<html>
<head>
<base href="http://llvm.org/bugs/" />
</head>
<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - dead store elimination nukes live stores due to later memset"
href="http://llvm.org/bugs/show_bug.cgi?id=20303">20303</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>dead store elimination nukes live stores due to later memset
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Scalar Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>nlewycky@google.com
</td>
</tr>
<tr>
<th>CC</th>
<td>hfinkel@anl.gov, llvmbugs@cs.uiuc.edu
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>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"}</pre>
</div>
</p>
<hr>
<span>You are receiving this mail because:</span>
<ul>
<li>You are on the CC list for the bug.</li>
</ul>
</body>
</html>