[Bug tree-optimization/92980] [miss optimization]redundant load missed by fre.

[crazylht at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92980

--- Comment #3 from Hongtao.liu <crazylht at gmail dot com> ---
(In reply to Andrew Pinski from comment #2)
> I think the problem is we are folding the right side of the array (with the
> conversion to size_t) too early.
> That is:
> src1[j-1]
> 
> Is being folded too early to have (j-1)*4
> 
> Fixing this up in match.pd is wrong.
> 
> This gets us the best code without any patch to match.pd:
> int foo(unsigned int *__restrict src1, int i, int k, int n)
> {
>   int j = k + n;
>   int sum = src1[j];
>   int jj = j-1;
>   sum += src1[jj];
>   if (i <= k)
>     {
>       j+=2;
>         int ii = j-3;
>       sum += src1[ii];
>     }
>   return sum + j;
> }
> 
> See how j-1 and j-3 are not folded early and that fixes the issue.

It's done by parser, cut from c-common.c
----------
3182       if (TREE_CODE (intop) == MINUS_EXPR)
3183         subcode = (subcode == PLUS_EXPR ? MINUS_EXPR : PLUS_EXPR);
3184       /* Convert both subexpression types to the type of intop,
3185          because weird cases involving pointer arithmetic
3186          can result in a sum or difference with different type args.  */
3187       ptrop = build_binary_op (EXPR_LOCATION (TREE_OPERAND (intop, 1)),
3188                                subcode, ptrop,
3189                                convert (int_type, TREE_OPERAND (intop,
1)),
3190                                true);
3191       intop = convert (int_type, TREE_OPERAND (intop, 0));
3192     }

----------

ptrop ---> src1 + 18446744073709551612;
intop ---> j

It seems on purpose???