[PATCH] D105020: [SLP]Improve graph reordering.

[Alexey Bataev via Phabricator via llvm-commits]

ABataev added a comment.

In D105020#3064191 <https://reviews.llvm.org/D105020#3064191>, @goncharov wrote:

> Hi @ABataev ,
>
> I have found another regression on the latest version of this change:
>
>   > cat repro.cc
>   #include <cstdio>
>   struct a {
>     int b;
>     int c;
>     int o;
>     int d;
>   };
>   class e {
>   public:
>     e(int);
>     void f(a *);
>     int g;
>     int h;
>     int i;
>   };
>   void e::f(a *p) {
>     fprintf(stderr, "MiscompiledFunction\n");
>     fprintf(stderr, "%d, %d, %d, %d, %d, %d\n", p->b, p->c, p->o, p->d, h, g);
>     int j = (p->b + p->c) / 2, k = (p->o + p->d) / 2, l, m;
>     switch (i) {
>     case 0:
>     case 2:
>       l = h - 1 - j;
>       m = g - 1 - k;
>     }
>     p->b = l + p->b - j;
>     p->c = l + p->c - j;
>     p->o = m + p->o - k;
>     p->d = m + p->d - k;
>   }
>   int n = 0;
>   e::e(int q) : g(0), h(0), i(q) {}
>   int main() {
>     a *bb = new a{0, 9, 4, 0}, *p = bb;
>     e r(n);
>     r.f(p);
>     printf("%d %d %d %d\n", bb->b, bb->c, bb->o, bb->d);
>   }
>   > # at 5661317f864abf750cf893c6a4cc7a977be0995a
>   > clang -Wall -Werror -Wextra -O3 -fno-exceptions -stdlib=libc++ -lc++ -std=gnu++17 repro.cc && ./a.out
>   -9 0 -1 -5
>   > # at bc69dd62c04a70d29943c1c06c7effed150b70e1
>   > clang -Wall -Werror -Wextra -O3 -fno-exceptions -stdlib=libc++ -lc++ -std=gnu++17 repro.cc && ./a.out
>   -7 2 -3 -7
>
> It's quite fragile as e.g. removing `fprintf(stderr, "MiscompiledFunction\n");` or running with -fsanitize=null "fixes" the output.

I'll check it, thanks!


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