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release/19.x: Revert " [LICM] Fold associative binary ops to promote code hoisting (#81608)" #100094

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Jul 24, 2024
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release/19.x: Revert " [LICM] Fold associative binary ops to promote code hoisting (#81608)" #100094

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62 changes: 0 additions & 62 deletions llvm/lib/Transforms/Scalar/LICM.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -113,8 +113,6 @@ STATISTIC(NumFPAssociationsHoisted, "Number of invariant FP expressions "
STATISTIC(NumIntAssociationsHoisted,
"Number of invariant int expressions "
"reassociated and hoisted out of the loop");
STATISTIC(NumBOAssociationsHoisted, "Number of invariant BinaryOp expressions "
"reassociated and hoisted out of the loop");

/// Memory promotion is enabled by default.
static cl::opt<bool>
Expand Down Expand Up @@ -2781,60 +2779,6 @@ static bool hoistMulAddAssociation(Instruction &I, Loop &L,
return true;
}

/// Reassociate general associative binary expressions of the form
///
/// 1. "(LV op C1) op C2" ==> "LV op (C1 op C2)"
///
/// where op is an associative binary op, LV is a loop variant, and C1 and C2
/// are loop invariants that we want to hoist.
///
/// TODO: This can be extended to more cases such as
/// 2. "C1 op (C2 op LV)" ==> "(C1 op C2) op LV"
/// 3. "(C1 op LV) op C2" ==> "LV op (C1 op C2)" if op is commutative
/// 4. "C1 op (LV op C2)" ==> "(C1 op C2) op LV" if op is commutative
static bool hoistBOAssociation(Instruction &I, Loop &L,
ICFLoopSafetyInfo &SafetyInfo,
MemorySSAUpdater &MSSAU, AssumptionCache *AC,
DominatorTree *DT) {
BinaryOperator *BO = dyn_cast<BinaryOperator>(&I);
if (!BO || !BO->isAssociative())
return false;

Instruction::BinaryOps Opcode = BO->getOpcode();
BinaryOperator *Op0 = dyn_cast<BinaryOperator>(BO->getOperand(0));

// Transform: "(LV op C1) op C2" ==> "LV op (C1 op C2)"
if (Op0 && Op0->getOpcode() == Opcode) {
Value *LV = Op0->getOperand(0);
Value *C1 = Op0->getOperand(1);
Value *C2 = BO->getOperand(1);

if (L.isLoopInvariant(LV) || !L.isLoopInvariant(C1) ||
!L.isLoopInvariant(C2))
return false;

auto *Preheader = L.getLoopPreheader();
assert(Preheader && "Loop is not in simplify form?");
IRBuilder<> Builder(Preheader->getTerminator());
Value *Inv = Builder.CreateBinOp(Opcode, C1, C2, "invariant.op");

auto *NewBO =
BinaryOperator::Create(Opcode, LV, Inv, BO->getName() + ".reass", BO);
NewBO->copyIRFlags(BO);
BO->replaceAllUsesWith(NewBO);
eraseInstruction(*BO, SafetyInfo, MSSAU);

// Note: (LV op C1) might not be erased if it has more uses than the one we
// just replaced.
if (Op0->use_empty())
eraseInstruction(*Op0, SafetyInfo, MSSAU);

return true;
}

return false;
}

static bool hoistArithmetics(Instruction &I, Loop &L,
ICFLoopSafetyInfo &SafetyInfo,
MemorySSAUpdater &MSSAU, AssumptionCache *AC,
Expand Down Expand Up @@ -2872,12 +2816,6 @@ static bool hoistArithmetics(Instruction &I, Loop &L,
return true;
}

if (hoistBOAssociation(I, L, SafetyInfo, MSSAU, AC, DT)) {
++NumHoisted;
++NumBOAssociationsHoisted;
return true;
}

return false;
}

Expand Down
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