[SCEV] Use APInt for DividesBy when collecting loop guard info (NFC). #163017
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@llvm/pr-subscribers-llvm-analysis Author: Florian Hahn (fhahn) ChangesFollow-up as suggested in #162617. Just use an APInt for DividesBy, as the existing code already operates on APInt and thus handles the case of DividesBy being 1. Full diff: https://github.com/llvm/llvm-project/pull/163017.diff 1 Files Affected:
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 30bcff7c14923..08b37ed16cdeb 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -15633,47 +15633,32 @@ void ScalarEvolution::LoopGuards::collectFromBlock(
return false;
};
- // Checks whether Expr is a non-negative constant, and Divisor is a positive
- // constant, and returns their APInt in ExprVal and in DivisorVal.
- auto GetNonNegExprAndPosDivisor = [&](const SCEV *Expr, const SCEV *Divisor,
- APInt &ExprVal, APInt &DivisorVal) {
- auto *ConstExpr = dyn_cast<SCEVConstant>(Expr);
- auto *ConstDivisor = dyn_cast<SCEVConstant>(Divisor);
- if (!ConstExpr || !ConstDivisor)
- return false;
- ExprVal = ConstExpr->getAPInt();
- DivisorVal = ConstDivisor->getAPInt();
- return ExprVal.isNonNegative() && !DivisorVal.isNonPositive();
- };
-
// Return a new SCEV that modifies \p Expr to the closest number divides by
// \p Divisor and greater or equal than Expr.
- // For now, only handle constant Expr and Divisor.
+ // For now, only handle constant Expr.
auto GetNextSCEVDividesByDivisor = [&](const SCEV *Expr,
- const SCEV *Divisor) {
- APInt ExprVal;
- APInt DivisorVal;
- if (!GetNonNegExprAndPosDivisor(Expr, Divisor, ExprVal, DivisorVal))
+ const APInt &DivisorVal) {
+ const APInt *ExprVal;
+ if (!match(Expr, m_scev_APInt(ExprVal)) || ExprVal->isNegative())
return Expr;
- APInt Rem = ExprVal.urem(DivisorVal);
- if (!Rem.isZero())
- // return the SCEV: Expr + Divisor - Expr % Divisor
- return SE.getConstant(ExprVal + DivisorVal - Rem);
- return Expr;
+ APInt Rem = ExprVal->urem(DivisorVal);
+ if (Rem.isZero())
+ return Expr;
+ // return the SCEV: Expr + Divisor - Expr % Divisor
+ return SE.getConstant(*ExprVal + DivisorVal - Rem);
};
// Return a new SCEV that modifies \p Expr to the closest number divides by
// \p Divisor and less or equal than Expr.
- // For now, only handle constant Expr and Divisor.
+ // For now, only handle constant Expr.
auto GetPreviousSCEVDividesByDivisor = [&](const SCEV *Expr,
- const SCEV *Divisor) {
- APInt ExprVal;
- APInt DivisorVal;
- if (!GetNonNegExprAndPosDivisor(Expr, Divisor, ExprVal, DivisorVal))
+ const APInt &DivisorVal) {
+ const APInt *ExprVal;
+ if (!match(Expr, m_scev_APInt(ExprVal)) || ExprVal->isNegative())
return Expr;
- APInt Rem = ExprVal.urem(DivisorVal);
+ APInt Rem = ExprVal->urem(DivisorVal);
// return the SCEV: Expr - Expr % Divisor
- return SE.getConstant(ExprVal - Rem);
+ return SE.getConstant(*ExprVal - Rem);
};
// Apply divisibilty by \p Divisor on MinMaxExpr with constant values,
@@ -15682,6 +15667,11 @@ void ScalarEvolution::LoopGuards::collectFromBlock(
std::function<const SCEV *(const SCEV *, const SCEV *)>
ApplyDivisibiltyOnMinMaxExpr = [&](const SCEV *MinMaxExpr,
const SCEV *Divisor) {
+ auto *ConstDivisor = dyn_cast<SCEVConstant>(Divisor);
+ if (!ConstDivisor)
+ return MinMaxExpr;
+ const APInt &DivisorVal = ConstDivisor->getAPInt();
+
const SCEV *MinMaxLHS = nullptr, *MinMaxRHS = nullptr;
SCEVTypes SCTy;
if (!IsMinMaxSCEVWithNonNegativeConstant(MinMaxExpr, SCTy, MinMaxLHS,
@@ -15692,8 +15682,8 @@ void ScalarEvolution::LoopGuards::collectFromBlock(
assert(SE.isKnownNonNegative(MinMaxLHS) &&
"Expected non-negative operand!");
auto *DivisibleExpr =
- IsMin ? GetPreviousSCEVDividesByDivisor(MinMaxLHS, Divisor)
- : GetNextSCEVDividesByDivisor(MinMaxLHS, Divisor);
+ IsMin ? GetPreviousSCEVDividesByDivisor(MinMaxLHS, DivisorVal)
+ : GetNextSCEVDividesByDivisor(MinMaxLHS, DivisorVal);
SmallVector<const SCEV *> Ops = {
ApplyDivisibiltyOnMinMaxExpr(MinMaxRHS, Divisor), DivisibleExpr};
return SE.getMinMaxExpr(SCTy, Ops);
@@ -15750,10 +15740,7 @@ void ScalarEvolution::LoopGuards::collectFromBlock(
};
const SCEV *RewrittenLHS = GetMaybeRewritten(LHS);
- const SCEV *DividesBy = nullptr;
- const APInt &Multiple = SE.getConstantMultiple(RewrittenLHS);
- if (!Multiple.isOne())
- DividesBy = SE.getConstant(Multiple);
+ const APInt &DividesBy = SE.getConstantMultiple(RewrittenLHS);
// Collect rewrites for LHS and its transitive operands based on the
// condition.
@@ -15775,21 +15762,21 @@ void ScalarEvolution::LoopGuards::collectFromBlock(
[[fallthrough]];
case CmpInst::ICMP_SLT: {
RHS = SE.getMinusSCEV(RHS, One);
- RHS = DividesBy ? GetPreviousSCEVDividesByDivisor(RHS, DividesBy) : RHS;
+ RHS = GetPreviousSCEVDividesByDivisor(RHS, DividesBy);
break;
}
case CmpInst::ICMP_UGT:
case CmpInst::ICMP_SGT:
RHS = SE.getAddExpr(RHS, One);
- RHS = DividesBy ? GetNextSCEVDividesByDivisor(RHS, DividesBy) : RHS;
+ RHS = GetNextSCEVDividesByDivisor(RHS, DividesBy);
break;
case CmpInst::ICMP_ULE:
case CmpInst::ICMP_SLE:
- RHS = DividesBy ? GetPreviousSCEVDividesByDivisor(RHS, DividesBy) : RHS;
+ RHS = GetPreviousSCEVDividesByDivisor(RHS, DividesBy);
break;
case CmpInst::ICMP_UGE:
case CmpInst::ICMP_SGE:
- RHS = DividesBy ? GetNextSCEVDividesByDivisor(RHS, DividesBy) : RHS;
+ RHS = GetNextSCEVDividesByDivisor(RHS, DividesBy);
break;
default:
break;
@@ -15843,7 +15830,7 @@ void ScalarEvolution::LoopGuards::collectFromBlock(
case CmpInst::ICMP_NE:
if (match(RHS, m_scev_Zero())) {
const SCEV *OneAlignedUp =
- DividesBy ? GetNextSCEVDividesByDivisor(One, DividesBy) : One;
+ GetNextSCEVDividesByDivisor(One, DividesBy);
To = SE.getUMaxExpr(FromRewritten, OneAlignedUp);
}
break;
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✅ With the latest revision this PR passed the C/C++ code formatter. |
nikic
reviewed
Oct 11, 2025
| const APInt &DivisorVal) { | ||
| const APInt *ExprVal; | ||
| if (!match(Expr, m_scev_APInt(ExprVal)) || | ||
| DivisorVal.isNonPositive()) |
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This drops the ExprVal.isNonNegative() check. Is that intentional? (I haven't checked this carefully, but presumably negative values would need special handling for signed min/max?)
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Yep, added the check back, thanks! Looks like this isn't covered by any existing tests in a way that exposes a mis-compile unfortuantely, and I couldn't find a case via llvm-opt-benchmarks and another corpus.
Follow-up as suggested in llvm#162617. Just use an APInt for DividesBy, as the existing code already operates on APInt and thus handles the case of DividesBy being 1.
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…info (NFC). (#163017) Follow-up as suggested in llvm/llvm-project#162617. Just use an APInt for DividesBy, as the existing code already operates on APInt and thus handles the case of DividesBy being 1. PR: llvm/llvm-project#163017
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/186/builds/13122 Here is the relevant piece of the build log for the reference |
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…llvm#163017) Follow-up as suggested in llvm#162617. Just use an APInt for DividesBy, as the existing code already operates on APInt and thus handles the case of DividesBy being 1. PR: llvm#163017
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Follow-up as suggested in #162617.
Just use an APInt for DividesBy, as the existing code already operates on APInt and thus handles the case of DividesBy being 1.