[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 18:14:45 PDT 2015
Hi Mikhail,
I think I found the problem and it boils down to: we want to reapply this piece of code:
-
- // 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);
I.e., we want to do the sext, not the zext.
The problem is that we zext -1 on i32 and get INT_MAX, which did not translate to -1 on i64.
@Hal, Nick, does this sound like the right thing to fix to you?
Cheers,
-Quentin
> On Aug 25, 2015, at 5:39 PM, Quentin Colombet via llvm-commits <llvm-commits at lists.llvm.org> wrote:
>
> 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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