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Avoid increasing grf pressure

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Vector Aliasing will increase grf pressure. This change is to limit
scalar to vector aliasing to avoid increasing register pressure.
This commit is contained in:
Gu, Junjie
2024-03-17 23:14:32 +00:00
committed by igcbot
parent b95a828e57
commit 9e446543fe
2 changed files with 65 additions and 39 deletions
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97
IGC/Compiler/CISACodeGen/VariableReuseAnalysis.cpp
View File

@ -19,6 +19,7 @@ SPDX-License-Identifier: MIT
using namespace llvm;
using namespace IGC;
using namespace IGC::IGCMD;
namespace
{
@ -98,6 +99,7 @@ char VariableReuseAnalysis::ID = 0;
IGC_INITIALIZE_PASS_BEGIN(VariableReuseAnalysis, "VariableReuseAnalysis",
"VariableReuseAnalysis", false, true)
// IGC_INITIALIZE_PASS_DEPENDENCY(RegisterEstimator)
IGC_INITIALIZE_PASS_DEPENDENCY(MetaDataUtilsWrapper)
IGC_INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
IGC_INITIALIZE_PASS_DEPENDENCY(WIAnalysis)
IGC_INITIALIZE_PASS_DEPENDENCY(LiveVarsAnalysis)
@ -1096,55 +1098,60 @@ void VariableReuseAnalysis::InsertElementAliasing(Function* F)
// VectorAlias=0x1: subvec aliasing for isolated values (getRootValue()=null)
// =0x2: subvec aliasing for both isolated and non-isolated value)
const auto control = (m_pCtx->getVectorCoalescingControl() & 0x3);
// To avoid increasing GRF pressure, skip if F is too large.
// To avoid increasing GRF pressure, skip if F is too large or not an entry
const uint32_t NumBBThreshold = (int)IGC_GET_FLAG_VALUE(VectorAliasBBThreshold);
if (control == 0 || F->size() > NumBBThreshold) {
MetaDataUtils* pMdUtils = getAnalysis<MetaDataUtilsWrapper>().getMetaDataUtils();
if (control == 0 || !isEntryFunc(pMdUtils, F) || F->size() > NumBBThreshold) {
return;
}
for (auto II = inst_begin(F), IE = inst_end(F); II != IE; ++II)
for (auto BI = F->begin(), BE = F->end(); BI != BE; ++BI)
{
Instruction* I = &*II;
if (!m_PatternMatch->NeedInstruction(*I))
continue;
BasicBlock* BB = &*BI;
setSkipScalarAliaser(BB);
for (auto II = BB->begin(), IE = BB->end(); II != IE; ++II)
{
Instruction* I = &*II;
if (!m_PatternMatch->NeedInstruction(*I))
continue;
InsertElementInst* IEI = dyn_cast<InsertElementInst>(I);
if (!IEI)
continue;
InsertElementInst* IEI = dyn_cast<InsertElementInst>(I);
if (!IEI)
continue;
// Two cases for sub-vector aliasing:
// 1. extractFrom: sub-vector is created from a base vector.
// For example:
// given base: int8 b; a sub-vector s (int4) can be:
// s = (int4)(b.s4, b.s5, b.s6, b.s7)
// In this case, 's' becomes a part of 'b'. In LLVM IR,
// there are a chain of extElt and insElt instructions for
// doing so.
// 2. insertTo: sub-vector is used to create a base vector.
// For example:
// given sub-vector int4 s0, s1; int8 vector b is created like:
// b = (int8) (s0, s1)
// In this case, both s0 and s1 become part of b.
// Two cases for sub-vector aliasing:
// 1. extractFrom: sub-vector is created from a base vector.
// For example:
// given base: int8 b; a sub-vector s (int4) can be:
// s = (int4)(b.s4, b.s5, b.s6, b.s7)
// In this case, 's' becomes a part of 'b'. In LLVM IR,
// there are a chain of extElt and insElt instructions for
// doing so.
// 2. insertTo: sub-vector is used to create a base vector.
// For example:
// given sub-vector int4 s0, s1; int8 vector b is created like:
// b = (int8) (s0, s1)
// In this case, both s0 and s1 become part of b.
// Start insertElement pattern from the first InsertElement (one
// with UndefValue. Note that this's also the dessa insElt root.
if (!isa<UndefValue>(IEI->getOperand(0)))
continue;
// Start insertElement pattern from the first InsertElement (one
// with UndefValue. Note that this's also the dessa insElt root.
if (!isa<UndefValue>(IEI->getOperand(0)))
continue;
// First, collect all insertElementInst and extractElementInst.
VecInsEltInfoTy AllIEIs;
if (!getAllInsEltsIfAvailable(IEI, AllIEIs)) {
continue;
}
// First, collect all insertElementInst and extractElementInst.
VecInsEltInfoTy AllIEIs;
if (!getAllInsEltsIfAvailable(IEI, AllIEIs)) {
continue;
}
// Check if this is an extractFrom pattern, if so, add alias.
if (processExtractFrom(AllIEIs)) {
continue;
}
// Check if this is an extractFrom pattern, if so, add alias.
if (processExtractFrom(AllIEIs)) {
continue;
}
// Check if this is an insertTo pattern, if so add alias.
if (processInsertTo(AllIEIs)) {
continue;
// Check if this is an insertTo pattern, if so add alias.
if (processInsertTo(AllIEIs)) {
continue;
}
}
}
}
@ -1294,6 +1301,10 @@ bool VariableReuseAnalysis::processInsertTo(VecInsEltInfoTy& AllIEIs)
(Sub && (i - SubStartIx) != AllIEIs[i].FromVec_eltIx)) {
isSubCandidate = false;
}
if (Elt && Sub == nullptr && isSkipScalarAliaser()) {
// Skip scalar coalescing
isSubCandidate = false;
}
// If Sub == nullptr or NextSub != Sub, this is the last element
// of the current Sub (it is a scalar in case of sub == nullpr).
@ -1561,3 +1572,11 @@ bool VariableReuseAnalysis::checkSubAlign (e_alignment& BaseAlign,
BaseAlign = sub_align;
return true;
}
void VariableReuseAnalysis::setSkipScalarAliaser(llvm::BasicBlock* BB)
{
if (BB->size() > 500)
m_skipScalarAliaser = true;
else
m_skipScalarAliaser = false;
}

7
IGC/Compiler/CISACodeGen/VariableReuseAnalysis.hpp
View File

@ -13,6 +13,7 @@ SPDX-License-Identifier: MIT
#include "Compiler/CISACodeGen/CoalescingEngine.hpp"
#include "Compiler/CISACodeGen/BlockCoalescing.hpp"
#include "common/LLVMWarningsPush.hpp"
#include "Compiler/MetaDataUtilsWrapper.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/IR/Dominators.h"
#include "llvm/ADT/TinyPtrVector.h"
@ -193,6 +194,7 @@ namespace IGC {
virtual void getAnalysisUsage(llvm::AnalysisUsage& AU) const override {
// AU.addRequired<RegisterEstimator>();
AU.setPreservesAll();
AU.addRequired<MetaDataUtilsWrapper>();
AU.addRequired<llvm::DominatorTreeWrapperPass>();
AU.addRequired<WIAnalysis>();
AU.addRequired<LiveVarsAnalysis>();
@ -493,6 +495,11 @@ namespace IGC {
// <V's root, V> into the map. This is a quick check to see if any
// value in a dessa CC has been aliased (either aliaser or aliasee)
Val2ValMapTy m_root2AliasMap;
// For vector aliasing heuristic to prevent possible high-reg pressure
bool m_skipScalarAliaser;
void setSkipScalarAliaser(llvm::BasicBlock* BB);
bool isSkipScalarAliaser() const { return m_skipScalarAliaser; }
};
llvm::FunctionPass* createVariableReuseAnalysisPass();