Commit 221dfdbe authored by Tom Stellard's avatar Tom Stellard
Browse files

Merging r199351: 

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r199351 | aschwaighofer | 2014-01-15 23:53:18 -0500 (Wed, 15 Jan 2014) | 5 lines

BasicAA: We need to check both access sizes when comparing a gep and an
underlying object of unknown size.

Fixes PR18460.

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llvm-svn: 206053
parent e2151aa2

llvm/lib/Analysis/BasicAliasAnalysis.cpp

+9 −1
Original line number Diff line number Diff line
@@ -1009,7 +1009,15 @@ BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size, 
        return NoAlias;

      }

    } else {

      if (V1Size != UnknownSize) {

      // We have the situation where:

      // +                +

      // | BaseOffset     |

      // ---------------->|

      // |-->V1Size       |-------> V2Size

      // GEP1             V2

      // We need to know that V2Size is not unknown, otherwise we might have

      // stripped a gep with negative index ('gep <ptr>, -1, ...).

      if (V1Size != UnknownSize && V2Size != UnknownSize) {

        if (-(uint64_t)GEP1BaseOffset < V1Size)

          return PartialAlias;

        return NoAlias;

llvm/test/Analysis/BasicAA/noalias-bugs.ll

0 → 100644
+33 −0
Original line number Diff line number Diff line 
; RUN: opt -S -basicaa -dse < %s | 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"

target triple = "x86_64-unknown-linux-gnu"



; We incorrectly returned noalias in the example below for "ptr.64" and

; "either_ptr.64".

; PR18460



%nested = type { %nested.i64 }

%nested.i64 = type { i64 }



define i64 @testcase(%nested * noalias %p1, %nested * noalias %p2,

                     i32 %a, i32 %b) {

  %ptr = getelementptr inbounds %nested* %p1, i64 -1, i32 0

  %ptr.64 = getelementptr inbounds %nested.i64* %ptr, i64 0, i32 0

  %ptr2= getelementptr inbounds %nested* %p2, i64 0, i32 0

  %cmp = icmp ult i32 %a, %b

  %either_ptr = select i1 %cmp, %nested.i64* %ptr2, %nested.i64* %ptr

  %either_ptr.64 = getelementptr inbounds %nested.i64* %either_ptr, i64 0, i32 0



; Because either_ptr.64 and ptr.64 can alias (we used to return noalias)

; elimination of the first store is not valid.



; CHECK: store i64 2

; CHECK: load

; CHECK; store i64 1



  store i64 2, i64* %ptr.64, align 8

  %r = load i64* %either_ptr.64, align 8

  store i64 1, i64* %ptr.64, align 8

  ret i64 %r

}