Re: [PATCH]middle-end fix floating out of constants in conditionals

[Jeff Law <jeffreyalaw@gmail.com>]

On 9/23/22 03:21, Tamar Christina wrote:
> Hi All,
>
> The following testcase:
>
> int zoo1 (int a, int b, int c, int d)
> {
>     return (a > b ? c : d) & 1;
> }
>
> gets de-optimized by the front-end since somewhere around GCC 4.x due to a fix
> that was added to fold_binary_op_with_conditional_arg.
>
> The folding is supposed to succeed only if we have folded at least one of the
> branches, however the check doesn't tests that all of the values are
> non-constant.  So if one of the operators are a constant it accepts the folding.
>
> This ends up folding
>
>     return (a > b ? c : d) & 1;
>
> into
>
>     return (a > b ? c & 1 : d & 1);
>
> and thus performing the AND twice.
>
> change changes it to reject the folding if one of the arguments are a constant
> and if the operations being performed are the same.
>
> Secondly it adds a new match.pd rule to now also fold the opposite direction, so
> it now also folds:
>
>     return (a > b ? c & 1 : d & 1);
>
> into
>
>     return (a > b ? c : d) & 1;
>
> Bootstrapped Regtested on aarch64-none-linux-gnu, x86_64-pc-linux-gnu
> and <on-goin> issues.
>
> Ok for master?
>
> Thanks,
> Tamar
>
> gcc/ChangeLog:
>
> 	* fold-const.cc (fold_binary_op_with_conditional_arg): Add relaxation.
> 	* match.pd: Add ternary constant fold rule.
> 	* tree-cfg.cc (verify_gimple_assign_ternary): RHS1 of a COND_EXPR isn't
> 	a value but an expression itself.
>
> gcc/testsuite/ChangeLog:
>
> 	* gcc.target/aarch64/if-compare_3.c: New test.

OK

jeff