Index: lib/Transforms/Scalar/LoopDataPrefetch.cpp =================================================================== --- lib/Transforms/Scalar/LoopDataPrefetch.cpp +++ lib/Transforms/Scalar/LoopDataPrefetch.cpp @@ -243,6 +243,10 @@ if (ItersAhead > getMaxPrefetchIterationsAhead()) return MadeChange; + unsigned LoopConstantTripCount = SE->getSmallConstantMaxTripCount(L); + if (LoopConstantTripCount && LoopConstantTripCount < ItersAhead) + return MadeChange; + LLVM_DEBUG(dbgs() << "Prefetching " << ItersAhead << " iterations ahead (loop size: " << LoopSize << ") in " << L->getHeader()->getParent()->getName() << ": " << *L); Index: test/CodeGen/SystemZ/prefetch-02.ll =================================================================== --- /dev/null +++ test/CodeGen/SystemZ/prefetch-02.ll @@ -0,0 +1,33 @@ +; RUN: llc < %s -mtriple=s390x-linux-gnu -mcpu=z14 -prefetch-distance=100 \ +; RUN: -stop-after=loop-data-prefetch | FileCheck %s -check-prefix=FAR-PREFETCH +; RUN: llc < %s -mtriple=s390x-linux-gnu -mcpu=z14 -prefetch-distance=50 \ +; RUN: -stop-after=loop-data-prefetch | FileCheck %s -check-prefix=NEAR-PREFETCH +; +; Check that prefetches are not emitted when the known constant trip count of +; the loop is smaller than the estimated "iterations ahead" of the prefetch. +; +; FAR-PREFETCH-LABEL: fun +; FAR-PREFETCH-NOT: call void @llvm.prefetch + +; NEAR-PREFETCH-LABEL: fun +; NEAR-PREFETCH: call void @llvm.prefetch + + +define void @fun(i32* nocapture %Src, i32* nocapture readonly %Dst) { +entry: + br label %for.body + +for.cond.cleanup: ; preds = %for.body + ret void + +for.body: ; preds = %for.body, %entry + %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next.9, %for.body ] + %arrayidx = getelementptr inbounds i32, i32* %Dst, i64 %indvars.iv + %0 = load i32, i32* %arrayidx, align 4 + %arrayidx2 = getelementptr inbounds i32, i32* %Src, i64 %indvars.iv + store i32 %0, i32* %arrayidx2, align 4 + %indvars.iv.next.9 = add nuw nsw i64 %indvars.iv, 1600 + %cmp.9 = icmp ult i64 %indvars.iv.next.9, 11200 + br i1 %cmp.9, label %for.body, label %for.cond.cleanup +} +