[LLVMbugs] [Bug 20303] New: dead store elimination nukes live stores due to later memset

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=20303

            Bug ID: 20303
           Summary: dead store elimination nukes live stores due to later
                    memset
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: nlewycky at google.com
                CC: hfinkel at anl.gov, llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Testcase with opt -basicaa -dse:

; ModuleID = 'z4.ll'
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"

%class.basic_string = type { %"class.__gnu_cxx::__versa_string" }
%"class.__gnu_cxx::__versa_string" = type {
%"class.__gnu_cxx::__sso_string_base" }
%"class.__gnu_cxx::__sso_string_base" = type {
%"struct.__gnu_cxx::__vstring_utility<char, std::char_traits<char>,
std::allocator<char> >::_Alloc_hider", i64, %union.anon }
%"struct.__gnu_cxx::__vstring_utility<char, std::char_traits<char>,
std::allocator<char> >::_Alloc_hider" = type { i8* }
%union.anon = type { i64, [8 x i8] }

; Function Attrs: nounwind
declare void @llvm.memset.p0i8.i64(i8* nocapture, i8, i64, i32, i1) #0

; Function Attrs: noinline nounwind readonly uwtable
declare zeroext i1 @callee_takes_string(%class.basic_string* nonnull) #1 align
2

; Function Attrs: nounwind uwtable
define weak_odr zeroext i1 @test() #2 align 2 {
bb:
  %tmp = alloca %class.basic_string, align 8
  %tmp1 = alloca %class.basic_string, align 8
  %tmp3 = getelementptr inbounds %class.basic_string* %tmp, i64 0, i32 0, i32
0, i32 2
  %tmp4 = bitcast %union.anon* %tmp3 to i8*
  %tmp5 = getelementptr inbounds %class.basic_string* %tmp, i64 0, i32 0, i32
0, i32 0, i32 0
  %tmp6 = getelementptr inbounds %class.basic_string* %tmp, i64 0, i32 0, i32
0, i32 1
  %tmp7 = getelementptr inbounds i8* %tmp4, i64 1
  %tmp8 = bitcast %class.basic_string* %tmp to i8*
  %tmp9 = bitcast i64 0 to i64
  %tmp10 = getelementptr inbounds %class.basic_string* %tmp1, i64 0, i32 0, i32
0, i32 2
  %tmp11 = bitcast %union.anon* %tmp10 to i8*
  %tmp12 = getelementptr inbounds %class.basic_string* %tmp1, i64 0, i32 0, i32
0, i32 0, i32 0
  %tmp13 = getelementptr inbounds %class.basic_string* %tmp1, i64 0, i32 0, i32
0, i32 1
  %tmp14 = getelementptr inbounds i8* %tmp11, i64 1
  %tmp15 = bitcast %class.basic_string* %tmp1 to i8*
  br label %_ZN12basic_stringIcSt11char_traitsIcESaIcEEC2EPKcRKS2_.exit

_ZN12basic_stringIcSt11char_traitsIcESaIcEEC2EPKcRKS2_.exit: ; preds = %bb
  store i8* %tmp4, i8** %tmp5, align 8
  store i8 62, i8* %tmp4, align 8
  store i64 1, i64* %tmp6, align 8
  store i8 0, i8* %tmp7, align 1
  %tmp16 = call zeroext i1 @callee_takes_string(%class.basic_string* nonnull
%tmp)
  br label
%_ZN9__gnu_cxx17__sso_string_baseIcSt11char_traitsIcESaIcEED2Ev.exit3

_ZN9__gnu_cxx17__sso_string_baseIcSt11char_traitsIcESaIcEED2Ev.exit3: ; preds =
%_ZN12basic_stringIcSt11char_traitsIcESaIcEEC2EPKcRKS2_.exit
;; The following stores are eliminated, but they can be read through the call
%tmp17!
  store i8* %tmp11, i8** %tmp12, align 8
  store i8 125, i8* %tmp11, align 8
  store i64 1, i64* %tmp13, align 8
  store i8 0, i8* %tmp14, align 1
  %tmp17 = call zeroext i1 @callee_takes_string(%class.basic_string* nonnull
%tmp1)
;; Commenting out the following memsets brings the stores back.
  call void @llvm.memset.p0i8.i64(i8* %tmp11, i8 -51, i64 16, i32 8, i1 false)
#0
  call void @llvm.memset.p0i8.i64(i8* %tmp15, i8 -51, i64 32, i32 8, i1 false)
#0
  call void @llvm.memset.p0i8.i64(i8* %tmp4, i8 -51, i64 16, i32 8, i1 false)
#0
  call void @llvm.memset.p0i8.i64(i8* %tmp8, i8 -51, i64 32, i32 8, i1 false)
#0
  ret i1 %tmp17
}

attributes #0 = { nounwind }
attributes #1 = { noinline nounwind readonly uwtable
"less-precise-fpmad"="false" "no-frame-pointer-elim"="false"
"no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false"
"no-nans-fp-math"="false" "stack-protector-buffer-size"="8"
"unsafe-fp-math"="false" "use-soft-float"="false" }
attributes #2 = { nounwind uwtable "less-precise-fpmad"="false"
"no-frame-pointer-elim"="false" "no-frame-pointer-elim-non-leaf"
"no-infs-fp-math"="false" "no-nans-fp-math"="false"
"stack-protector-buffer-size"="8" "unsafe-fp-math"="false"
"use-soft-float"="false" }

!llvm.ident = !{!0}

!0 = metadata !{metadata !"clang version r212716"}

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