[llvm] r245394 - [BasicAA] Revert r221876 because it can produce incorrect aliasing
Quentin Colombet via llvm-commits
llvm-commits at lists.llvm.org
Tue Aug 25 17:39:21 PDT 2015
Hi Mikhail,
Thanks for the test case, I am looking into it.
Cheers,
-Quentin
> On Aug 25, 2015, at 5:18 PM, Mikhail Zolotukhin <mzolotukhin at apple.com> wrote:
>
> Hi Quentin,
>
> I just found that this revert causes some failures - probably because the original patch also contained a fix for some issue. Could you please take a look at this? (if you don't have time, I'll try to do that a bit later). The attached test case shows the problem:
>
> <r245394.ll>
> (reduced from a real test case - after r245394 we erroneously report NoAlias instead of MustAlias in this case.)
>
> Also, since it has gotten to 3.7 already, we might need a fix for this issue there too.
>
> Thanks,
> Michael
>
>
>> On Aug 18, 2015, at 5:07 PM, Quentin Colombet via llvm-commits <llvm-commits at lists.llvm.org> wrote:
>>
>> Author: qcolombet
>> Date: Tue Aug 18 19:07:20 2015
>> New Revision: 245394
>>
>> URL: https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject-3Frev-3D245394-26view-3Drev&d=BQIGaQ&c=eEvniauFctOgLOKGJOplqw&r=ygVmcuuQ1MUhRUoJm-IgPtgjmvM0byfjlHDg99vufEI&m=JPD1d_NPvshcGEeCbKCVLmlnWxyLhuJD4Am1p-lQVLw&s=uN7xVO3PMr7Ex7x-tHgTpdWAdesokk9Fc62u8-7eqt8&e=
>> Log:
>> [BasicAA] Revert r221876 because it can produce incorrect aliasing
>> information: see PR24468.
>>
>> Removed:
>> llvm/trunk/test/Analysis/BasicAA/zext.ll
>> Modified:
>> llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp
>> llvm/trunk/test/Analysis/BasicAA/phi-aa.ll
>>
>> Modified: llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp
>> URL: https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_llvm_trunk_lib_Analysis_BasicAliasAnalysis.cpp-3Frev-3D245394-26r1-3D245393-26r2-3D245394-26view-3Ddiff&d=BQIGaQ&c=eEvniauFctOgLOKGJOplqw&r=ygVmcuuQ1MUhRUoJm-IgPtgjmvM0byfjlHDg99vufEI&m=JPD1d_NPvshcGEeCbKCVLmlnWxyLhuJD4Am1p-lQVLw&s=kwy7CBCC60PY0_h45LQtQxHRIlCgsdD1nak_oWT7xAs&e=
>> ==============================================================================
>> --- llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp (original)
>> +++ llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp Tue Aug 18 19:07:20 2015
>> @@ -190,14 +190,6 @@ static bool isObjectSize(const Value *V,
>> return V;
>> }
>>
>> - if (ConstantInt *Const = dyn_cast<ConstantInt>(V)) {
>> - // if it's a constant, just convert it to an offset
>> - // and remove the variable.
>> - Offset += Const->getValue();
>> - assert(Scale == 0 && "Constant values don't have a scale");
>> - return V;
>> - }
>> -
>> if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(V)) {
>> if (ConstantInt *RHSC = dyn_cast<ConstantInt>(BOp->getOperand(1))) {
>> switch (BOp->getOpcode()) {
>> @@ -246,10 +238,7 @@ static bool isObjectSize(const Value *V,
>> Value *Result = GetLinearExpression(CastOp, Scale, Offset, Extension, DL,
>> Depth + 1, AC, DT);
>> Scale = Scale.zext(OldWidth);
>> -
>> - // We have to sign-extend even if Extension == EK_ZeroExt as we can't
>> - // decompose a sign extension (i.e. zext(x - 1) != zext(x) - zext(-1)).
>> - Offset = Offset.sext(OldWidth);
>> + Offset = Offset.zext(OldWidth);
>>
>> return Result;
>> }
>> @@ -959,42 +948,12 @@ AliasResult BasicAliasAnalysis::aliasGEP
>> }
>> }
>>
>> + // Try to distinguish something like &A[i][1] against &A[42][0].
>> + // Grab the least significant bit set in any of the scales.
>> if (!GEP1VariableIndices.empty()) {
>> uint64_t Modulo = 0;
>> - bool AllPositive = true;
>> - for (unsigned i = 0, e = GEP1VariableIndices.size(); i != e; ++i) {
>> -
>> - // Try to distinguish something like &A[i][1] against &A[42][0].
>> - // Grab the least significant bit set in any of the scales. We
>> - // don't need std::abs here (even if the scale's negative) as we'll
>> - // be ^'ing Modulo with itself later.
>> + for (unsigned i = 0, e = GEP1VariableIndices.size(); i != e; ++i)
>> Modulo |= (uint64_t)GEP1VariableIndices[i].Scale;
>> -
>> - if (AllPositive) {
>> - // If the Value could change between cycles, then any reasoning about
>> - // the Value this cycle may not hold in the next cycle. We'll just
>> - // give up if we can't determine conditions that hold for every cycle:
>> - const Value *V = GEP1VariableIndices[i].V;
>> -
>> - bool SignKnownZero, SignKnownOne;
>> - ComputeSignBit(const_cast<Value *>(V), SignKnownZero, SignKnownOne, *DL,
>> - 0, AC1, nullptr, DT);
>> -
>> - // Zero-extension widens the variable, and so forces the sign
>> - // bit to zero.
>> - bool IsZExt = GEP1VariableIndices[i].Extension == EK_ZeroExt;
>> - SignKnownZero |= IsZExt;
>> - SignKnownOne &= !IsZExt;
>> -
>> - // If the variable begins with a zero then we know it's
>> - // positive, regardless of whether the value is signed or
>> - // unsigned.
>> - int64_t Scale = GEP1VariableIndices[i].Scale;
>> - AllPositive =
>> - (SignKnownZero && Scale >= 0) || (SignKnownOne && Scale < 0);
>> - }
>> - }
>> -
>> Modulo = Modulo ^ (Modulo & (Modulo - 1));
>>
>> // We can compute the difference between the two addresses
>> @@ -1005,12 +964,6 @@ AliasResult BasicAliasAnalysis::aliasGEP
>> V2Size != MemoryLocation::UnknownSize && ModOffset >= V2Size &&
>> V1Size <= Modulo - ModOffset)
>> return NoAlias;
>> -
>> - // If we know all the variables are positive, then GEP1 >= GEP1BasePtr.
>> - // If GEP1BasePtr > V2 (GEP1BaseOffset > 0) then we know the pointers
>> - // don't alias if V2Size can fit in the gap between V2 and GEP1BasePtr.
>> - if (AllPositive && GEP1BaseOffset > 0 && V2Size <= (uint64_t)GEP1BaseOffset)
>> - return NoAlias;
>> }
>>
>> // Statically, we can see that the base objects are the same, but the
>>
>> Modified: llvm/trunk/test/Analysis/BasicAA/phi-aa.ll
>> URL: https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_llvm_trunk_test_Analysis_BasicAA_phi-2Daa.ll-3Frev-3D245394-26r1-3D245393-26r2-3D245394-26view-3Ddiff&d=BQIGaQ&c=eEvniauFctOgLOKGJOplqw&r=ygVmcuuQ1MUhRUoJm-IgPtgjmvM0byfjlHDg99vufEI&m=JPD1d_NPvshcGEeCbKCVLmlnWxyLhuJD4Am1p-lQVLw&s=cehKOdzc-AApufyxhgLw_vGfRZjjrQELvwb9VtQhG6Y&e=
>> ==============================================================================
>> --- llvm/trunk/test/Analysis/BasicAA/phi-aa.ll (original)
>> +++ llvm/trunk/test/Analysis/BasicAA/phi-aa.ll Tue Aug 18 19:07:20 2015
>> @@ -39,7 +39,6 @@ return:
>>
>> ; CHECK-LABEL: pr18068
>> ; CHECK: MayAlias: i32* %0, i32* %arrayidx5
>> -; CHECK: NoAlias: i32* %arrayidx13, i32* %arrayidx5
>>
>> define i32 @pr18068(i32* %jj7, i32* %j) {
>> entry:
>>
>> Removed: llvm/trunk/test/Analysis/BasicAA/zext.ll
>> URL: https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_llvm_trunk_test_Analysis_BasicAA_zext.ll-3Frev-3D245393-26view-3Dauto&d=BQIGaQ&c=eEvniauFctOgLOKGJOplqw&r=ygVmcuuQ1MUhRUoJm-IgPtgjmvM0byfjlHDg99vufEI&m=JPD1d_NPvshcGEeCbKCVLmlnWxyLhuJD4Am1p-lQVLw&s=wdYogyNitYplNTvO10DlNZoWUJYAlarw-Tep_HnkBAc&e=
>> ==============================================================================
>> --- llvm/trunk/test/Analysis/BasicAA/zext.ll (original)
>> +++ llvm/trunk/test/Analysis/BasicAA/zext.ll (removed)
>> @@ -1,209 +0,0 @@
>> -; RUN: opt < %s -basicaa -aa-eval -print-all-alias-modref-info -disable-output 2>&1 | FileCheck %s
>> -target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
>> -target triple = "x86_64-unknown-linux-gnu"
>> -
>> -; CHECK-LABEL: test_with_zext
>> -; CHECK: NoAlias: i8* %a, i8* %b
>> -
>> -define void @test_with_zext() {
>> - %1 = tail call i8* @malloc(i64 120)
>> - %a = getelementptr inbounds i8, i8* %1, i64 8
>> - %2 = getelementptr inbounds i8, i8* %1, i64 16
>> - %3 = zext i32 3 to i64
>> - %b = getelementptr inbounds i8, i8* %2, i64 %3
>> - ret void
>> -}
>> -
>> -; CHECK-LABEL: test_with_lshr
>> -; CHECK: NoAlias: i8* %a, i8* %b
>> -
>> -define void @test_with_lshr(i64 %i) {
>> - %1 = tail call i8* @malloc(i64 120)
>> - %a = getelementptr inbounds i8, i8* %1, i64 8
>> - %2 = getelementptr inbounds i8, i8* %1, i64 16
>> - %3 = lshr i64 %i, 2
>> - %b = getelementptr inbounds i8, i8* %2, i64 %3
>> - ret void
>> -}
>> -
>> -; CHECK-LABEL: test_with_a_loop
>> -; CHECK: NoAlias: i8* %a, i8* %b
>> -
>> -define void @test_with_a_loop(i8* %mem) {
>> - br label %for.loop
>> -
>> -for.loop:
>> - %i = phi i32 [ 0, %0 ], [ %i.plus1, %for.loop ]
>> - %a = getelementptr inbounds i8, i8* %mem, i64 8
>> - %a.plus1 = getelementptr inbounds i8, i8* %mem, i64 16
>> - %i.64 = zext i32 %i to i64
>> - %b = getelementptr inbounds i8, i8* %a.plus1, i64 %i.64
>> - %i.plus1 = add nuw nsw i32 %i, 1
>> - %cmp = icmp eq i32 %i.plus1, 10
>> - br i1 %cmp, label %for.loop.exit, label %for.loop
>> -
>> -for.loop.exit:
>> - ret void
>> -}
>> -
>> -; CHECK-LABEL: test_with_varying_base_pointer_in_loop
>> -; CHECK: NoAlias: i8* %a, i8* %b
>> -
>> -define void @test_with_varying_base_pointer_in_loop(i8* %mem.orig) {
>> - br label %for.loop
>> -
>> -for.loop:
>> - %mem = phi i8* [ %mem.orig, %0 ], [ %mem.plus1, %for.loop ]
>> - %i = phi i32 [ 0, %0 ], [ %i.plus1, %for.loop ]
>> - %a = getelementptr inbounds i8, i8* %mem, i64 8
>> - %a.plus1 = getelementptr inbounds i8, i8* %mem, i64 16
>> - %i.64 = zext i32 %i to i64
>> - %b = getelementptr inbounds i8, i8* %a.plus1, i64 %i.64
>> - %i.plus1 = add nuw nsw i32 %i, 1
>> - %mem.plus1 = getelementptr inbounds i8, i8* %mem, i64 8
>> - %cmp = icmp eq i32 %i.plus1, 10
>> - br i1 %cmp, label %for.loop.exit, label %for.loop
>> -
>> -for.loop.exit:
>> - ret void
>> -}
>> -
>> -; CHECK-LABEL: test_sign_extension
>> -; CHECK: PartialAlias: i64* %b.i64, i8* %a
>> -
>> -define void @test_sign_extension(i32 %p) {
>> - %1 = tail call i8* @malloc(i64 120)
>> - %p.64 = zext i32 %p to i64
>> - %a = getelementptr inbounds i8, i8* %1, i64 %p.64
>> - %p.minus1 = add i32 %p, -1
>> - %p.minus1.64 = zext i32 %p.minus1 to i64
>> - %b.i8 = getelementptr inbounds i8, i8* %1, i64 %p.minus1.64
>> - %b.i64 = bitcast i8* %b.i8 to i64*
>> - ret void
>> -}
>> -
>> -; CHECK-LABEL: test_fe_tools
>> -; CHECK: PartialAlias: i32* %a, i32* %b
>> -
>> -define void @test_fe_tools([8 x i32]* %values) {
>> - br label %reorder
>> -
>> -for.loop:
>> - %i = phi i32 [ 0, %reorder ], [ %i.next, %for.loop ]
>> - %idxprom = zext i32 %i to i64
>> - %b = getelementptr inbounds [8 x i32], [8 x i32]* %values, i64 0, i64 %idxprom
>> - %i.next = add nuw nsw i32 %i, 1
>> - %1 = icmp eq i32 %i.next, 10
>> - br i1 %1, label %for.loop.exit, label %for.loop
>> -
>> -reorder:
>> - %a = getelementptr inbounds [8 x i32], [8 x i32]* %values, i64 0, i64 1
>> - br label %for.loop
>> -
>> -for.loop.exit:
>> - ret void
>> -}
>> -
>> - at b = global i32 0, align 4
>> - at d = global i32 0, align 4
>> -
>> -; CHECK-LABEL: test_spec2006
>> -; CHECK: PartialAlias: i32** %x, i32** %y
>> -
>> -define void @test_spec2006() {
>> - %h = alloca [1 x [2 x i32*]], align 16
>> - %d.val = load i32, i32* @d, align 4
>> - %d.promoted = sext i32 %d.val to i64
>> - %1 = icmp slt i32 %d.val, 2
>> - br i1 %1, label %.lr.ph, label %3
>> -
>> -.lr.ph: ; preds = %0
>> - br label %2
>> -
>> -; <label>:2 ; preds = %.lr.ph, %2
>> - %i = phi i32 [ %d.val, %.lr.ph ], [ %i.plus1, %2 ]
>> - %i.promoted = sext i32 %i to i64
>> - %x = getelementptr inbounds [1 x [2 x i32*]], [1 x [2 x i32*]]* %h, i64 0, i64 %d.promoted, i64 %i.promoted
>> - %i.plus1 = add nsw i32 %i, 1
>> - %cmp = icmp slt i32 %i.plus1, 2
>> - br i1 %cmp, label %2, label %3
>> -
>> -; <label>:3 ; preds = %._crit_edge, %0
>> - %y = getelementptr inbounds [1 x [2 x i32*]], [1 x [2 x i32*]]* %h, i64 0, i64 0, i64 1
>> - ret void
>> -}
>> -
>> -; CHECK-LABEL: test_modulo_analysis_easy_case
>> -; CHECK: NoAlias: i32** %x, i32** %y
>> -
>> -define void @test_modulo_analysis_easy_case(i64 %i) {
>> - %h = alloca [1 x [2 x i32*]], align 16
>> - %x = getelementptr inbounds [1 x [2 x i32*]], [1 x [2 x i32*]]* %h, i64 0, i64 %i, i64 0
>> - %y = getelementptr inbounds [1 x [2 x i32*]], [1 x [2 x i32*]]* %h, i64 0, i64 0, i64 1
>> - ret void
>> -}
>> -
>> -; CHECK-LABEL: test_modulo_analysis_in_loop
>> -; CHECK: NoAlias: i32** %x, i32** %y
>> -
>> -define void @test_modulo_analysis_in_loop() {
>> - %h = alloca [1 x [2 x i32*]], align 16
>> - br label %for.loop
>> -
>> -for.loop:
>> - %i = phi i32 [ 0, %0 ], [ %i.plus1, %for.loop ]
>> - %i.promoted = sext i32 %i to i64
>> - %x = getelementptr inbounds [1 x [2 x i32*]], [1 x [2 x i32*]]* %h, i64 0, i64 %i.promoted, i64 0
>> - %y = getelementptr inbounds [1 x [2 x i32*]], [1 x [2 x i32*]]* %h, i64 0, i64 0, i64 1
>> - %i.plus1 = add nsw i32 %i, 1
>> - %cmp = icmp slt i32 %i.plus1, 2
>> - br i1 %cmp, label %for.loop, label %for.loop.exit
>> -
>> -for.loop.exit:
>> - ret void
>> -}
>> -
>> -; CHECK-LABEL: test_modulo_analysis_with_global
>> -; CHECK: PartialAlias: i32** %x, i32** %y
>> -
>> -define void @test_modulo_analysis_with_global() {
>> - %h = alloca [1 x [2 x i32*]], align 16
>> - %b = load i32, i32* @b, align 4
>> - %b.promoted = sext i32 %b to i64
>> - br label %for.loop
>> -
>> -for.loop:
>> - %i = phi i32 [ 0, %0 ], [ %i.plus1, %for.loop ]
>> - %i.promoted = sext i32 %i to i64
>> - %x = getelementptr inbounds [1 x [2 x i32*]], [1 x [2 x i32*]]* %h, i64 0, i64 %i.promoted, i64 %b.promoted
>> - %y = getelementptr inbounds [1 x [2 x i32*]], [1 x [2 x i32*]]* %h, i64 0, i64 0, i64 1
>> - %i.plus1 = add nsw i32 %i, 1
>> - %cmp = icmp slt i32 %i.plus1, 2
>> - br i1 %cmp, label %for.loop, label %for.loop.exit
>> -
>> -for.loop.exit:
>> - ret void
>> -}
>> -
>> -; CHECK-LABEL: test_const_eval
>> -; CHECK: NoAlias: i8* %a, i8* %b
>> -define void @test_const_eval(i8* %ptr, i64 %offset) {
>> - %a = getelementptr inbounds i8, i8* %ptr, i64 %offset
>> - %a.dup = getelementptr inbounds i8, i8* %ptr, i64 %offset
>> - %three = zext i32 3 to i64
>> - %b = getelementptr inbounds i8, i8* %a.dup, i64 %three
>> - ret void
>> -}
>> -
>> -; CHECK-LABEL: test_const_eval_scaled
>> -; CHECK: MustAlias: i8* %a, i8* %b
>> -define void @test_const_eval_scaled(i8* %ptr) {
>> - %three = zext i32 3 to i64
>> - %six = mul i64 %three, 2
>> - %a = getelementptr inbounds i8, i8* %ptr, i64 %six
>> - %b = getelementptr inbounds i8, i8* %ptr, i64 6
>> - ret void
>> -}
>> -
>> -; Function Attrs: nounwind
>> -declare noalias i8* @malloc(i64)
>>
>>
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