[LLVMbugs] [Bug 13734] New: Inefficient code for passing a non-pod by value

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=13734

             Bug #: 13734
           Summary: Inefficient code for passing a non-pod by value
           Product: clang
           Version: unspecified
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: C++
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: rafael.espindola at gmail.com
                CC: dgregor at apple.com, llvmbugs at cs.uiuc.edu
    Classification: Unclassified


Given

struct ostreambuf_iterator {
  int* _M_sbuf;
  bool _M_failed;
  ostreambuf_iterator();
};
void do_put(ostreambuf_iterator) ;
struct num_put {
  void put(ostreambuf_iterator __s) const ;
};
void num_put::put(ostreambuf_iterator __s) const{
  do_put(__s);
}

clang now produces

define void @_ZNK7num_put3putE19ostreambuf_iterator(%struct.num_put* nocapture
%this, i32* %__s.coerce0, i8 %__s.coerce1) uwtable optsize ssp align 2 {
  %__s = alloca %struct.ostreambuf_iterator, align 8
  %1 = alloca %struct.ostreambuf_iterator, align 8
  %2 = getelementptr inbounds %struct.ostreambuf_iterator* %__s, i64 0, i32 0
  store i32* %__s.coerce0, i32** %2, align 8
  %3 = getelementptr %struct.ostreambuf_iterator* %__s, i64 0, i32 1
  store i8 %__s.coerce1, i8* %3, align 8
  %4 = bitcast %struct.ostreambuf_iterator* %1 to i8*
  %5 = bitcast %struct.ostreambuf_iterator* %__s to i8*
  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %4, i8* %5, i64 9, i32 8, i1 false)
  %6 = getelementptr inbounds %struct.ostreambuf_iterator* %1, i64 0, i32 0
  %7 = load i32** %6, align 8
  %8 = getelementptr %struct.ostreambuf_iterator* %1, i64 0, i32 1
  %9 = load i8* %8, align 8
  call void @_Z6do_put19ostreambuf_iterator(i32* %7, i8 %9) optsize
  ret void
}

Before r162254 we used to produce


define void @_ZNK7num_put3putE19ostreambuf_iterator(%struct.num_put* nocapture
%this, i32* %__s.coerce0, i8 %__s.coerce1) uwtable optsize ssp align 2 {
  tail call void @_Z6do_put19ostreambuf_iterator(i32* %__s.coerce0, i8
%__s.coerce1) optsize
  ret void
}

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