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[BasicAA] Avoid calling GetUnderlyingObject, when the result of a previous call can be reused.

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Recursive calls to aliasCheck from alias[GEP|Select|PHI] may result in a second call to GetUnderlyingObject for a Value, whose underlying object is already computed. This patch ensures that in this situations, the underlying object is not computed again, and the result of the previous call is resued.

https://reviews.llvm.org/D22305

llvm-svn: 278519
This commit is contained in:
Ehsan Amiri 2016-08-12 16:05:03 +00:00
parent 595cd6dff6
commit 03643a9b1f
2 changed files with 31 additions and 16 deletions
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9
include/llvm/Analysis/BasicAliasAnalysis.h
View File

@ -180,14 +180,17 @@ private:
AliasResult aliasPHI(const PHINode *PN, uint64_t PNSize,
const AAMDNodes &PNAAInfo, const Value *V2,
uint64_t V2Size, const AAMDNodes &V2AAInfo);
uint64_t V2Size, const AAMDNodes &V2AAInfo,
const Value *UnderV2);
AliasResult aliasSelect(const SelectInst *SI, uint64_t SISize,
const AAMDNodes &SIAAInfo, const Value *V2,
uint64_t V2Size, const AAMDNodes &V2AAInfo);
uint64_t V2Size, const AAMDNodes &V2AAInfo,
const Value *UnderV2);
AliasResult aliasCheck(const Value *V1, uint64_t V1Size, AAMDNodes V1AATag,
const Value *V2, uint64_t V2Size, AAMDNodes V2AATag);
const Value *V2, uint64_t V2Size, AAMDNodes V2AATag,
const Value *O1 = nullptr, const Value *O2 = nullptr);
};
/// Analysis pass providing a never-invalidated alias analysis result.

38
lib/Analysis/BasicAliasAnalysis.cpp
View File

@ -1140,7 +1140,8 @@ AliasResult BasicAAResult::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size,
return MayAlias;
AliasResult R = aliasCheck(UnderlyingV1, MemoryLocation::UnknownSize,
AAMDNodes(), V2, V2Size, V2AAInfo);
AAMDNodes(), V2, V2Size, V2AAInfo,
nullptr, UnderlyingV2);
if (R != MustAlias)
// If V2 may alias GEP base pointer, conservatively returns MayAlias.
// If V2 is known not to alias GEP base pointer, then the two values
@ -1277,7 +1278,8 @@ static AliasResult MergeAliasResults(AliasResult A, AliasResult B) {
AliasResult BasicAAResult::aliasSelect(const SelectInst *SI, uint64_t SISize,
const AAMDNodes &SIAAInfo,
const Value *V2, uint64_t V2Size,
const AAMDNodes &V2AAInfo) {
const AAMDNodes &V2AAInfo,
const Value *UnderV2) {
// If the values are Selects with the same condition, we can do a more precise
// check: just check for aliases between the values on corresponding arms.
if (const SelectInst *SI2 = dyn_cast<SelectInst>(V2))
@ -1295,12 +1297,14 @@ AliasResult BasicAAResult::aliasSelect(const SelectInst *SI, uint64_t SISize,
// If both arms of the Select node NoAlias or MustAlias V2, then returns
// NoAlias / MustAlias. Otherwise, returns MayAlias.
AliasResult Alias =
aliasCheck(V2, V2Size, V2AAInfo, SI->getTrueValue(), SISize, SIAAInfo);
aliasCheck(V2, V2Size, V2AAInfo, SI->getTrueValue(),
SISize, SIAAInfo, UnderV2);
if (Alias == MayAlias)
return MayAlias;
AliasResult ThisAlias =
aliasCheck(V2, V2Size, V2AAInfo, SI->getFalseValue(), SISize, SIAAInfo);
aliasCheck(V2, V2Size, V2AAInfo, SI->getFalseValue(), SISize, SIAAInfo,
UnderV2);
return MergeAliasResults(ThisAlias, Alias);
}
@ -1308,8 +1312,8 @@ AliasResult BasicAAResult::aliasSelect(const SelectInst *SI, uint64_t SISize,
/// another.
AliasResult BasicAAResult::aliasPHI(const PHINode *PN, uint64_t PNSize,
const AAMDNodes &PNAAInfo, const Value *V2,
uint64_t V2Size,
const AAMDNodes &V2AAInfo) {
uint64_t V2Size, const AAMDNodes &V2AAInfo,
const Value *UnderV2) {
// Track phi nodes we have visited. We use this information when we determine
// value equivalence.
VisitedPhiBBs.insert(PN->getParent());
@ -1388,7 +1392,8 @@ AliasResult BasicAAResult::aliasPHI(const PHINode *PN, uint64_t PNSize,
PNSize = MemoryLocation::UnknownSize;
AliasResult Alias =
aliasCheck(V2, V2Size, V2AAInfo, V1Srcs[0], PNSize, PNAAInfo);
aliasCheck(V2, V2Size, V2AAInfo, V1Srcs[0],
PNSize, PNAAInfo, UnderV2);
// Early exit if the check of the first PHI source against V2 is MayAlias.
// Other results are not possible.
@ -1401,7 +1406,7 @@ AliasResult BasicAAResult::aliasPHI(const PHINode *PN, uint64_t PNSize,
Value *V = V1Srcs[i];
AliasResult ThisAlias =
aliasCheck(V2, V2Size, V2AAInfo, V, PNSize, PNAAInfo);
aliasCheck(V2, V2Size, V2AAInfo, V, PNSize, PNAAInfo, UnderV2);
Alias = MergeAliasResults(ThisAlias, Alias);
if (Alias == MayAlias)
break;
@ -1414,7 +1419,8 @@ AliasResult BasicAAResult::aliasPHI(const PHINode *PN, uint64_t PNSize,
/// array references.
AliasResult BasicAAResult::aliasCheck(const Value *V1, uint64_t V1Size,
AAMDNodes V1AAInfo, const Value *V2,
uint64_t V2Size, AAMDNodes V2AAInfo) {
uint64_t V2Size, AAMDNodes V2AAInfo,
const Value *O1, const Value *O2) {
// If either of the memory references is empty, it doesn't matter what the
// pointer values are.
if (V1Size == 0 || V2Size == 0)
@ -1442,8 +1448,11 @@ AliasResult BasicAAResult::aliasCheck(const Value *V1, uint64_t V1Size,
return NoAlias; // Scalars cannot alias each other
// Figure out what objects these things are pointing to if we can.
const Value *O1 = GetUnderlyingObject(V1, DL, MaxLookupSearchDepth);
const Value *O2 = GetUnderlyingObject(V2, DL, MaxLookupSearchDepth);
if (O1 == nullptr)
O1 = GetUnderlyingObject(V1, DL, MaxLookupSearchDepth);
if (O2 == nullptr)
O2 = GetUnderlyingObject(V2, DL, MaxLookupSearchDepth);
// Null values in the default address space don't point to any object, so they
// don't alias any other pointer.
@ -1526,23 +1535,26 @@ AliasResult BasicAAResult::aliasCheck(const Value *V1, uint64_t V1Size,
if (isa<PHINode>(V2) && !isa<PHINode>(V1)) {
std::swap(V1, V2);
std::swap(O1, O2);
std::swap(V1Size, V2Size);
std::swap(V1AAInfo, V2AAInfo);
}
if (const PHINode *PN = dyn_cast<PHINode>(V1)) {
AliasResult Result = aliasPHI(PN, V1Size, V1AAInfo, V2, V2Size, V2AAInfo);
AliasResult Result = aliasPHI(PN, V1Size, V1AAInfo,
V2, V2Size, V2AAInfo, O2);
if (Result != MayAlias)
return AliasCache[Locs] = Result;
}
if (isa<SelectInst>(V2) && !isa<SelectInst>(V1)) {
std::swap(V1, V2);
std::swap(O1, O2);
std::swap(V1Size, V2Size);
std::swap(V1AAInfo, V2AAInfo);
}
if (const SelectInst *S1 = dyn_cast<SelectInst>(V1)) {
AliasResult Result =
aliasSelect(S1, V1Size, V1AAInfo, V2, V2Size, V2AAInfo);
aliasSelect(S1, V1Size, V1AAInfo, V2, V2Size, V2AAInfo, O2);
if (Result != MayAlias)
return AliasCache[Locs] = Result;
}