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llvm-project/llvm/test/Analysis/BasicAA/bug.23540.ll

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[BasicAA] Fix the handling of sext and zext in the analysis of GEPs. Hopefully this will end the GEPs saga! This commit reverts r245394, i.e., it reapplies r221876 while incorporating the fixes from D11847. r221876 was not reapplied alone because it was not safe and D11847 was not applied alone because it needs r221876 to produce correct results. This should fix PR24596. Original commit message for r221876: 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! Message from D11847: Un-revert of r241981 and fix for PR23626. The 'Or' case of GetLinearExpression delegates to 'Add' if possible, and if not it returns an Opaque value. Unfortunately the Scale and Offsets weren't being set (and so defaulted to 0) - and a scale of zero effectively removes the variable from the GEP instruction. This meant that BasicAA would return MustAliases when it should have been returning PartialAliases (and PR23626 was an example of the GVN pass using an incorrect MustAlias to merge loads from what should have been different pointers). Differential Revision: http://reviews.llvm.org/D11847 Patch by Nick White <n.j.white@gmail.com>! llvm-svn: 246502
2015-09-01 06:32:47 +08:00
; RUN: opt < %s -basicaa -aa-eval -print-all-alias-modref-info -disable-output 2>&1 | FileCheck %s
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
@c = external global i32
; CHECK-LABEL: f
[BasicAA] Use MayAlias instead of PartialAlias for fallback. Using various methods, BasicAA tries to determine whether two GetElementPtr memory locations alias when its base pointers are known to be equal. When none of its heuristics are applicable, it falls back to PartialAlias to, according to a comment, protect TBAA making a wrong decision in case of unions and malloc. PartialAlias is not correct, because a PartialAlias result implies that some, but not all, bytes overlap which is not necessarily the case here. AAResults returns the first analysis result that is not MayAlias. BasicAA is always the first alias analysis. When it returns PartialAlias, no other analysis is queried to give a more exact result (which was the intention of returning PartialAlias instead of MayAlias). For instance, ScopedAA could return a more accurate result. The PartialAlias hack was introduced in r131781 (and re-applied in r132632 after some reverts) to fix llvm.org/PR9971 where TBAA returns a wrong NoAlias result due to a union. A test case for the malloc case mentioned in the comment was not provided and I don't think it is affected since it returns an omnipotent char anyway. Since r303851 (https://reviews.llvm.org/D33328) clang does emit specific TBAA for unions anymore (but "omnipotent char" instead). Hence, the PartialAlias workaround is not required anymore. This patch passes the test-suite and check-llvm/check-clang of a self-hoisted build on x64. Reviewed By: hfinkel Differential Revision: https://reviews.llvm.org/D34318 llvm-svn: 305938
2017-06-22 02:25:37 +08:00
; CHECK: MayAlias: i32* %arrayidx, i32* %arrayidx6
[BasicAA] Fix the handling of sext and zext in the analysis of GEPs. Hopefully this will end the GEPs saga! This commit reverts r245394, i.e., it reapplies r221876 while incorporating the fixes from D11847. r221876 was not reapplied alone because it was not safe and D11847 was not applied alone because it needs r221876 to produce correct results. This should fix PR24596. Original commit message for r221876: 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! Message from D11847: Un-revert of r241981 and fix for PR23626. The 'Or' case of GetLinearExpression delegates to 'Add' if possible, and if not it returns an Opaque value. Unfortunately the Scale and Offsets weren't being set (and so defaulted to 0) - and a scale of zero effectively removes the variable from the GEP instruction. This meant that BasicAA would return MustAliases when it should have been returning PartialAliases (and PR23626 was an example of the GVN pass using an incorrect MustAlias to merge loads from what should have been different pointers). Differential Revision: http://reviews.llvm.org/D11847 Patch by Nick White <n.j.white@gmail.com>! llvm-svn: 246502
2015-09-01 06:32:47 +08:00
define void @f() {
%idxprom = zext i32 undef to i64
%add4 = add i32 0, 1
%idxprom5 = zext i32 %add4 to i64
%arrayidx6 = getelementptr inbounds i32, i32* @c, i64 %idxprom5
%arrayidx = getelementptr inbounds i32, i32* @c, i64 %idxprom
ret void
}