Do not allow multiple possibly aliasing ptrs in an expression
Relational comparisons should not involve multiple potentially
aliasing pointers. Similarly this should hold for switch conditions
and the two conditions involved in equality comparisons (separately!).
This is a heuristic based on the C semantics that does only allow such
operations when the base pointers do point into the same object.
Since this makes aliasing likely we will bail out early instead of
producing a probably failing runtime check.
llvm-svn: 288516
diff --git a/polly/include/polly/ScopDetection.h b/polly/include/polly/ScopDetection.h
index ef6c95e..2bca384 100644
--- a/polly/include/polly/ScopDetection.h
+++ b/polly/include/polly/ScopDetection.h
@@ -219,6 +219,16 @@
/// Remove cached results for the children of @p R recursively.
void removeCachedResultsRecursively(const Region &R);
+ /// Check if @p S0 and @p S1 do contain multiple possibly aliasing pointers.
+ ///
+ /// @param S0 A expression to check.
+ /// @param S1 Another expression to check or nullptr.
+ /// @param Scope The loop/scope the expressions are checked in.
+ ///
+ /// @returns True, if multiple possibly aliasing pointers are used in @p S0
+ /// (and @p S1 if given).
+ bool involvesMultiplePtrs(const SCEV *S0, const SCEV *S1, Loop *Scope) const;
+
/// Add the region @p AR as over approximated sub-region in @p Context.
///
/// @param AR The non-affine subregion.
diff --git a/polly/lib/Analysis/ScopDetection.cpp b/polly/lib/Analysis/ScopDetection.cpp
index 438d80a..756cb5d 100644
--- a/polly/lib/Analysis/ScopDetection.cpp
+++ b/polly/lib/Analysis/ScopDetection.cpp
@@ -346,6 +346,40 @@
return true;
}
+bool ScopDetection::involvesMultiplePtrs(const SCEV *S0, const SCEV *S1,
+ Loop *Scope) const {
+ SetVector<Value *> Values;
+ findValues(S0, *SE, Values);
+ if (S1)
+ findValues(S1, *SE, Values);
+
+ SmallPtrSet<Value *, 8> PtrVals;
+ for (auto *V : Values) {
+ if (auto *P2I = dyn_cast<PtrToIntInst>(V))
+ V = P2I->getOperand(0);
+
+ if (!V->getType()->isPointerTy())
+ continue;
+
+ auto *PtrSCEV = SE->getSCEVAtScope(V, Scope);
+ if (isa<SCEVConstant>(PtrSCEV))
+ continue;
+
+ auto *BasePtr = dyn_cast<SCEVUnknown>(SE->getPointerBase(PtrSCEV));
+ if (!BasePtr)
+ return true;
+
+ auto *BasePtrVal = BasePtr->getValue();
+ if (PtrVals.insert(BasePtrVal).second) {
+ for (auto *PtrVal : PtrVals)
+ if (PtrVal != BasePtrVal && !AA->isNoAlias(PtrVal, BasePtrVal))
+ return true;
+ }
+ }
+
+ return false;
+}
+
bool ScopDetection::isAffine(const SCEV *S, Loop *Scope,
DetectionContext &Context) const {
@@ -368,6 +402,10 @@
if (IsLoopBranch && L->isLoopLatch(&BB))
return false;
+ // Check for invalid usage of different pointers in one expression.
+ if (involvesMultiplePtrs(ConditionSCEV, nullptr, L))
+ return false;
+
if (isAffine(ConditionSCEV, L, Context))
return true;
@@ -416,6 +454,15 @@
const SCEV *LHS = SE->getSCEVAtScope(ICmp->getOperand(0), L);
const SCEV *RHS = SE->getSCEVAtScope(ICmp->getOperand(1), L);
+ // Check for invalid usage of different pointers in one expression.
+ if (ICmp->isEquality() && involvesMultiplePtrs(LHS, nullptr, L) &&
+ involvesMultiplePtrs(RHS, nullptr, L))
+ return false;
+
+ // Check for invalid usage of different pointers in a relational comparison.
+ if (ICmp->isRelational() && involvesMultiplePtrs(LHS, RHS, L))
+ return false;
+
if (isAffine(LHS, L, Context) && isAffine(RHS, L, Context))
return true;