[llvm] r245394 - [BasicAA] Revert r221876 because it can produce incorrect aliasing

Quentin Colombet via llvm-commits llvm-commits at lists.llvm.org
Tue Aug 18 17:07:20 PDT 2015


Author: qcolombet
Date: Tue Aug 18 19:07:20 2015
New Revision: 245394

URL: http://llvm.org/viewvc/llvm-project?rev=245394&view=rev
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: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp?rev=245394&r1=245393&r2=245394&view=diff
==============================================================================
--- 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: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/BasicAA/phi-aa.ll?rev=245394&r1=245393&r2=245394&view=diff
==============================================================================
--- 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: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/BasicAA/zext.ll?rev=245393&view=auto
==============================================================================
--- 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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