Re: [GCC 9 backport] cplxlower: Avoid a transform when looking at a default definition

[Richard Biener <richard.guenther@gmail.com>]

On Wed, Mar 30, 2022 at 11:52 AM Martin Jambor <mjambor@suse.cz> wrote:
>
> Hi,
>
> I did not backport my fix of PR 97456 to GCC 9 and it re-surfaced there
> as PR 105071.  I have cherry-picked the fix, pasted below, on top of the
> gcc 9 branch (the only change is an extra bug reference in the
> ChangeLog) and made sure it passes bootstrap and testing on
> x86_64-linux.  Can I commit the backport to the branch?

OK

> I think the old testcase is sufficient and so did not add the new one.
>
> Thanks,
>
> Martin
>
>
>
>
> In PR 97456, IPA-SRA triggers a bug in tree-complex.c where it
> converts:
>
>  <bb 2>
>    a$_M_value_21 = COMPLEX_EXPR <ISRA.18_10(D), ISRA.18_10(D)>;
>
> (where ISRA.18 is IPA-SRA created PARM_DECL with DECL_IGNORED_P set,
> which is why it only happens with IPA-SRA) into:
>
>   <bb 2>
>     a$_M_value_21 = COMPLEX_EXPR <a$_M_value$real_10(D), a$_M_value$real_10(D)>;
>
> i.e. it replaces two uses of the parameter default-def with two
> uninitialized default-defs of a new variable - all in hope to produce
> code with better debug info.
>
> This patch fixes it by avoiding the transform when the SSA_NAME to be
> replaced is a default definition.
>
> gcc/ChangeLog:
>
> 2020-10-19  Martin Jambor  <mjambor@suse.cz>
>
>         PR tree-optimization/97456
>         PR middle-end/105071
>         * tree-complex.c (set_component_ssa_name): Do not replace ignored decl
>         default definitions with new component vars.  Reorder if conditions.
>
> gcc/testsuite/ChangeLog:
>
> 2020-10-19  Martin Jambor  <mjambor@suse.cz>
>
>         PR tree-optimization/97456
>         * gcc.dg/tree-ssa/pr97456.c: New test.
>
> (cherry picked from commit 619f91eaa8c8a50f1f9d3e7b96ee837037f0e806)
> ---
>  gcc/testsuite/gcc.dg/tree-ssa/pr97456.c | 40 +++++++++++++++++++++++++
>  gcc/tree-complex.c                      |  3 +-
>  2 files changed, 42 insertions(+), 1 deletion(-)
>  create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr97456.c
>
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr97456.c b/gcc/testsuite/gcc.dg/tree-ssa/pr97456.c
> new file mode 100644
> index 00000000000..5171c9b4577
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr97456.c
> @@ -0,0 +1,40 @@
> +/* { dg-do run } */
> +/* { dg-options "-O2 -fwhole-program" } */
> +
> +
> +float val2 = 1.710780f;
> +float val3;
> +volatile float vf;
> +
> +int __attribute__((noipa))
> +get_bool (void)
> +{
> +  return 1;
> +}
> +
> +int __attribute__((noinline))
> +wrong (float *pos)
> +{
> +  _Complex float a;
> +
> +  __real__ a = *pos;
> +  __imag__ a = *pos;
> +
> +  _Complex float b = 0 + 0i;
> +
> +  b = b + a;
> +
> +  if (b == 0.0f)
> +    return 1;
> +
> +  vf = __imag__ b;
> +  return 0;
> +}
> +
> +int main(int argc, char **argv) {
> +  float val = get_bool () == 1 ? val2 : val3;
> +
> +  if ((wrong(&val), wrong(&val)))
> +    __builtin_abort ();
> +  return 0;
> +}
> diff --git a/gcc/tree-complex.c b/gcc/tree-complex.c
> index d4b053d68e1..36a4d6f06d5 100644
> --- a/gcc/tree-complex.c
> +++ b/gcc/tree-complex.c
> @@ -569,7 +569,8 @@ set_component_ssa_name (tree ssa_name, bool imag_p, tree value)
>      {
>        /* Replace an anonymous base value with the variable from cvc_lookup.
>          This should result in better debug info.  */
> -      if (SSA_NAME_VAR (ssa_name)
> +      if (!SSA_NAME_IS_DEFAULT_DEF (value)
> +         && SSA_NAME_VAR (ssa_name)
>           && (!SSA_NAME_VAR (value) || DECL_IGNORED_P (SSA_NAME_VAR (value)))
>           && !DECL_IGNORED_P (SSA_NAME_VAR (ssa_name)))
>         {
> --
> 2.35.1
>