[lldb-dev] Is bitcast breaking lldb a bug?

Levo DeLellis via lldb-dev lldb-dev at lists.llvm.org
Wed Feb 26 03:31:04 PST 2020

This feels like a bug to me. Yesterday I was asking what the rules were
because it felt like things change and break randomly. Now I have a good
example. (link to my email yesterday

Take this example source file

int main() {
    int dummy = 25;
    short wtf[dummy];
    memset(wtf, 0, dummy*sizeof(*wtf));
    return 0;

Now emit the llvm-ir so we can edit it

clang -g test.c -S -emit-llvm

Before line 21 write this line

%z8 = bitcast i16* %8 to i16*

Change the `metadata i16* %8` to `metadata i16* %z8`. Compile it then debug
line 4 `clang -g wtf.ll` `lldb-9 ./a.out` `break set -f test.c -l 4` `r`
`frame variable`

You'll see the array doesn't show up. If you change %z8 back to %8 it will
reappear. Is this a bug or can I not use bitcast when I'm trying to do
things with llvm.dbg.declare/addr/value?
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