[polly] r288516 - Do not allow multiple possibly aliasing ptrs in an expression
Johannes Doerfert via llvm-commits
llvm-commits at lists.llvm.org
Fri Dec 2 09:49:52 PST 2016
Author: jdoerfert
Date: Fri Dec 2 11:49:52 2016
New Revision: 288516
URL: http://llvm.org/viewvc/llvm-project?rev=288516&view=rev
Log:
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.
Modified:
polly/trunk/include/polly/ScopDetection.h
polly/trunk/lib/Analysis/ScopDetection.cpp
Modified: polly/trunk/include/polly/ScopDetection.h
URL: http://llvm.org/viewvc/llvm-project/polly/trunk/include/polly/ScopDetection.h?rev=288516&r1=288515&r2=288516&view=diff
==============================================================================
--- polly/trunk/include/polly/ScopDetection.h (original)
+++ polly/trunk/include/polly/ScopDetection.h Fri Dec 2 11:49:52 2016
@@ -219,6 +219,16 @@ private:
/// 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.
Modified: polly/trunk/lib/Analysis/ScopDetection.cpp
URL: http://llvm.org/viewvc/llvm-project/polly/trunk/lib/Analysis/ScopDetection.cpp?rev=288516&r1=288515&r2=288516&view=diff
==============================================================================
--- polly/trunk/lib/Analysis/ScopDetection.cpp (original)
+++ polly/trunk/lib/Analysis/ScopDetection.cpp Fri Dec 2 11:49:52 2016
@@ -346,6 +346,40 @@ bool ScopDetection::onlyValidRequiredInv
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 @@ bool ScopDetection::isValidSwitch(BasicB
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 @@ bool ScopDetection::isValidBranch(BasicB
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;
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