[Loop Vectorizer] Fixed memory confilict checks.
Fixed a bug in run-time checks for possible memory conflicts inside loop.
The bug is in Low <-> High boundaries calculation. The High boundary should be calculated as "last memory access pointer + element size".
Differential revision: https://reviews.llvm.org/D23176
llvm-svn: 279930
diff --git a/llvm/lib/Analysis/LoopAccessAnalysis.cpp b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
index cb0388d..8c761b4 100644
--- a/llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -149,6 +149,19 @@
return OrigSCEV;
}
+/// Calculate Start and End points of memory access.
+/// Let's assume A is the first access and B is a memory access on N-th loop
+/// iteration. Then B is calculated as:
+/// B = A + Step*N .
+/// Step value may be positive or negative.
+/// N is a calculated back-edge taken count:
+/// N = (TripCount > 0) ? RoundDown(TripCount -1 , VF) : 0
+/// Start and End points are calculated in the following way:
+/// Start = UMIN(A, B) ; End = UMAX(A, B) + SizeOfElt,
+/// where SizeOfElt is the size of single memory access in bytes.
+///
+/// There is no conflict when the intervals are disjoint:
+/// NoConflict = (P2.Start >= P1.End) || (P1.Start >= P2.End)
void RuntimePointerChecking::insert(Loop *Lp, Value *Ptr, bool WritePtr,
unsigned DepSetId, unsigned ASId,
const ValueToValueMap &Strides,
@@ -177,12 +190,17 @@
if (CStep->getValue()->isNegative())
std::swap(ScStart, ScEnd);
} else {
- // Fallback case: the step is not constant, but the we can still
+ // Fallback case: the step is not constant, but we can still
// get the upper and lower bounds of the interval by using min/max
// expressions.
ScStart = SE->getUMinExpr(ScStart, ScEnd);
ScEnd = SE->getUMaxExpr(AR->getStart(), ScEnd);
}
+ // Add the size of the pointed element to ScEnd.
+ unsigned EltSize =
+ Ptr->getType()->getPointerElementType()->getScalarSizeInBits() / 8;
+ const SCEV *EltSizeSCEV = SE->getConstant(ScEnd->getType(), EltSize);
+ ScEnd = SE->getAddExpr(ScEnd, EltSizeSCEV);
}
Pointers.emplace_back(Ptr, ScStart, ScEnd, WritePtr, DepSetId, ASId, Sc);
@@ -1870,9 +1888,17 @@
Value *End0 = ChkBuilder.CreateBitCast(A.End, PtrArithTy1, "bc");
Value *End1 = ChkBuilder.CreateBitCast(B.End, PtrArithTy0, "bc");
- Value *Cmp0 = ChkBuilder.CreateICmpULE(Start0, End1, "bound0");
+ // [A|B].Start points to the first accessed byte under base [A|B].
+ // [A|B].End points to the last accessed byte, plus one.
+ // There is no conflict when the intervals are disjoint:
+ // NoConflict = (B.Start >= A.End) || (A.Start >= B.End)
+ //
+ // bound0 = (B.Start < A.End)
+ // bound1 = (A.Start < B.End)
+ // IsConflict = bound0 & bound1
+ Value *Cmp0 = ChkBuilder.CreateICmpULT(Start0, End1, "bound0");
FirstInst = getFirstInst(FirstInst, Cmp0, Loc);
- Value *Cmp1 = ChkBuilder.CreateICmpULE(Start1, End0, "bound1");
+ Value *Cmp1 = ChkBuilder.CreateICmpULT(Start1, End0, "bound1");
FirstInst = getFirstInst(FirstInst, Cmp1, Loc);
Value *IsConflict = ChkBuilder.CreateAnd(Cmp0, Cmp1, "found.conflict");
FirstInst = getFirstInst(FirstInst, IsConflict, Loc);