[llvm-dev] Mem2reg: load before single store

[James Y Knight via llvm-dev]

On Mon, Sep 14, 2020 at 3:19 AM László Radnai via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> A problem arises, and I am not sure if it is really a problem or just
> weird C-compliant behavior.
>
> int a; // or, equally, int a=0;
>
> int main(){
>  int b;
>  if (b) // (*)
>

At this line, you invoke undefined behavior by reading the value of "b",
before it's been initialized. At this point, the compiler may do whatever
it likes.
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