diff --git a/llvm/lib/Analysis/DependenceAnalysis.cpp b/llvm/lib/Analysis/DependenceAnalysis.cpp --- a/llvm/lib/Analysis/DependenceAnalysis.cpp +++ b/llvm/lib/Analysis/DependenceAnalysis.cpp @@ -119,6 +119,11 @@ "dependence vectors for languages that allow the subscript of one " "dimension to underflow or overflow into another dimension.")); +static cl::opt MIVMaxLevelThreshold( + "da-miv-max-level-threshold", cl::init(7), cl::Hidden, cl::ZeroOrMore, + cl::desc("Maximum depth allowed for the recursive algorithm used to " + "explore MIV direction vectors.")); + //===----------------------------------------------------------------------===// // basics @@ -2602,6 +2607,19 @@ const SmallBitVector &Loops, unsigned &DepthExpanded, const SCEV *Delta) const { + // This algorithm has worst case complexity of O(3^n), where 'n' is the number + // of common loop levels. To avoid excessive compile-time, pessimize all the + // results and immediately return when the number of common levels is beyond + // the given threshold. + if (CommonLevels > MIVMaxLevelThreshold) { + LLVM_DEBUG(dbgs() << "Number of common levels exceeded the threshold. MIV " + "direction exploration is terminated.\n"); + for (unsigned K = 1; K <= CommonLevels; ++K) + if (Loops[K]) + Bound[K].DirSet = Dependence::DVEntry::ALL; + return 1; + } + if (Level > CommonLevels) { // record result LLVM_DEBUG(dbgs() << "\t["); diff --git a/llvm/test/Analysis/DependenceAnalysis/MIVMaxLevelThreshold.ll b/llvm/test/Analysis/DependenceAnalysis/MIVMaxLevelThreshold.ll new file mode 100644 --- /dev/null +++ b/llvm/test/Analysis/DependenceAnalysis/MIVMaxLevelThreshold.ll @@ -0,0 +1,86 @@ +; RUN: opt < %s -aa-pipeline=default -passes='print' -da-miv-max-level-threshold=2 + +;; Check to make sure when MIV tests reach a maximum depth level +;; threshold, the resulting dependence is conservatively correct. + +;; for (int i = 0; i < n; i++) +;; for (int j = 0; j < m; j++) +;; for (int k = 0; k < o; k++) +;; A[i+j+k] = A[i-j+k] + B[i+j+k]; + + +; CHECK: Src: %2 = load float, float* %arrayidx, align 4 --> Dst: %5 = load float, float* %arrayidx12, align 4 +; CHECK-NEXT: da analyze - none! +; CHECK: Src: %2 = load float, float* %arrayidx, align 4 --> Dst: store float %add13, float* %arrayidx17, align 4 +; CHECK-NEXT: da analyze - anti [* * *|<]! +; CHECK: Src: %5 = load float, float* %arrayidx12, align 4 --> Dst: store float %add13, float* %arrayidx17, align 4 +; CHECK-NEXT: da analyze - none! + +define void @foo(float* noalias %A, float* noalias %B, i32 signext %m, i32 signext %n, i32 signext %o) { +entry: + %cmp5 = icmp sgt i32 %n, 0 + br i1 %cmp5, label %for.body.preheader, label %for.end23 + +for.body.preheader: ; preds = %entry + %wide.trip.count21 = zext i32 %n to i64 + br label %for.body + +for.body: ; preds = %for.body.preheader, %for.inc21 + %indvars.iv19 = phi i64 [ 0, %for.body.preheader ], [ %indvars.iv.next20, %for.inc21 ] + %cmp23 = icmp sgt i32 %m, 0 + br i1 %cmp23, label %for.body4.preheader, label %for.inc21 + +for.body4.preheader: ; preds = %for.body + %wide.trip.count17 = zext i32 %m to i64 + br label %for.body4 + +for.body4: ; preds = %for.body4.preheader, %for.inc18 + %indvars.iv12 = phi i64 [ 0, %for.body4.preheader ], [ %indvars.iv.next13, %for.inc18 ] + %cmp61 = icmp sgt i32 %o, 0 + br i1 %cmp61, label %for.body8.preheader, label %for.inc18 + +for.body8.preheader: ; preds = %for.body4 + %wide.trip.count = zext i32 %o to i64 + br label %for.body8 + +for.body8: ; preds = %for.body8.preheader, %for.body8 + %indvars.iv = phi i64 [ 0, %for.body8.preheader ], [ %indvars.iv.next, %for.body8 ] + %0 = sub nsw i64 %indvars.iv19, %indvars.iv12 + %1 = add nsw i64 %0, %indvars.iv + %arrayidx = getelementptr inbounds float, float* %A, i64 %1 + %2 = load float, float* %arrayidx, align 4 + %3 = add nuw nsw i64 %indvars.iv19, %indvars.iv12 + %4 = add nuw nsw i64 %3, %indvars.iv + %arrayidx12 = getelementptr inbounds float, float* %B, i64 %4 + %5 = load float, float* %arrayidx12, align 4 + %add13 = fadd fast float %2, %5 + %6 = add nuw nsw i64 %indvars.iv19, %indvars.iv12 + %7 = add nuw nsw i64 %6, %indvars.iv + %arrayidx17 = getelementptr inbounds float, float* %A, i64 %7 + store float %add13, float* %arrayidx17, align 4 + %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1 + %exitcond = icmp ne i64 %indvars.iv.next, %wide.trip.count + br i1 %exitcond, label %for.body8, label %for.inc18.loopexit + +for.inc18.loopexit: ; preds = %for.body8 + br label %for.inc18 + +for.inc18: ; preds = %for.inc18.loopexit, %for.body4 + %indvars.iv.next13 = add nuw nsw i64 %indvars.iv12, 1 + %exitcond18 = icmp ne i64 %indvars.iv.next13, %wide.trip.count17 + br i1 %exitcond18, label %for.body4, label %for.inc21.loopexit + +for.inc21.loopexit: ; preds = %for.inc18 + br label %for.inc21 + +for.inc21: ; preds = %for.inc21.loopexit, %for.body + %indvars.iv.next20 = add nuw nsw i64 %indvars.iv19, 1 + %exitcond22 = icmp ne i64 %indvars.iv.next20, %wide.trip.count21 + br i1 %exitcond22, label %for.body, label %for.end23.loopexit + +for.end23.loopexit: ; preds = %for.inc21 + br label %for.end23 + +for.end23: ; preds = %for.end23.loopexit, %entry + ret void +}