Re: [PATCH] tree-optimization/105679 - disable backward threading of unlikely entry

[Iain Sandoe <idsandoe@googlemail.com>]

Hi Richi,

> On 29 Jul 2022, at 09:54, Richard Biener via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
> 
> The following makes the backward threader reject threads whose entry
> edge is probably never executed according to the profile.  That in
> particular, for the testcase, avoids threading the irq == 1 check
> on the path where irq > 31, thereby avoiding spurious -Warray-bounds
> diagnostics

This breaks bootstrap on i686-darwin{9,17} with what looks like a valid  warning (werrors on stage2)

cc1plus  … -O2 -Wall … is enough to.

I can repeat it on a cross from x86_64-darwin19, so I can probably reduce the .ii (it’s like 2M5 raw) and file a PR if you like - depends if the solution might be obvious to you …

thanks
Iain

--------

In file included from /src-local/gcc-master/gcc/hash-table.h:248,
                 from /src-local/gcc-master/gcc/coretypes.h:486,
                 from /src-local/gcc-master/gcc/tree-ssa-threadbackward.cc:22:
In member function ‘T& vec<T, A, vl_embed>::operator[](unsigned int) [with T = basic_block_def*; A = va_heap]’,
    inlined from ‘const T& vec<T>::operator[](unsigned int) const [with T = basic_block_def*]’ at /src-local/gcc-master/gcc/vec.h:1486:20,
    inlined from ‘bool back_threader_profitability::profitable_path_p(const vec<basic_block_def*>&, tree, edge, bool*)’ at /src-local/gcc-master/gcc/tree-ssa-threadbackward.cc:781:37:
/src-local/gcc-master/gcc/vec.h:890:19: warning: array subscript 4294967294 is above array bounds of ‘basic_block_def* [1]’ [-Warray-bounds]
  890 |   return m_vecdata[ix];
      |          ~~~~~~~~~^
/src-local/gcc-master/gcc/vec.h: In member function ‘bool back_threader_profitability::profitable_path_p(const vec<basic_block_def*>&, tree, edge, bool*)’:
/src-local/gcc-master/gcc/vec.h:635:5: note: while referencing ‘vec<basic_block_def*, va_heap, vl_embed>::m_vecdata’
  635 |   T m_vecdata[1];
      |     ^~~~~~~~~

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