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Aug 30, 2024
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LICM: extend hoistAddSub to unsigned case #106373

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16bb78c
LICM: extend hoistAddSub to unsigned case
artagnon Aug 28, 2024
72ff7ff
hoist-add-sub: turn two tests into positive tests
artagnon Aug 28, 2024
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57 changes: 38 additions & 19 deletions llvm/lib/Transforms/Scalar/LICM.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2537,14 +2537,19 @@ static bool hoistAdd(ICmpInst::Predicate Pred, Value *VariantLHS,
Value *InvariantRHS, ICmpInst &ICmp, Loop &L,
ICFLoopSafetyInfo &SafetyInfo, MemorySSAUpdater &MSSAU,
AssumptionCache *AC, DominatorTree *DT) {
assert(ICmpInst::isSigned(Pred) && "Not supported yet!");
assert(!L.isLoopInvariant(VariantLHS) && "Precondition.");
assert(L.isLoopInvariant(InvariantRHS) && "Precondition.");

bool IsSigned = ICmpInst::isSigned(Pred);

// Try to represent VariantLHS as sum of invariant and variant operands.
using namespace PatternMatch;
Value *VariantOp, *InvariantOp;
if (!match(VariantLHS, m_NSWAdd(m_Value(VariantOp), m_Value(InvariantOp))))
if (IsSigned &&
!match(VariantLHS, m_NSWAdd(m_Value(VariantOp), m_Value(InvariantOp))))
return false;
if (!IsSigned &&
!match(VariantLHS, m_NUWAdd(m_Value(VariantOp), m_Value(InvariantOp))))
return false;

// LHS itself is a loop-variant, try to represent it in the form:
Expand All @@ -2559,17 +2564,20 @@ static bool hoistAdd(ICmpInst::Predicate Pred, Value *VariantLHS,
// normal linear arithmetics). Overflows make things much more complicated, so
// we want to avoid this.
auto &DL = L.getHeader()->getDataLayout();
bool ProvedNoOverflowAfterReassociate =
computeOverflowForSignedSub(InvariantRHS, InvariantOp,
SimplifyQuery(DL, DT, AC, &ICmp)) ==
llvm::OverflowResult::NeverOverflows;
if (!ProvedNoOverflowAfterReassociate)
SimplifyQuery SQ(DL, DT, AC, &ICmp);
if (IsSigned && computeOverflowForSignedSub(InvariantRHS, InvariantOp, SQ) !=
llvm::OverflowResult::NeverOverflows)
return false;
if (!IsSigned &&
computeOverflowForUnsignedSub(InvariantRHS, InvariantOp, SQ) !=
llvm::OverflowResult::NeverOverflows)
return false;
auto *Preheader = L.getLoopPreheader();
assert(Preheader && "Loop is not in simplify form?");
IRBuilder<> Builder(Preheader->getTerminator());
Value *NewCmpOp = Builder.CreateSub(InvariantRHS, InvariantOp, "invariant.op",
/*HasNUW*/ false, /*HasNSW*/ true);
Value *NewCmpOp =
Builder.CreateSub(InvariantRHS, InvariantOp, "invariant.op",
/*HasNUW*/ !IsSigned, /*HasNSW*/ IsSigned);
ICmp.setPredicate(Pred);
ICmp.setOperand(0, VariantOp);
ICmp.setOperand(1, NewCmpOp);
Expand All @@ -2584,14 +2592,19 @@ static bool hoistSub(ICmpInst::Predicate Pred, Value *VariantLHS,
Value *InvariantRHS, ICmpInst &ICmp, Loop &L,
ICFLoopSafetyInfo &SafetyInfo, MemorySSAUpdater &MSSAU,
AssumptionCache *AC, DominatorTree *DT) {
assert(ICmpInst::isSigned(Pred) && "Not supported yet!");
assert(!L.isLoopInvariant(VariantLHS) && "Precondition.");
assert(L.isLoopInvariant(InvariantRHS) && "Precondition.");

bool IsSigned = ICmpInst::isSigned(Pred);

// Try to represent VariantLHS as sum of invariant and variant operands.
using namespace PatternMatch;
Value *VariantOp, *InvariantOp;
if (!match(VariantLHS, m_NSWSub(m_Value(VariantOp), m_Value(InvariantOp))))
if (IsSigned &&
!match(VariantLHS, m_NSWSub(m_Value(VariantOp), m_Value(InvariantOp))))
return false;
if (!IsSigned &&
!match(VariantLHS, m_NUWSub(m_Value(VariantOp), m_Value(InvariantOp))))
return false;

bool VariantSubtracted = false;
Expand All @@ -2613,26 +2626,36 @@ static bool hoistSub(ICmpInst::Predicate Pred, Value *VariantLHS,
// "C1 - C2" does not overflow.
auto &DL = L.getHeader()->getDataLayout();
SimplifyQuery SQ(DL, DT, AC, &ICmp);
if (VariantSubtracted) {
if (VariantSubtracted && IsSigned) {
// C1 - LV < C2 --> LV > C1 - C2
if (computeOverflowForSignedSub(InvariantOp, InvariantRHS, SQ) !=
llvm::OverflowResult::NeverOverflows)
return false;
} else {
} else if (VariantSubtracted && !IsSigned) {
// C1 - LV < C2 --> LV > C1 - C2
if (computeOverflowForUnsignedSub(InvariantOp, InvariantRHS, SQ) !=
llvm::OverflowResult::NeverOverflows)
return false;
} else if (!VariantSubtracted && IsSigned) {
// LV - C1 < C2 --> LV < C1 + C2
if (computeOverflowForSignedAdd(InvariantOp, InvariantRHS, SQ) !=
llvm::OverflowResult::NeverOverflows)
return false;
} else { // !VariantSubtracted && !IsSigned
// LV - C1 < C2 --> LV < C1 + C2
if (computeOverflowForUnsignedAdd(InvariantOp, InvariantRHS, SQ) !=
llvm::OverflowResult::NeverOverflows)
return false;
}
auto *Preheader = L.getLoopPreheader();
assert(Preheader && "Loop is not in simplify form?");
IRBuilder<> Builder(Preheader->getTerminator());
Value *NewCmpOp =
VariantSubtracted
? Builder.CreateSub(InvariantOp, InvariantRHS, "invariant.op",
/*HasNUW*/ false, /*HasNSW*/ true)
/*HasNUW*/ !IsSigned, /*HasNSW*/ IsSigned)
: Builder.CreateAdd(InvariantOp, InvariantRHS, "invariant.op",
/*HasNUW*/ false, /*HasNSW*/ true);
/*HasNUW*/ !IsSigned, /*HasNSW*/ IsSigned);
ICmp.setPredicate(Pred);
ICmp.setOperand(0, VariantOp);
ICmp.setOperand(1, NewCmpOp);
Expand All @@ -2650,10 +2673,6 @@ static bool hoistAddSub(Instruction &I, Loop &L, ICFLoopSafetyInfo &SafetyInfo,
if (!match(&I, m_ICmp(Pred, m_Value(LHS), m_Value(RHS))))
return false;

// TODO: Support unsigned predicates?
if (!ICmpInst::isSigned(Pred))
return false;

// Put variant operand to LHS position.
if (L.isLoopInvariant(LHS)) {
std::swap(LHS, RHS);
Expand Down
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