Optimistically analyse Phi cycles
Analyse Phis under the starting assumption that they are NoAlias. Recursively
look at their inputs.
If they MayAlias/MustAlias there must be an input that makes them so.
Addresses bug 14351.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@169788 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp
index 279ff06..b0578b9 100644
--- a/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/lib/Analysis/BasicAliasAnalysis.cpp
@@ -1064,48 +1064,20 @@
Location(V2, V2Size, V2TBAAInfo));
if (PN > V2)
std::swap(Locs.first, Locs.second);
-
- // Find the first incoming phi value not from its parent.
- unsigned f = 0;
- while (PN->getIncomingBlock(f) == PN->getParent() &&
- f < PN->getNumIncomingValues()-1)
- ++f;
-
- AliasResult Alias =
- aliasCheck(PN->getIncomingValue(f), PNSize, PNTBAAInfo,
- PN2->getIncomingValueForBlock(PN->getIncomingBlock(f)),
- V2Size, V2TBAAInfo);
- if (Alias == MayAlias)
- return MayAlias;
-
- // If the first source of the PHI nodes NoAlias and the other inputs are
- // the PHI node itself through some amount of recursion this does not add
- // any new information so just return NoAlias.
- // bb:
- // ptr = ptr2 + 1
- // loop:
- // ptr_phi = phi [bb, ptr], [loop, ptr_plus_one]
- // ptr2_phi = phi [bb, ptr2], [loop, ptr2_plus_one]
- // ...
- // ptr_plus_one = gep ptr_phi, 1
- // ptr2_plus_one = gep ptr2_phi, 1
- // We assume for the recursion that the the phis (ptr_phi, ptr2_phi) do
- // not alias each other.
- bool ArePhisAssumedNoAlias = false;
- AliasResult OrigAliasResult = NoAlias;
- if (Alias == NoAlias) {
- // Pretend the phis do not alias.
- assert(AliasCache.count(Locs) &&
- "There must exist an entry for the phi node");
- OrigAliasResult = AliasCache[Locs];
- AliasCache[Locs] = NoAlias;
- ArePhisAssumedNoAlias = true;
- }
+ // Analyse the PHIs' inputs under the assumption that the PHIs are
+ // NoAlias.
+ // If the PHIs are May/MustAlias there must be (recursively) an input
+ // operand from outside the PHIs' cycle that is MayAlias/MustAlias or
+ // there must be an operation on the PHIs within the PHIs' value cycle
+ // that causes a MayAlias.
+ // Pretend the phis do not alias.
+ AliasResult Alias = NoAlias;
+ assert(AliasCache.count(Locs) &&
+ "There must exist an entry for the phi node");
+ AliasResult OrigAliasResult = AliasCache[Locs];
+ AliasCache[Locs] = NoAlias;
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
- if (i == f)
- continue;
-
AliasResult ThisAlias =
aliasCheck(PN->getIncomingValue(i), PNSize, PNTBAAInfo,
PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)),
@@ -1116,7 +1088,7 @@
}
// Reset if speculation failed.
- if (ArePhisAssumedNoAlias && Alias != NoAlias)
+ if (Alias != NoAlias)
AliasCache[Locs] = OrigAliasResult;
return Alias;