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[SROA] Unfold gep of index phi (round 2) #83494

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Mar 4, 2024
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[SROA] Unfold gep of index phi (round 2) #83494

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8cc634c
[SROA] Unfold gep of index phi (round 2)
aeubanks Feb 28, 2024
bfc6589
handle phis with duplicate entries
aeubanks Mar 4, 2024
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115 changes: 76 additions & 39 deletions llvm/lib/Transforms/Scalar/SROA.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3956,11 +3956,11 @@ class AggLoadStoreRewriter : public InstVisitor<AggLoadStoreRewriter, bool> {
return false;
}

// Fold gep (select cond, ptr1, ptr2), idx
// Unfold gep (select cond, ptr1, ptr2), idx
// => select cond, gep(ptr1, idx), gep(ptr2, idx)
// and gep ptr, (select cond, idx1, idx2)
// => select cond, gep(ptr, idx1), gep(ptr, idx2)
bool foldGEPSelect(GetElementPtrInst &GEPI) {
bool unfoldGEPSelect(GetElementPtrInst &GEPI) {
// Check whether the GEP has exactly one select operand and all indices
// will become constant after the transform.
SelectInst *Sel = dyn_cast<SelectInst>(GEPI.getPointerOperand());
Expand Down Expand Up @@ -4029,67 +4029,104 @@ class AggLoadStoreRewriter : public InstVisitor<AggLoadStoreRewriter, bool> {
return true;
}

// Fold gep (phi ptr1, ptr2) => phi gep(ptr1), gep(ptr2)
bool foldGEPPhi(GetElementPtrInst &GEPI) {
if (!GEPI.hasAllConstantIndices())
return false;
// Unfold gep (phi ptr1, ptr2), idx
// => phi ((gep ptr1, idx), (gep ptr2, idx))
// and gep ptr, (phi idx1, idx2)
// => phi ((gep ptr, idx1), (gep ptr, idx2))
bool unfoldGEPPhi(GetElementPtrInst &GEPI) {
// To prevent infinitely expanding recursive phis, bail if the GEP pointer
// operand (looking through the phi if it is the phi we want to unfold) is
// an instruction besides an alloca.
PHINode *Phi = dyn_cast<PHINode>(GEPI.getPointerOperand());
auto IsInvalidPointerOperand = [](Value *V) {
return isa<Instruction>(V) && !isa<AllocaInst>(V);
};
if (Phi) {
if (any_of(Phi->operands(), IsInvalidPointerOperand))
return false;
} else {
if (IsInvalidPointerOperand(GEPI.getPointerOperand()))
return false;
}
// Check whether the GEP has exactly one phi operand (including the pointer
// operand) and all indices will become constant after the transform.
for (Value *Op : GEPI.indices()) {
if (auto *SI = dyn_cast<PHINode>(Op)) {
if (Phi)
return false;

Phi = SI;
if (!all_of(Phi->incoming_values(),
[](Value *V) { return isa<ConstantInt>(V); }))
return false;
continue;
}

PHINode *PHI = cast<PHINode>(GEPI.getPointerOperand());
if (GEPI.getParent() != PHI->getParent() ||
llvm::any_of(PHI->incoming_values(), [](Value *In) {
Instruction *I = dyn_cast<Instruction>(In);
return !I || isa<GetElementPtrInst>(I) || isa<PHINode>(I) ||
succ_empty(I->getParent()) ||
!I->getParent()->isLegalToHoistInto();
}))
if (!isa<ConstantInt>(Op))
return false;
}

if (!Phi)
return false;

LLVM_DEBUG(dbgs() << " Rewriting gep(phi) -> phi(gep):\n";
dbgs() << " original: " << *PHI << "\n";
dbgs() << " original: " << *Phi << "\n";
dbgs() << " " << GEPI << "\n";);

SmallVector<Value *, 4> Index(GEPI.indices());
auto GetNewOps = [&](Value *PhiOp) {
SmallVector<Value *> NewOps;
for (Value *Op : GEPI.operands())
if (Op == Phi)
NewOps.push_back(PhiOp);
else
NewOps.push_back(Op);
return NewOps;
};

IRB.SetInsertPoint(Phi);
PHINode *NewPhi = IRB.CreatePHI(GEPI.getType(), Phi->getNumIncomingValues(),
Phi->getName() + ".sroa.phi");

bool IsInBounds = GEPI.isInBounds();
IRB.SetInsertPoint(GEPI.getParent(), GEPI.getParent()->getFirstNonPHIIt());
PHINode *NewPN = IRB.CreatePHI(GEPI.getType(), PHI->getNumIncomingValues(),
PHI->getName() + ".sroa.phi");
for (unsigned I = 0, E = PHI->getNumIncomingValues(); I != E; ++I) {
BasicBlock *B = PHI->getIncomingBlock(I);
Value *NewVal = nullptr;
int Idx = NewPN->getBasicBlockIndex(B);
if (Idx >= 0) {
NewVal = NewPN->getIncomingValue(Idx);
Type *SourceTy = GEPI.getSourceElementType();
// We only handle arguments, constants, and static allocas here, so we can
// insert GEPs at the end of the entry block.
IRB.SetInsertPoint(GEPI.getFunction()->getEntryBlock().getTerminator());
for (unsigned I = 0, E = Phi->getNumIncomingValues(); I != E; ++I) {
Value *Op = Phi->getIncomingValue(I);
BasicBlock *BB = Phi->getIncomingBlock(I);
Value *NewGEP;
if (int NI = NewPhi->getBasicBlockIndex(BB); NI >= 0) {
NewGEP = NewPhi->getIncomingValue(NI);
} else {
Instruction *In = cast<Instruction>(PHI->getIncomingValue(I));

IRB.SetInsertPoint(In->getParent(), std::next(In->getIterator()));
Type *Ty = GEPI.getSourceElementType();
NewVal = IRB.CreateGEP(Ty, In, Index, In->getName() + ".sroa.gep",
IsInBounds);
SmallVector<Value *> NewOps = GetNewOps(Op);
NewGEP =
IRB.CreateGEP(SourceTy, NewOps[0], ArrayRef(NewOps).drop_front(),
Phi->getName() + ".sroa.gep", IsInBounds);
}
NewPN->addIncoming(NewVal, B);
NewPhi->addIncoming(NewGEP, BB);
}

Visited.erase(&GEPI);
GEPI.replaceAllUsesWith(NewPN);
GEPI.replaceAllUsesWith(NewPhi);
GEPI.eraseFromParent();
Visited.insert(NewPN);
enqueueUsers(*NewPN);
Visited.insert(NewPhi);
enqueueUsers(*NewPhi);

LLVM_DEBUG(dbgs() << " to: ";
for (Value *In
: NewPN->incoming_values()) dbgs()
: NewPhi->incoming_values()) dbgs()
<< "\n " << *In;
dbgs() << "\n " << *NewPN << '\n');
dbgs() << "\n " << *NewPhi << '\n');

return true;
}

bool visitGetElementPtrInst(GetElementPtrInst &GEPI) {
if (foldGEPSelect(GEPI))
if (unfoldGEPSelect(GEPI))
return true;

if (isa<PHINode>(GEPI.getPointerOperand()) && foldGEPPhi(GEPI))
if (unfoldGEPPhi(GEPI))
return true;

enqueueUsers(GEPI);
Expand Down
20 changes: 10 additions & 10 deletions llvm/test/Transforms/SROA/phi-and-select.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -114,13 +114,13 @@ define i32 @test3(i32 %x) {
; CHECK-LABEL: @test3(
; CHECK-NEXT: entry:
; CHECK-NEXT: switch i32 [[X:%.*]], label [[BB0:%.*]] [
; CHECK-NEXT: i32 1, label [[BB1:%.*]]
; CHECK-NEXT: i32 2, label [[BB2:%.*]]
; CHECK-NEXT: i32 3, label [[BB3:%.*]]
; CHECK-NEXT: i32 4, label [[BB4:%.*]]
; CHECK-NEXT: i32 5, label [[BB5:%.*]]
; CHECK-NEXT: i32 6, label [[BB6:%.*]]
; CHECK-NEXT: i32 7, label [[BB7:%.*]]
; CHECK-NEXT: i32 1, label [[BB1:%.*]]
; CHECK-NEXT: i32 2, label [[BB2:%.*]]
; CHECK-NEXT: i32 3, label [[BB3:%.*]]
; CHECK-NEXT: i32 4, label [[BB4:%.*]]
; CHECK-NEXT: i32 5, label [[BB5:%.*]]
; CHECK-NEXT: i32 6, label [[BB6:%.*]]
; CHECK-NEXT: i32 7, label [[BB7:%.*]]
; CHECK-NEXT: ]
; CHECK: bb0:
; CHECK-NEXT: br label [[EXIT:%.*]]
Expand Down Expand Up @@ -733,6 +733,7 @@ define void @PR20822(i1 %c1, i1 %c2, ptr %ptr) {
; CHECK-LABEL: @PR20822(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[F_SROA_0:%.*]] = alloca i32, align 4
; CHECK-NEXT: [[F1_SROA_GEP:%.*]] = getelementptr inbounds [[STRUCT_S:%.*]], ptr [[PTR:%.*]], i32 0, i32 0
; CHECK-NEXT: br i1 [[C1:%.*]], label [[IF_END:%.*]], label [[FOR_COND:%.*]]
; CHECK: for.cond:
; CHECK-NEXT: br label [[IF_END]]
Expand All @@ -742,9 +743,8 @@ define void @PR20822(i1 %c1, i1 %c2, ptr %ptr) {
; CHECK: if.then2:
; CHECK-NEXT: br label [[IF_THEN5]]
; CHECK: if.then5:
; CHECK-NEXT: [[F1:%.*]] = phi ptr [ [[PTR:%.*]], [[IF_THEN2]] ], [ [[F_SROA_0]], [[IF_END]] ]
; CHECK-NEXT: [[DOTFCA_0_GEP:%.*]] = getelementptr inbounds [[STRUCT_S:%.*]], ptr [[F1]], i32 0, i32 0
; CHECK-NEXT: store i32 0, ptr [[DOTFCA_0_GEP]], align 4
; CHECK-NEXT: [[F1_SROA_PHI:%.*]] = phi ptr [ [[F1_SROA_GEP]], [[IF_THEN2]] ], [ [[F_SROA_0]], [[IF_END]] ]
; CHECK-NEXT: store i32 0, ptr [[F1_SROA_PHI]], align 4
; CHECK-NEXT: ret void
;
entry:
Expand Down
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