Index: include/llvm/Analysis/DependenceAnalysis.h =================================================================== --- include/llvm/Analysis/DependenceAnalysis.h +++ include/llvm/Analysis/DependenceAnalysis.h @@ -563,6 +563,11 @@ /// bounds. bool isKnownLessThan(const SCEV *S, const SCEV *Size) const; + /// isKnownNonNegative - Compare to see if S is known not to be negative + /// Uses the fact that S comes from Ptr, which may be an inbound GEP, + /// Proving there is no wrapping going on. + bool isKnownNonNegative(const SCEV *S, const Value *Ptr) const; + /// collectUpperBound - All subscripts are the same type (on my machine, /// an i64). The loop bound may be a smaller type. collectUpperBound /// find the bound, if available, and zero extends it to the Type T. Index: lib/Analysis/DependenceAnalysis.cpp =================================================================== --- lib/Analysis/DependenceAnalysis.cpp +++ lib/Analysis/DependenceAnalysis.cpp @@ -1027,6 +1027,25 @@ return SE->isKnownNegative(LimitedBound); } +bool DependenceInfo::isKnownNonNegative(const SCEV *S, const Value *Ptr) const { + bool Inbounds = false; + if (auto *SrcGEP = dyn_cast(Ptr)) + Inbounds = SrcGEP->isInBounds(); + if (Inbounds) { + if (const SCEVAddRecExpr *AddRec = dyn_cast(S)) { + if (AddRec->isAffine()) { + // We know S is for Ptr, the operand on a load/store, so doesn't wrap. + // If both parts are NonNegative, the end result will be NonNegative + if (SE->isKnownNonNegative(AddRec->getStart()) && + SE->isKnownNonNegative(AddRec->getOperand(1))) + return true; + } + } + } + + return SE->isKnownNonNegative(S); +} + // All subscripts are all the same type. // Loop bound may be smaller (e.g., a char). // Should zero extend loop bound, since it's always >= 0. @@ -3292,13 +3311,13 @@ // FIXME: It may be better to record these sizes and add them as constraints // to the dependency checks. for (int i = 1; i < size; ++i) { - if (!SE->isKnownNonNegative(SrcSubscripts[i])) + if (!isKnownNonNegative(SrcSubscripts[i], SrcPtr)) return false; if (!isKnownLessThan(SrcSubscripts[i], Sizes[i - 1])) return false; - if (!SE->isKnownNonNegative(DstSubscripts[i])) + if (!isKnownNonNegative(DstSubscripts[i], DstPtr)) return false; if (!isKnownLessThan(DstSubscripts[i], Sizes[i - 1])) Index: test/Analysis/DependenceAnalysis/DADelin.ll =================================================================== --- test/Analysis/DependenceAnalysis/DADelin.ll +++ test/Analysis/DependenceAnalysis/DADelin.ll @@ -553,4 +553,38 @@ for.end12: ; preds = %for.inc10, %entry ret double undef -} \ No newline at end of file +} + + +; CHECK-LABEL: nonnegative +define void @nonnegative(i32* nocapture %A, i32 %N) { +; CHECK: da analyze - none! +; CHECK: da analyze - consistent output [0 0|<]! +; CHECK: da analyze - none! +entry: + %cmp44 = icmp eq i32 %N, 0 + br i1 %cmp44, label %exit, label %for.outer + +for.outer: + %h.045 = phi i32 [ %add19, %for.latch ], [ 0, %entry ] + %mul = mul i32 %h.045, %N + br label %for.inner + +for.inner: + %i.043 = phi i32 [ 0, %for.outer ], [ %add16, %for.inner ] + %add = add i32 %i.043, %mul + %arrayidx = getelementptr inbounds i32, i32* %A, i32 %add + store i32 1, i32* %arrayidx, align 4 + store i32 2, i32* %arrayidx, align 4 + %add16 = add nuw i32 %i.043, 1 + %exitcond46 = icmp eq i32 %add16, %N + br i1 %exitcond46, label %for.latch, label %for.inner + +for.latch: + %add19 = add nuw i32 %h.045, 1 + %exitcond47 = icmp eq i32 %add19, %N + br i1 %exitcond47, label %exit, label %for.outer + +exit: + ret void +}