[LLVMbugs] [Bug 11471] New: alias analysis misled by pointer comparison

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=11471

             Bug #: 11471
           Summary: alias analysis misled by pointer comparison
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: richard-llvm at metafoo.co.uk
                CC: llvmbugs at cs.uiuc.edu, nicholas at mxc.ca
    Classification: Unclassified


Consider the following:

; ModuleID = '<stdin>'
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"

%struct.bar = type { i8, double, double, double }

define void @_Z1fP3bar(%struct.bar* noalias sret %agg.result, %struct.bar* %p)
nounwind uwtable {
entry:
  %ok.i = getelementptr inbounds %struct.bar* %agg.result, i64 0, i32 0
  store i8 1, i8* %ok.i, align 1, !tbaa !0
  %cmp.i = icmp eq %struct.bar* %agg.result, %p
  br i1 %cmp.i, label %if.then.i, label %_ZN3barC2EPS_.exit

if.then.i:                                        ; preds = %entry
  %ok2.i = getelementptr inbounds %struct.bar* %p, i64 0, i32 0
  store i8 0, i8* %ok2.i, align 1, !tbaa !0
  %0 = load i8* %ok.i, align 1, !tbaa !0
  %1 = and i8 %0, 1
  %tobool.i = icmp eq i8 %1, 0
  br i1 %tobool.i, label %if.then4.i, label %_ZN3barC2EPS_.exit

if.then4.i:                                       ; preds = %if.then.i
  store i8 1, i8* %ok.i, align 1, !tbaa !0
  br label %_ZN3barC2EPS_.exit

_ZN3barC2EPS_.exit:                               ; preds = %if.then4.i,
%if.then.i, %entry
  ret void
}

!0 = metadata !{metadata !"bool", metadata !1}
!1 = metadata !{metadata !"omnipotent char", metadata !2}
!2 = metadata !{metadata !"Simple C/C++ TBAA", null}

We do not optimize this any further, apparently because the icmp of %agg.result
and %p is causing us to lose the knowledge that those two pointers don't alias.

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