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Merged
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Sep 25, 2024
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[AMDGPU][StructurizeCFG] Maintain branch MD_prof metadata #109813

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83 changes: 65 additions & 18 deletions llvm/lib/Transforms/Scalar/StructurizeCFG.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,7 @@
#include "llvm/IR/Metadata.h"
#include "llvm/IR/PassManager.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/IR/ProfDataUtils.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/Use.h"
#include "llvm/IR/Value.h"
Expand Down Expand Up @@ -85,7 +86,43 @@ using PhiMap = MapVector<PHINode *, BBValueVector>;
using BB2BBVecMap = MapVector<BasicBlock *, BBVector>;

using BBPhiMap = DenseMap<BasicBlock *, PhiMap>;
using BBPredicates = DenseMap<BasicBlock *, Value *>;

using MaybeCondBranchWeights = std::optional<class CondBranchWeights>;

class CondBranchWeights {
uint32_t TrueWeight;
uint32_t FalseWeight;

CondBranchWeights(uint32_t T, uint32_t F) : TrueWeight(T), FalseWeight(F) {}

public:
static MaybeCondBranchWeights tryParse(const BranchInst &Br) {
assert(Br.isConditional());

uint64_t T, F;
if (!extractBranchWeights(Br, T, F))
return std::nullopt;

return CondBranchWeights(T, F);
}

static void setMetadata(BranchInst &Br,
const MaybeCondBranchWeights &Weights) {
assert(Br.isConditional());
if (!Weights)
return;
uint32_t Arr[] = {Weights->TrueWeight, Weights->FalseWeight};
setBranchWeights(Br, Arr, false);
}

CondBranchWeights invert() const {
return CondBranchWeights{FalseWeight, TrueWeight};
}
};

using ValueWeightPair = std::pair<Value *, MaybeCondBranchWeights>;

using BBPredicates = DenseMap<BasicBlock *, ValueWeightPair>;
using PredMap = DenseMap<BasicBlock *, BBPredicates>;
using BB2BBMap = DenseMap<BasicBlock *, BasicBlock *>;

Expand Down Expand Up @@ -271,7 +308,7 @@ class StructurizeCFG {

void analyzeLoops(RegionNode *N);

Value *buildCondition(BranchInst *Term, unsigned Idx, bool Invert);
ValueWeightPair buildCondition(BranchInst *Term, unsigned Idx, bool Invert);

void gatherPredicates(RegionNode *N);

Expand Down Expand Up @@ -449,16 +486,22 @@ void StructurizeCFG::analyzeLoops(RegionNode *N) {
}

/// Build the condition for one edge
Value *StructurizeCFG::buildCondition(BranchInst *Term, unsigned Idx,
bool Invert) {
ValueWeightPair StructurizeCFG::buildCondition(BranchInst *Term, unsigned Idx,
bool Invert) {
Value *Cond = Invert ? BoolFalse : BoolTrue;
MaybeCondBranchWeights Weights;

if (Term->isConditional()) {
Cond = Term->getCondition();
Weights = CondBranchWeights::tryParse(*Term);

if (Idx != (unsigned)Invert)
if (Idx != (unsigned)Invert) {
Cond = invertCondition(Cond);
if (Weights)
Weights = Weights->invert();
}
}
return Cond;
return {Cond, Weights};
}

/// Analyze the predecessors of each block and build up predicates
Expand Down Expand Up @@ -490,8 +533,8 @@ void StructurizeCFG::gatherPredicates(RegionNode *N) {
if (Visited.count(Other) && !Loops.count(Other) &&
!Pred.count(Other) && !Pred.count(P)) {

Pred[Other] = BoolFalse;
Pred[P] = BoolTrue;
Pred[Other] = {BoolFalse, std::nullopt};
Pred[P] = {BoolTrue, std::nullopt};
continue;
}
}
Expand All @@ -512,9 +555,9 @@ void StructurizeCFG::gatherPredicates(RegionNode *N) {

BasicBlock *Entry = R->getEntry();
if (Visited.count(Entry))
Pred[Entry] = BoolTrue;
Pred[Entry] = {BoolTrue, std::nullopt};
else
LPred[Entry] = BoolFalse;
LPred[Entry] = {BoolFalse, std::nullopt};
}
}
}
Expand Down Expand Up @@ -578,12 +621,14 @@ void StructurizeCFG::insertConditions(bool Loops) {
Dominator.addBlock(Parent);

Value *ParentValue = nullptr;
for (std::pair<BasicBlock *, Value *> BBAndPred : Preds) {
MaybeCondBranchWeights ParentWeights = std::nullopt;
for (std::pair<BasicBlock *, ValueWeightPair> BBAndPred : Preds) {
BasicBlock *BB = BBAndPred.first;
Value *Pred = BBAndPred.second;
auto [Pred, Weight] = BBAndPred.second;

if (BB == Parent) {
ParentValue = Pred;
ParentWeights = Weight;
break;
}
PhiInserter.AddAvailableValue(BB, Pred);
Expand All @@ -592,6 +637,7 @@ void StructurizeCFG::insertConditions(bool Loops) {

if (ParentValue) {
Term->setCondition(ParentValue);
CondBranchWeights::setMetadata(*Term, ParentWeights);
} else {
if (!Dominator.resultIsRememberedBlock())
PhiInserter.AddAvailableValue(Dominator.result(), Default);
Expand All @@ -607,7 +653,7 @@ void StructurizeCFG::simplifyConditions() {
for (auto &I : concat<PredMap::value_type>(Predicates, LoopPreds)) {
auto &Preds = I.second;
for (auto &J : Preds) {
auto &Cond = J.second;
Value *Cond = J.second.first;
Instruction *Inverted;
if (match(Cond, m_Not(m_OneUse(m_Instruction(Inverted)))) &&
!Cond->use_empty()) {
Expand Down Expand Up @@ -904,9 +950,10 @@ void StructurizeCFG::setPrevNode(BasicBlock *BB) {
/// Does BB dominate all the predicates of Node?
bool StructurizeCFG::dominatesPredicates(BasicBlock *BB, RegionNode *Node) {
BBPredicates &Preds = Predicates[Node->getEntry()];
return llvm::all_of(Preds, [&](std::pair<BasicBlock *, Value *> Pred) {
return DT->dominates(BB, Pred.first);
});
return llvm::all_of(Preds,
[&](std::pair<BasicBlock *, ValueWeightPair> Pred) {
return DT->dominates(BB, Pred.first);
});
}

/// Can we predict that this node will always be called?
Expand All @@ -918,9 +965,9 @@ bool StructurizeCFG::isPredictableTrue(RegionNode *Node) {
if (!PrevNode)
return true;

for (std::pair<BasicBlock*, Value*> Pred : Preds) {
for (std::pair<BasicBlock *, ValueWeightPair> Pred : Preds) {
BasicBlock *BB = Pred.first;
Value *V = Pred.second;
Value *V = Pred.second.first;

if (V != BoolTrue)
return false;
Expand Down
8 changes: 6 additions & 2 deletions llvm/test/Transforms/StructurizeCFG/structurizer-keep-perf-md.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@ define amdgpu_ps i32 @if_else(i32 %0) {
; OPT-LABEL: define amdgpu_ps i32 @if_else(
; OPT-SAME: i32 [[TMP0:%.*]]) {
; OPT-NEXT: [[C:%.*]] = icmp ne i32 [[TMP0]], 0
; OPT-NEXT: br i1 [[C]], label %[[FALSE:.*]], label %[[FLOW:.*]]
; OPT-NEXT: br i1 [[C]], label %[[FALSE:.*]], label %[[FLOW:.*]], !prof [[PROF0:![0-9]+]]
; OPT: [[FLOW]]:
; OPT-NEXT: [[TMP2:%.*]] = phi i32 [ 33, %[[FALSE]] ], [ undef, [[TMP1:%.*]] ]
; OPT-NEXT: [[TMP3:%.*]] = phi i1 [ false, %[[FALSE]] ], [ true, [[TMP1]] ]
Expand Down Expand Up @@ -40,7 +40,7 @@ define amdgpu_ps void @loop_if_break(i32 %n) {
; OPT: [[LOOP]]:
; OPT-NEXT: [[I:%.*]] = phi i32 [ [[N]], %[[ENTRY]] ], [ [[TMP0:%.*]], %[[FLOW:.*]] ]
; OPT-NEXT: [[C:%.*]] = icmp ugt i32 [[I]], 0
; OPT-NEXT: br i1 [[C]], label %[[LOOP_BODY:.*]], label %[[FLOW]]
; OPT-NEXT: br i1 [[C]], label %[[LOOP_BODY:.*]], label %[[FLOW]], !prof [[PROF1:![0-9]+]]
; OPT: [[LOOP_BODY]]:
; OPT-NEXT: [[I_NEXT:%.*]] = sub i32 [[I]], 1
; OPT-NEXT: br label %[[FLOW]]
Expand Down Expand Up @@ -70,3 +70,7 @@ exit: ; preds = %loop
attributes #0 = { nocallback nofree nosync nounwind speculatable willreturn memory(none) }

!0 = !{!"branch_weights", i32 1000, i32 1}
;.
; OPT: [[PROF0]] = !{!"branch_weights", i32 1, i32 1000}
; OPT: [[PROF1]] = !{!"branch_weights", i32 1000, i32 1}
;.
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