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[StackSafety] Bailout more aggressively 

Many edge cases, e.g. wrapped ranges, can be processed
precisely without bailout. However it's very unlikely that
memory access with min/max integer offsets will be
classified as safe anyway.
Early bailout may help with ThinLTO where we can
drop unsafe parameters from summaries.
This commit is contained in:
Vitaly Buka 2020-05-27 13:22:16 -07:00
parent b277382311
commit 14f3357586
1 changed files with 27 additions and 11 deletions
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38
llvm/lib/Analysis/StackSafetyAnalysis.cpp
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@ -85,7 +85,11 @@ struct UseInfo {
explicit UseInfo(unsigned PointerSize) : Range{PointerSize, false} {} explicit UseInfo(unsigned PointerSize) : Range{PointerSize, false} {}
void updateRange(ConstantRange R) { Range = Range.unionWith(R); } void updateRange(const ConstantRange &R) {
assert(!R.isUpperSignWrapped());
Range = Range.unionWith(R);
assert(!Range.isUpperSignWrapped());
}
}; };
raw_ostream &operator<<(raw_ostream &OS, const UseInfo &U) { raw_ostream &operator<<(raw_ostream &OS, const UseInfo &U) {
@ -189,6 +193,11 @@ StackSafetyInfo makeSSI(FunctionInfo Info) {
namespace { namespace {
// Check if we should bailout for such ranges.
bool isUnsafe(const ConstantRange &R) {
return R.isEmptySet() || R.isFullSet() || R.isUpperSignWrapped();
}
class StackSafetyLocalAnalysis { class StackSafetyLocalAnalysis {
Function &F; Function &F;
const DataLayout &DL; const DataLayout &DL;
@ -227,7 +236,7 @@ ConstantRange StackSafetyLocalAnalysis::offsetFrom(Value *Addr, Value *Base) {
AllocaOffsetRewriter Rewriter(SE, Base); AllocaOffsetRewriter Rewriter(SE, Base);
const SCEV *Expr = Rewriter.visit(SE.getSCEV(Addr)); const SCEV *Expr = Rewriter.visit(SE.getSCEV(Addr));
ConstantRange Offset = SE.getSignedRange(Expr); ConstantRange Offset = SE.getSignedRange(Expr);
if (Offset.isEmptySet() || Offset.isFullSet() || Offset.isSignWrappedSet()) if (isUnsafe(Offset))
return UnknownRange; return UnknownRange;
return Offset.sextOrTrunc(PointerSize); return Offset.sextOrTrunc(PointerSize);
} }
@ -238,18 +247,26 @@ StackSafetyLocalAnalysis::getAccessRange(Value *Addr, Value *Base,
// Zero-size loads and stores do not access memory. // Zero-size loads and stores do not access memory.
if (SizeRange.isEmptySet()) if (SizeRange.isEmptySet())
return ConstantRange::getEmpty(PointerSize); return ConstantRange::getEmpty(PointerSize);
assert(!isUnsafe(SizeRange));
ConstantRange AccessStartRange = offsetFrom(Addr, Base); ConstantRange AccessRange = offsetFrom(Addr, Base);
ConstantRange AccessRange = AccessStartRange.add(SizeRange); if (isUnsafe(AccessRange))
assert(!AccessRange.isEmptySet()); return UnknownRange;
if (AccessRange.signedAddMayOverflow(SizeRange) !=
ConstantRange::OverflowResult::NeverOverflows)
return UnknownRange;
AccessRange = AccessRange.add(SizeRange);
if (isUnsafe(AccessRange))
return UnknownRange;
return AccessRange; return AccessRange;
} }
ConstantRange StackSafetyLocalAnalysis::getAccessRange(Value *Addr, Value *Base, ConstantRange StackSafetyLocalAnalysis::getAccessRange(Value *Addr, Value *Base,
TypeSize Size) { TypeSize Size) {
ConstantRange SizeRange = if (Size.isScalable())
Size.isScalable() ? UnknownRange : getRange(0, Size.getFixedSize()); return UnknownRange;
return getAccessRange(Addr, Base, SizeRange); return getAccessRange(Addr, Base, getRange(0, Size.getFixedSize()));
} }
ConstantRange StackSafetyLocalAnalysis::getMemIntrinsicAccessRange( ConstantRange StackSafetyLocalAnalysis::getMemIntrinsicAccessRange(
@ -268,9 +285,8 @@ ConstantRange StackSafetyLocalAnalysis::getMemIntrinsicAccessRange(
const SCEV *Expr = const SCEV *Expr =
SE.getTruncateOrZeroExtend(SE.getSCEV(MI->getLength()), CalculationTy); SE.getTruncateOrZeroExtend(SE.getSCEV(MI->getLength()), CalculationTy);
ConstantRange LenRange = SE.getSignedRange(Expr); ConstantRange LenRange = SE.getSignedRange(Expr);
assert(!LenRange.isEmptySet()); assert(!isUnsafe(LenRange));
if (LenRange.isSignWrappedSet() || LenRange.isFullSet() || if (LenRange.getUpper().isNegative())
LenRange.getUpper().isNegative())
return UnknownRange; return UnknownRange;
LenRange = LenRange.sextOrTrunc(PointerSize); LenRange = LenRange.sextOrTrunc(PointerSize);
ConstantRange SizeRange(APInt::getNullValue(PointerSize), ConstantRange SizeRange(APInt::getNullValue(PointerSize),