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Teach basic AA about PHI nodes. If all operands of a phi NoAlias another value than it's safe to declare the PHI NoAlias the value. Ditto for MustAlias.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@84038 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng
2009-10-13 22:02:20 +00:00
parent 09fed25a07
commit 50a5914e12
2 changed files with 155 additions and 12 deletions
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lib/Analysis/BasicAliasAnalysis.cpp
+69 -12
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@@ -27,6 +27,7 @@
#include "llvm/Operator.h"
#include "llvm/Pass.h"
#include "llvm/Target/TargetData.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Support/Compiler.h"
@@ -201,7 +202,10 @@ namespace {
static char ID; // Class identification, replacement for typeinfo
BasicAliasAnalysis() : NoAA(&ID) {}
AliasResult alias(const Value *V1, unsigned V1Size,
const Value *V2, unsigned V2Size);
const Value *V2, unsigned V2Size) {
SmallSet<const Value*, 16> VisitedPHIs;
return aliasCheck(V1, V1Size, V2, V2Size, VisitedPHIs);
}
ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
ModRefResult getModRefInfo(CallSite CS1, CallSite CS2);
@@ -218,7 +222,16 @@ namespace {
// aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP instruction
// against another.
AliasResult aliasGEP(const Value *V1, unsigned V1Size,
const Value *V2, unsigned V2Size);
const Value *V2, unsigned V2Size,
SmallSet<const Value*, 16> &VisitedPHIs);
AliasResult aliasPHI(const Value *V1, unsigned V1Size,
const Value *V2, unsigned V2Size,
SmallSet<const Value*, 16> &VisitedPHIs);
AliasResult aliasCheck(const Value *V1, unsigned V1Size,
const Value *V2, unsigned V2Size,
SmallSet<const Value*, 16> &VisitedPHIs);
// CheckGEPInstructions - Check two GEP instructions with known
// must-aliasing base pointers. This checks to see if the index expressions
@@ -339,7 +352,8 @@ BasicAliasAnalysis::getModRefInfo(CallSite CS1, CallSite CS2) {
//
AliasAnalysis::AliasResult
BasicAliasAnalysis::aliasGEP(const Value *V1, unsigned V1Size,
const Value *V2, unsigned V2Size) {
const Value *V2, unsigned V2Size,
SmallSet<const Value*, 16> &VisitedPHIs) {
// If we have two gep instructions with must-alias'ing base pointers, figure
// out if the indexes to the GEP tell us anything about the derived pointer.
// Note that we also handle chains of getelementptr instructions as well as
@@ -359,8 +373,8 @@ BasicAliasAnalysis::aliasGEP(const Value *V1, unsigned V1Size,
GEP1->getOperand(0)->getType() == GEP2->getOperand(0)->getType() &&
// All operands are the same, ignoring the base.
std::equal(GEP1->op_begin()+1, GEP1->op_end(), GEP2->op_begin()+1))
return alias(GEP1->getOperand(0), V1Size, GEP2->getOperand(0), V2Size);
return aliasCheck(GEP1->getOperand(0), V1Size,
GEP2->getOperand(0), V2Size, VisitedPHIs);
// Drill down into the first non-gep value, to test for must-aliasing of
// the base pointers.
@@ -377,7 +391,8 @@ BasicAliasAnalysis::aliasGEP(const Value *V1, unsigned V1Size,
const Value *BasePtr2 = GEP2->getOperand(0);
// Do the base pointers alias?
AliasResult BaseAlias = alias(BasePtr1, ~0U, BasePtr2, ~0U);
AliasResult BaseAlias = aliasCheck(BasePtr1, ~0U, BasePtr2, ~0U,
VisitedPHIs);
if (BaseAlias == NoAlias) return NoAlias;
if (BaseAlias == MustAlias) {
// If the base pointers alias each other exactly, check to see if we can
@@ -413,7 +428,7 @@ BasicAliasAnalysis::aliasGEP(const Value *V1, unsigned V1Size,
SmallVector<Value*, 16> GEPOperands;
const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
AliasResult R = aliasCheck(BasePtr, V1Size, V2, V2Size, VisitedPHIs);
if (R == MustAlias) {
// If there is at least one non-zero constant index, we know they cannot
// alias.
@@ -462,12 +477,47 @@ BasicAliasAnalysis::aliasGEP(const Value *V1, unsigned V1Size,
return MayAlias;
}
// alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
// as array references.
AliasAnalysis::AliasResult
BasicAliasAnalysis::aliasPHI(const Value *V1, unsigned V1Size,
const Value *V2, unsigned V2Size,
SmallSet<const Value*, 16> &VisitedPHIs) {
// The PHI node has already been visited, avoid recursion any further.
if (!VisitedPHIs.insert(V1))
return MayAlias;
SmallSet<Value*, 4> UniqueSrc;
SmallVector<Value*, 4> V1Srcs;
const PHINode *PN = cast<PHINode>(V1);
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
Value *PV1 = PN->getIncomingValue(i);
if (isa<PHINode>(PV1))
// If any of the source itself is a PHI, return MayAlias conservatively
// to avoid compile time explosion.
return MayAlias;
if (UniqueSrc.insert(PV1))
V1Srcs.push_back(PV1);
}
// If all sources of the PHI node NoAlias or MustAlias V2, then returns
// NoAlias / MustAlias. Otherwise, returns MayAlias.
AliasResult Alias = aliasCheck(V1Srcs[0], V1Size, V2, V2Size, VisitedPHIs);
for (unsigned i = 1, e = V1Srcs.size(); i != e; ++i) {
Value *V = V1Srcs[i];
AliasResult ThisAlias = aliasCheck(V, V1Size, V2, V2Size, VisitedPHIs);
if (ThisAlias != Alias)
return MayAlias;
}
return Alias;
}
// aliasCheck - Provide a bunch of ad-hoc rules to disambiguate in common cases,
// such as array references.
//
AliasAnalysis::AliasResult
BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
const Value *V2, unsigned V2Size) {
BasicAliasAnalysis::aliasCheck(const Value *V1, unsigned V1Size,
const Value *V2, unsigned V2Size,
SmallSet<const Value*, 16> &VisitedPHIs) {
// Strip off any casts if they exist.
V1 = V1->stripPointerCasts();
V2 = V2->stripPointerCasts();
@@ -521,7 +571,14 @@ BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
std::swap(V1Size, V2Size);
}
if (isGEP(V1))
return aliasGEP(V1, V1Size, V2, V2Size);
return aliasGEP(V1, V1Size, V2, V2Size, VisitedPHIs);
if (isa<PHINode>(V2) && !isa<PHINode>(V1)) {
std::swap(V1, V2);
std::swap(V1Size, V2Size);
}
if (isa<PHINode>(V1))
return aliasPHI(V1, V1Size, V2, V2Size, VisitedPHIs);
return MayAlias;
}