[LLVMdev] wrong code generation for memcpy function in SROA optimization pass

[huyanlin19870324]

SROA optimization pass did some optimizations and transforms for memcpy function,such as ld/st operations.When someone has written down code like size>sizeof(dest) in memcpy(*dest,*src,size),
there was much likely a wrong code generation.for example,considered as such testcase:
int main()
{
  char ch;
  short sh = 0x1234;
  memcpy(&ch,&sh,2);
  printf("ch=0x%02x\n",ch);
}
At i586 target,the corect executive result was "ch=0x34",but once openning the SROA optimization
pass it turned out as "ch=0x00".
    Then I had a try to dump IR code for comparsion between before and after SROA optimization pass.
IR before SROA:
define i32 @main() #0 {
entry:
  %retval = alloca i32,align 4,
  %ch = alloca i8,align 1,
  %sh = alloca i16,align 2,
  store i32 0,i32* %retval,
  store i16 4660,i16* %sh,align 2,!tbaa!0,
  %0 = bitcast i16* %sh to i8*
  call void @llvm.memcpy.p0i8.p0i8.i32(i8* %ch,i8* %0,,i32 2,i32 1,i1 false),
  %1 = load i8* ch,align 1,!tbaa!0,
  %conv = sext i8 %1 to i32,
  %call = call i32 (i8*,...)* @printf(i8* getelementptr inbounds([9*i8]*@.str,i32 0,i32 0),i32 %conv),
  ret i32 0,
}
IR after SROA:
define i32 @main() #0 {
entry:
  %conv = sext i8 undef to i32,
  %call = call i32 (i8*,...)* @printf(i8* getelementptr inbounds([9*i8]*@.str,i32 0,i32 0),i32 %conv),
  ret i32 0,
}
    Then I tried to debbuging with SROA.cpp,I found in funcction visitMemTransferInst,it accorded the IR instruction "call void @llvm.memcpy.p0i8.p0i8.i32(i8* %ch,i8* %0,,i32 2,i32 1,i1 false)",would produce such codes(finally,memcpy disappeared and the codes would be delated,IR after SROA become incorrect ,am i right?)
%sh.0.cast = bitcast i8* ch to i16*,
%sh.0.copyload = load i16* sh,align 1,
store i16 %sh.0.copyload,i16* %sh.0.cast,align 1,
 
     In a word,I think visitMemTransferInst function in SROA.cpp had maken a incorrect optimization for memcpy in the situation like memcpy's size>sizeof(dest).
am i write? I would appreciate any suggestions on this.Thanks very much!
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20131124/547a6d6c/attachment.html>