[LLVMdev] Is it an opt bug ?

[Seb]

Hi all,

I'm looking at following code snippet:

void t2(double *x)
{
      long long a[2];
      a[0] = 3;
      a[1] = 5;
      *x = * ((double *) a);
      *(x+1) = * ((double *) &a[a[0]-2]);
}

I use generate LLVM code using my own front-end that looks like:


; ModuleID = 'jb.c'
target datalayout =
"e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:32:32-n8:16:32"
target triple = "i386-pc-linux-gnu"
define void @t2(double* %x) {
L.entry:
    %a = alloca [2 x i64], align 4

    %x.addr = alloca double*
    store double* %x, double** %x.addr
    %0 = bitcast [2 x i64]* %a to i64*
    store i64 3, i64* %0
    %1 = getelementptr [2 x i64]* %a, i32 0, i32 1
    store i64 5, i64* %1
    %2 = bitcast [2 x i64]* %a to double*
    %3 = load double* %2
    %4 = load double** %x.addr
    store double %3, double* %4
    %5 = bitcast [2 x i64]* %a to double*
    %6 = bitcast double* %5 to i8*
    %7 = bitcast [2 x i64]* %a to i64*
    %8 = load i64* %7
    %9 = sub i64 %8, 2
    %10 = trunc i64 %9 to i32
    %11 = mul i32 %10, 8
    %12 = getelementptr i8* %6, i32 %11
    %13 = bitcast i8* %12 to double*
    %14 = load double* %13
    %15 = load double** %x.addr
    %16 = bitcast double* %15 to i8*
    %17 = getelementptr i8* %16, i32 8
    %18 = bitcast i8* %17 to double*
    store double %14, double* %18
    ret void
}

when I use LLVM opt on this .ll file I've got:

; ModuleID = 'jb.ll'
target datalayout =
"e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:32:32-n8:16:32"
target triple = "i386-pc-linux-gnu"

define void @t2(double* nocapture %x) nounwind {
L.entry:
  store double 1.482197e-323, double* %x, align 4
  ret void
}

Now if I use clang -O2 I've got following llvm file:

; ModuleID = 'jb.clang.ll'
target datalayout =
"e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:32:32-n8:16:32"
target triple = "i386-unknown-linux-gnu"

define void @t2(double* nocapture %x) nounwind {
  store double 1.482197e-323, double* %x, align 4, !tbaa !0
  %1 = getelementptr inbounds double* %x, i32 1
  store double 2.470328e-323, double* %1, align 4, !tbaa !0
  ret void
}

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

Which is what I was expecting, to me it seems that there is a bug in LLVM
opt, is it the case ?

Thanks for your answer
Best Regards
Seb
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20120228/f4e73059/attachment.html>