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[LV/LoopAccesses] Backward dependences are not safe just because the
accesses are via different types Noticed this while generalizing the code for loop distribution. I confirmed with Arnold that this was indeed a bug and managed to create a testcase. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@230647 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -794,11 +794,10 @@ bool MemoryDepChecker::isDependent(const MemAccessInfo &A, unsigned AIdx,
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assert(Val.isStrictlyPositive() && "Expect a positive value");
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assert(Val.isStrictlyPositive() && "Expect a positive value");
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// Positive distance bigger than max vectorization factor.
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if (ATy != BTy) {
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if (ATy != BTy) {
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DEBUG(dbgs() <<
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DEBUG(dbgs() <<
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"LAA: ReadWrite-Write positive dependency with different types\n");
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"LAA: ReadWrite-Write positive dependency with different types\n");
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return false;
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return true;
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}
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}
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unsigned Distance = (unsigned) Val.getZExtValue();
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unsigned Distance = (unsigned) Val.getZExtValue();
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@ -820,6 +819,7 @@ bool MemoryDepChecker::isDependent(const MemAccessInfo &A, unsigned AIdx,
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return true;
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return true;
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}
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}
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// Positive distance bigger than max vectorization factor.
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MaxSafeDepDistBytes = Distance < MaxSafeDepDistBytes ?
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MaxSafeDepDistBytes = Distance < MaxSafeDepDistBytes ?
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Distance : MaxSafeDepDistBytes;
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Distance : MaxSafeDepDistBytes;
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@ -0,0 +1,50 @@
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; RUN: opt -loop-accesses -analyze < %s | FileCheck %s
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; In this loop just because we access A through different types (int, float)
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; we still have a dependence cycle:
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;
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; for (i = 0; i < n; i++) {
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; A_float = (float *) A;
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; A_float[i + 1] = A[i] * B[i];
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; }
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target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
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target triple = "x86_64-apple-macosx10.10.0"
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; CHECK: Report: unsafe dependent memory operations in loop
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; CHECK-NOT: Memory dependences are safe
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@n = global i32 20, align 4
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@B = common global i32* null, align 8
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@A = common global i32* null, align 8
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define void @f() {
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entry:
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%a = load i32** @A, align 8
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%b = load i32** @B, align 8
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br label %for.body
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for.body: ; preds = %for.body, %entry
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%storemerge3 = phi i64 [ 0, %entry ], [ %add, %for.body ]
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%arrayidxA = getelementptr inbounds i32* %a, i64 %storemerge3
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%loadA = load i32* %arrayidxA, align 2
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%arrayidxB = getelementptr inbounds i32* %b, i64 %storemerge3
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%loadB = load i32* %arrayidxB, align 2
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%mul = mul i32 %loadB, %loadA
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%add = add nuw nsw i64 %storemerge3, 1
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%a_float = bitcast i32* %a to float*
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%arrayidxA_plus_2 = getelementptr inbounds float* %a_float, i64 %add
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%mul_float = sitofp i32 %mul to float
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store float %mul_float, float* %arrayidxA_plus_2, align 2
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%exitcond = icmp eq i64 %add, 20
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br i1 %exitcond, label %for.end, label %for.body
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for.end: ; preds = %for.body
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ret void
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}
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