[llvm] [InstCombine] Simplify nonnull pointers (PR #128111)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

> Here's a reduction attempt of the whole preprocessed (might be over-reduced):
> 
> ```
> namespace {
> template <bool, class a> using b = a;
> template <int c> struct ab {
>   static const int aa = c;
> };
> template <class d, class e> struct f : ab<__is_convertible(d, e)> {};
> template <int> struct g {
>   template <class, class h, class... i>
>   using j = g<!h::aa>::template j<h, i...>;
> };
> template <> struct g<false> {
>   template <class k, class> using j = k;
> };
> template <class... l> using m = g<sizeof...(l)>::template j<ab<false>, l...>;
> template <class n, class a> struct ac : m<f<n, a>, int> {};
> template <class a> struct o {
>   typedef a p;
>   p *q;
>   o() : q() {}
>   p *operator->() { return q; }
> };
> template <class a> struct r {
>   a *q;
>   int *s;
>   template <class n, b<ac<n, a>::aa, int> = 0> r(o<n>);
>   o<a> ad() {
>     o<a> t;
>     if (s)
>       t.q = q;
>     return t;
>   }
> };
> } // namespace
> struct ae {
>   int u[];
> };
> struct v {
>   virtual ae y();
> };
> o<v> af;
> struct z : v {
>   z() : w(af) {}
>   ae y() {
>     o x = w.ad();
>     return x->y();
>   }
>   r<v> w;
> };
> void ag() { z(); }
> ```
> 
> cmd: `clang -fno-exceptions -O3 '-std=gnu++20' reduced.ii -emit-llvm -S -o `
> 
> [YutongZhuu](https://github.com/YutongZhuu) can you please take another look?

Can you please provide a single-file, executable reproducer without UB?




https://github.com/llvm/llvm-project/pull/128111