[llvm] r221876 - Revert r219432 - "Revert "[BasicAA] Revert "Revert r218714 - Make better use of zext and sign information."""
Hal Finkel via llvm-commits
llvm-commits at lists.llvm.org
Fri Aug 14 18:40:33 PDT 2015
Does http://reviews.llvm.org/D11847 fix this?
-Hal
----- Original Message -----
> From: "Quentin Colombet via llvm-commits" <llvm-commits at lists.llvm.org>
> To: "llvm-commits" <llvm-commits at lists.llvm.org>
> Sent: Friday, August 14, 2015 8:34:46 PM
> Subject: Re: [llvm] r221876 - Revert r219432 - "Revert "[BasicAA] Revert "Revert r218714 - Make better use of zext
> and sign information."""
>
>
> +new llvm list
>
>
>
>
> On Aug 14, 2015, at 6:33 PM, Quentin Colombet < qcolombet at apple.com >
> wrote:
>
>
>
> Hi Hal,
>
> Sorry to come back to this old commit, but I believe it miscompiles
> some code:
> https://llvm.org/bugs/show_bug.cgi?id=24468
>
>
> Could you advice on a proper fix or revert?
>
>
> Thanks,
> -Quentin
>
>
>
>
> On Nov 13, 2014, at 1:16 AM, Hal Finkel < hfinkel at anl.gov > wrote:
>
> Author: hfinkel
> Date: Thu Nov 13 03:16:54 2014
> New Revision: 221876
>
> URL: http://llvm.org/viewvc/llvm-project?rev=221876&view=rev
> Log:
> Revert r219432 - "Revert "[BasicAA] Revert "Revert r218714 - Make
> better use of zext and sign information."""
>
> Let's try this again...
>
> This reverts r219432, plus a bug fix.
>
> Description of the bug in r219432 (by Nick):
>
> The bug was using AllPositive to break out of the loop; if the loop
> break
> condition i != e is changed to i != e && AllPositive then the
> test_modulo_analysis_with_global test I've added will fail as the
> Modulo will
> be calculated incorrectly (as the last loop iteration is skipped, so
> Modulo
> isn't updated with its Scale).
>
> Nick also adds this comment:
>
> ComputeSignBit is safe to use in loops as it takes into account phi
> nodes, and
> the == EK_ZeroEx check is safe in loops as, no matter how the
> variable changes
> between iterations, zero-extensions will always guarantee a zero sign
> bit. The
> isValueEqualInPotentialCycles check is therefore definitely not
> needed as all
> the variable analysis holds no matter how the variables change
> between loop
> iterations.
>
> And this patch also adds another enhancement to GetLinearExpression -
> basically
> to convert ConstantInts to Offsets (see test_const_eval and
> test_const_eval_scaled for the situations this improves).
>
> Original commit message:
>
> This reverts r218944, which reverted r218714, plus a bug fix.
>
> Description of the bug in r218714 (by Nick):
>
> The original patch forgot to check if the Scale in VariableGEPIndex
> flipped the
> sign of the variable. The BasicAA pass iterates over the instructions
> in the
> order they appear in the function, and so
> BasicAliasAnalysis::aliasGEP is
> called with the variable it first comes across as parameter GEP1.
> Adding a
> %reorder label puts the definition of %a after %b so aliasGEP is
> called with %b
> as the first parameter and %a as the second. aliasGEP later
> calculates that %a
> == %b + 1 - %idxprom where %idxprom >= 0 (if %a was passed as the
> first
> parameter it would calculate %b == %a - 1 + %idxprom where %idxprom
> >= 0) -
> ignoring that %idxprom is scaled by -1 here lead the patch to
> incorrectly
> conclude that %a > %b.
>
> Revised patch by Nick White, thanks! Thanks to Lang to isolating the
> bug.
> Slightly modified by me to add an early exit from the loop and avoid
> unnecessary, but expensive, function calls.
>
> Original commit message:
>
> Two related things:
>
> 1. Fixes a bug when calculating the offset in GetLinearExpression.
> The code
> previously used zext to extend the offset, so negative offsets were
> converted
> to large positive ones.
>
> 2. Enhance aliasGEP to deduce that, if the difference between two GEP
> allocations is positive and all the variables that govern the offset
> are also
> positive (i.e. the offset is strictly after the higher base pointer),
> then
> locations that fit in the gap between the two base pointers are
> NoAlias.
>
> Patch by Nick White!
>
> Added:
> 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:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp?rev=221876&r1=221875&r2=221876&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp (original)
> +++ llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp Thu Nov 13
> 03:16:54 2014
> @@ -207,6 +207,14 @@ static Value *GetLinearExpression(Value
> 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()) {
> @@ -254,7 +262,10 @@ static Value *GetLinearExpression(Value
> Value *Result = GetLinearExpression(CastOp, Scale, Offset, Extension,
> DL, Depth+1, AT, DT);
> Scale = Scale.zext(OldWidth);
> - Offset = Offset.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);
>
> return Result;
> }
> @@ -1051,12 +1062,45 @@ BasicAliasAnalysis::aliasGEP(const GEPOp
> }
> }
>
> - // 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;
> - for (unsigned i = 0, e = GEP1VariableIndices.size(); i != e; ++i)
> - Modulo |= (uint64_t)GEP1VariableIndices[i].Scale;
> + 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.
> + 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, AT, 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
> @@ -1066,6 +1110,12 @@ BasicAliasAnalysis::aliasGEP(const GEPOp
> if (V1Size != UnknownSize && V2Size != 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:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/BasicAA/phi-aa.ll?rev=221876&r1=221875&r2=221876&view=diff
> ==============================================================================
> --- llvm/trunk/test/Analysis/BasicAA/phi-aa.ll (original)
> +++ llvm/trunk/test/Analysis/BasicAA/phi-aa.ll Thu Nov 13 03:16:54
> 2014
> @@ -39,6 +39,7 @@ return:
>
> ; CHECK-LABEL: pr18068
> ; CHECK: MayAlias: i32* %0, i32* %arrayidx5
> +; CHECK: NoAlias: i32* %arrayidx13, i32* %arrayidx5
>
> define i32 @pr18068(i32* %jj7, i32* %j) {
> entry:
>
> Added: llvm/trunk/test/Analysis/BasicAA/zext.ll
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/BasicAA/zext.ll?rev=221876&view=auto
> ==============================================================================
> --- llvm/trunk/test/Analysis/BasicAA/zext.ll (added)
> +++ llvm/trunk/test/Analysis/BasicAA/zext.ll Thu Nov 13 03:16:54 2014
> @@ -0,0 +1,209 @@
> +; 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* %1, i64 8
> + %2 = getelementptr inbounds i8* %1, i64 16
> + %3 = zext i32 3 to i64
> + %b = getelementptr inbounds 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* %1, i64 8
> + %2 = getelementptr inbounds i8* %1, i64 16
> + %3 = lshr i64 %i, 2
> + %b = getelementptr inbounds 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* %mem, i64 8
> + %a.plus1 = getelementptr inbounds i8* %mem, i64 16
> + %i.64 = zext i32 %i to i64
> + %b = getelementptr inbounds 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* %mem, i64 8
> + %a.plus1 = getelementptr inbounds i8* %mem, i64 16
> + %i.64 = zext i32 %i to i64
> + %b = getelementptr inbounds i8* %a.plus1, i64 %i.64
> + %i.plus1 = add nuw nsw i32 %i, 1
> + %mem.plus1 = getelementptr inbounds 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* %1, i64 %p.64
> + %p.minus1 = add i32 %p, -1
> + %p.minus1.64 = zext i32 %p.minus1 to i64
> + %b.i8 = getelementptr inbounds 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]* %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]* %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* @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*]]* %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*]]* %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*]]* %h, i64 0, i64 %i,
> i64 0
> + %y = getelementptr inbounds [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*]]* %h, i64 0, i64
> %i.promoted, i64 0
> + %y = getelementptr inbounds [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* @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*]]* %h, i64 0, i64
> %i.promoted, i64 %b.promoted
> + %y = getelementptr inbounds [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* %ptr, i64 %offset
> + %a.dup = getelementptr inbounds i8* %ptr, i64 %offset
> + %three = zext i32 3 to i64
> + %b = getelementptr inbounds 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* %ptr, i64 %six
> + %b = getelementptr inbounds i8* %ptr, i64 6
> + ret void
> +}
> +
> +; Function Attrs: nounwind
> +declare noalias i8* @malloc(i64)
>
>
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--
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory
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