"
#include "slang-ir.h"
namespace Slang
{
struct DeferBufferLoadContext
{
// Map an original SSA value to a pointer that can be used to load the value.
Dictionary<IRInst*, IRInst*> mapValueToPtr;
// Map an ptr to its loaded value.
Dictionary<IRInst*, IRInst*> mapPtrToValue;
IRFunc* currentFunc = nullptr;
// Ensure that for an original SSA value, we have formed a pointer that can be used to load the
// value.
IRInst* ensurePtr(IRInst* valueInst)
{
IRInst* result = nullptr;
if (mapValueToPtr.tryGetValue(valueInst, result))
return result;
IRBuilder b(valueInst);
b.setInsertBefore(valueInst);
switch (valueInst->getOp())
{
case kIROp_StructuredBufferLoad:
case kIROp_StructuredBufferLoadStatus:
{
result = b.emitRWStructuredBufferGetElementPtr(
valueInst->getOperand(0),
valueInst->getOperand(1));
break;
}
case kIROp_GetElement:
{
auto ptr = ensurePtr(valueInst->getOperand(0));
if (!ptr)
return nullptr;
result = b.emitElementAddress(ptr, valueInst->getOperand(1));
break;
}
case kIROp_FieldExtract:
{
auto ptr = ensurePtr(valueInst->getOperand(0));
if (!ptr)
return nullptr;
result = b.emitFieldAddress(ptr, valueInst->getOperand(1));
break;
}
case kIROp_Load:
result = valueInst->getOperand(0);
break;
}
if (result)
{
mapValueToPtr[valueInst] = result;
}
return result;
}
static bool isImmutableBufferLoad(IRInst* inst)
{
// Note: we cannot defer loads from RWStructuredBuffer because there can be other
// instructions that modify the buffer.
switch (inst->getOp())
{
case kIROp_StructuredBufferLoad:
case kIROp_StructuredBufferLoadStatus:
return true;
case kIROp_Load:
{
auto rootAddr = getRootAddr(inst->getOperand(0));
return isPointerToImmutableLocation(rootAddr);
}
default:
return false;
}
}
// Ensure that for a pointer value, we have created a load instruction to materialize the value.
IRInst* materializePointer(IRBuilder& builder, IRInst* loadInst)
{
auto ptr = ensurePtr(loadInst);
if (!ptr)
return nullptr;
IRInst* result = nullptr;
if (mapPtrToValue.tryGetValue(ptr, result))
return result;
IRAlignedAttr* align = nullptr;
if (auto load = as<IRLoad>(loadInst))
align = load->findAttr<IRAlignedAttr>();
if (!as<IRModuleInst>(ptr->getParent()))
{
setInsertAfterOrdinaryInst(&builder, ptr);
IRType* valueType = tryGetPointedToType(&builder, ptr->getFullType());
result = builder.emitLoad(valueType, ptr, align);
mapPtrToValue[ptr] = result;
}
else
{
setInsertBeforeOrdinaryInst(&builder, loadInst);
IRType* valueType = tryGetPointedToType(&builder, ptr->getFullType());
result = builder.emitLoad(valueType, ptr, align);
// Since we are inserting the load in a local scope, we can't register
// the mapping to the pointer, since the global pointer needs to be
// loaded once per function.
}
return result;
}
static bool isSimpleType(IRInst* type)
{
if (auto modType = as<IRRateQualifiedType>(type))
type = modType->getValueType();
if (as<IRStructType>(type))
return false;
if (as<IRTupleType>(type))
return false;
if (as<IRArrayTypeBase>(type))
return false;
return true;
}
void deferBufferLoadInst(IRBuilder& builder, List<IRInst*>& workList, IRInst* loadInst)
{
// Don't defer the load anymore if the type is simple.
if (isSimpleType(loadInst->getDataType()) || loadInst->findAttr<IRAlignedAttr>())
{
auto materializedVal = materializePointer(builder, loadInst);
loadInst->transferDecorationsTo(materializedVal);
loadInst->replaceUsesWith(materializedVal);
return;
}
// Otherwise, look for all uses and try to defer the load before actual use of the value.
ShortList<IRInst*> pendingWorkList;
bool needMaterialize = false;
traverseUses(
loadInst,
[&](IRUse* use)
{
if (needMaterialize)
return;
auto user = use->getUser();
switch (user->getOp())
{
case kIROp_GetElement:
case kIROp_FieldExtract:
{
auto basePtr = ensurePtr(loadInst);
if (!basePtr)
return;
pendingWorkList.add(user);
}
break;
default:
needMaterialize = true;
return;
}
});
if (needMaterialize)
{
auto val = materializePointer(builder, loadInst);
loadInst->transferDecorationsTo(val);
loadInst->replaceUsesWith(val);
loadInst->removeAndDeallocate();
}
else
{
// Append to worklist in reverse order so we process the uses in natural appearance
// order.
for (Index i = pendingWorkList.getCount() - 1; i >= 0; i--)
workList.add(pendingWorkList[i]);
}
}
void deferBufferLoadInFunc(IRFunc* func)
{
removeRedundancyInFunc(func, false);
currentFunc = func;
List<IRInst*> workList;
for (auto block : func->getBlocks())
{
for (auto inst : block->getChildren())
{
if (isImmutableBufferLoad(inst))
{
workList.add(inst);
}
}
}
IRBuilder builder(func);
for (Index i = 0; i < workList.getCount(); i++)
{
auto inst = workList[i];
deferBufferLoadInst(builder, workList, inst);
}
}
void deferBufferLoad(IRGlobalValueWithCode* inst)
{
if (auto func = as<IRFunc>(inst))
{
deferBufferLoadInFunc(func);
}
else if (auto generic = as<IRGeneric>(inst))
{
auto inner = findGenericReturnVal(generic);
if (auto innerFunc = as<IRFunc>(inner))
deferBufferLoadInFunc(innerFunc);
}
}
};
void deferBufferLoad(IRModule* module)
{
DeferBufferLoadContext context;
for (auto childInst : module->getGlobalInsts())
{
if (auto code = as<IRGlobalValueWithCode>(childInst))
{
context.deferBufferLoad(code);
}
}
}
} // namespace Slang
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